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Eco-physiological changes in sorghum hybrids released in Argentina over the last 30 years
Abstract
The development of single-cross hybrids during mid-1950s was important for sorghum [Sorghum bicolor (L.) Moench] improvement worldwide. Within the hybrid era, however, there is limited information on sorghum genetic progress. Our main objective was to evaluate the genetic gain for grain yield and other phenotypic traits for grain sorghum commercial hybrids released in Argentina from 1984 to 2014. A second objective was to describe common attributes behind high-yielding hybrids. A total of 43 hybrids were grown at three different environments. Evaluated traits were grain yield, yield components (grain number m⁻² and individual grain weight), phenology, plant height, stay-green, crop growth rate around flowering, reproductive biomass partitioning, grain set efficiency, biomass at maturity, harvest index and post-anthesis source/sink ratio.
Yield across environments varied from 8.1 to 10.8 t ha⁻¹. Genetic progress for grain yield was 8.7 ± 2.9 kg ha⁻¹ year⁻¹ (p < 0.01) across environments. This progress represented only 0.1% of the experiments mean grain yield. Modern hybrids set more grains per unit of reproductive biomass (p < 0.10), have more stay-green (p < 0.10), and showed higher post-anthesis source/sink ratio (p < 0.10) when compared to older ones. By clustering hybrids irrespective of the year of market release, three groups were conformed showing important grain yield differences. Common traits among high-yielding hybrids were high grain number, low grain size, later flowering time, intermediate height and stay-green trait. Within the high-yielding cluster, hybrids showed significant variability in crop growth rate around flowering, biomass at maturity, reproductive biomass partitioning, grain set efficiency, harvest index and post-anthesis source/sink ratio that could be exploited in breeding programs, describing opportunities for sorghum improvement in temperate environments.
... Several studies on the genetic gain in sorghum have been reported across the world in the regions of United States (Smith and Frederiksen, 2000;Pfeiffer et al., 2018), Australia (Stephens et al., 2012), Argentina (Gizzi and Gambin, 2016), Mali (Rattunde et al., 2016), Ethiopia (Chala et al., 2019), Haiti (Muleta et al., 2019). However, compared to other crops, there are far fewer studies examining the changes occurring due to long-term selection within sorghum breeding programs in India. ...
... In absolute terms, we have found that the genetic gain in grain sorghum (44.93 kgha -1 yr -1 ) is similar to soybean (43 kg/ha/yr) (De Felipe et al., 2016) but it was lower than in maize (55-75 kg/ha/yr) (Apraku et al., 2022). In sorghum, we have reported much higher genetic gains for grain in varieties compared to that of 8.7 kg/ha/yr in hybrids of Argentina (Gizzi and Gambin, 2016) and 8 kg/ha/yr in both hybrids and inbred lines of USA (Pfeiffer et al., 2018). The low genetic gain in the former attributed to irregular breeding efforts for quality improvement (tannin concentration and fat content) could mean that the continuous sorghum breeding efforts in India were successful as evident by high genetic gains and also that breeding for stress-tolerance (grain mold and shoot fly tolerance)was more fruitful compared that of quality improvement (Gizzi and Gambin, 2016). ...
... In sorghum, we have reported much higher genetic gains for grain in varieties compared to that of 8.7 kg/ha/yr in hybrids of Argentina (Gizzi and Gambin, 2016) and 8 kg/ha/yr in both hybrids and inbred lines of USA (Pfeiffer et al., 2018). The low genetic gain in the former attributed to irregular breeding efforts for quality improvement (tannin concentration and fat content) could mean that the continuous sorghum breeding efforts in India were successful as evident by high genetic gains and also that breeding for stress-tolerance (grain mold and shoot fly tolerance)was more fruitful compared that of quality improvement (Gizzi and Gambin, 2016). The low genetic progress rates estimated by Pfeiffer et al. (2018) attributed to limited genetic diversity within their crop breeding program implied the high genetic diversity within the Indian sorghum breeding program.The 24 sorghum varieties were developed through pedigree method of selection involving hybridization between landraces and elite breeding lines, resistant germplasm lines and improved varieties. ...
Sorghum is a climate-resilient cereal and staple food crop for more than 200 million people in arid and semi-arid countries of Asia and Africa. Despite the economic importance, the productivity of sorghum in India is constrained by biotic and abiotic stresses such as incidences of shoot fly, grain mold and drought. Indian sorghum breeding focused on dual-purpose (grain and fodder), short-duration varieties with multiple resistance/tolerance to pests and diseases and improved nutritional quality (high protein, iron and zinc and low fat). In this context, it is important to ascertain the genetic progress made over 30 years by assessing the efficiency of past achievements in genetic yield potential and to facilitate future genetic improvement. The current study determined the genetic gain in 24 sorghum varieties developed by the national and state level research systems during 1990-2020. The 24 varieties were evaluated for three years (2018-2020) at six locations in Telangana state for yield, nutritional characteristics and tolerance to shoot fly and grain mold. The absolute grain yield genetic gain from the base year 1990 is 44.93 kg/ha/yr over the first released variety CSV 15. The realized mean yield increased from 2658 kg/ha of the variety CSV 15 in 1990s to 4069 kg/ha of SPV 2579 developed in 2020s. The absolute genetic gain for grain mold resistance is -0.11 per year with an overall relative gain of 1.46% over CSV 15. The top varieties for grain yield (SPV 2579, SPV 2678 and SPV 2578), fodder yield (PYPS 2, SPV 2769 and SPV 2679), shoot fly tolerance (PYPS 8, PYPS 2 and SPV 2179), mold tolerance (PYPS 8, PYPS 2 and SPV 2579) and high protein (PYPS 8, PYPS 2 and SPV 2769) were identified for possible scale up and further use in breeding program diversification. The study revealed that sorghum varieties bred with diverse genetic backgrounds such as landraces and with tolerance to pests and diseases had stable yield performance. Application of genomics and other precision tools can double genetic gains for these traits to strengthen sorghum cultivation in rainfed areas serving food and nutrition security.
... Recent studies revealed that grain yield has increased from 1960 to 2010s in commercial sorghum hybrids and in inbreed lines (Pfeiffer et al., 2019). Furthermore, understanding the physiological determinants of yield stability can improve decision making at advanced stages of selection (Gizzi & Gambin, 2016;Messina et al., 2020). ...
... Globally, yield gains reported for sorghum range from 8 to 44 kg ha −1 yr −1 (0.2-0.7% yr −1 ) (Gizzi & Gambin, 2016;Mason et al., 2008;Pfeiffer et al., 2019) for similar historical periods to this study. Here we show that genetic improvement in elite U.S. sorghum hybrids has been mainly associated with improvements in the reproductive efficiency (grain number per unit biomass) and harvest index of the crop. ...
... Experimental results supports the hypothesis that sorghum yield gain was mainly supported by changes in grain number per unit area (96 grains m −2 yr −1 ), similar to those reported for U.S. commercial (Mason et al., 2008) and public hybrids (Pfeiffer et al., 2019). Gizzi and Gambin (2016) observed DEMARCO ET AL. ...
Understanding physiological changes in response to long‐term selection for yield can inform breeding decisions and hasten genetic gain. The objective of this study was to characterize changes over time in yield‐relevant physiological traits for hybrids with different years of release for grain sorghum ( Sorghum bicolor L. Moench). Field trials were conducted during the 2018 and 2019 seasons in 8 site‐years across the states of Kansas and Texas including 20 commercially available grain sorghum hybrids released by Pioneer between 1963 and 2017. Detailed yield‐related physiological traits were determined in 2 site‐years including grain yield and its components, grain filling, plant biomass, panicle length, and water‐soluble carbohydrates (WSC) during the reproductive period. Consistent with estimates using historical yield data, sorghum yield improvement was 27 kg ha ⁻¹ yr ⁻¹ . For the 2 site‐years with detailed yield‐related physiological traits, no changes in final grain weight, grain‐filling duration, and rate over time were documented. In contrast, grain number increased at a rate of 100 grains m ⁻² yr ⁻¹ . Modern hybrids had larger panicle size and showed greater accumulation of WSC during vegetative period (as measured at the start of flowering) and greater remobilization of WSC during the reproductive period (after flowering) to grain, thus, maintaining grain size on the increased grain number per unit area and harvest index. These findings suggest that WSC dynamics play a critical role on past genetic yield gain in sorghum and its potential for future improvements should be considered.
... Maize yield gains under stress were associated with increased kernel number per unit of land area through increased kernel number per ear, and reduced anthesis-silking interval and barrenness (Campos et al., 2006). By contrast, sorghum genetic yield gain has been limited by several causes, as continuous shifting production environments due to competition with other crops, changes in priority traits targeted to breeding, less-than-optimized heterotic groups, and lower research investments due to discontinued or reduced breeding programs (Gizzi and Gambin, 2016;Pfeiffer et al., 2019). Reported genetic yield gain ranged from 0.5 to 1.5% year − 1 for maize and only 0.08 to 0.41% year − 1 for sorghum (Mason et al., 2008;Fischer et al., 2014;Gizzi and Gambin, 2016;Pfeiffer et al., 2019;Mayor et al., 2020). ...
... By contrast, sorghum genetic yield gain has been limited by several causes, as continuous shifting production environments due to competition with other crops, changes in priority traits targeted to breeding, less-than-optimized heterotic groups, and lower research investments due to discontinued or reduced breeding programs (Gizzi and Gambin, 2016;Pfeiffer et al., 2019). Reported genetic yield gain ranged from 0.5 to 1.5% year − 1 for maize and only 0.08 to 0.41% year − 1 for sorghum (Mason et al., 2008;Fischer et al., 2014;Gizzi and Gambin, 2016;Pfeiffer et al., 2019;Mayor et al., 2020). ...
... The grain yield superiority of maize over sorghum was also observed when crops were compared at their specific optimum sowing dates (November for sorghum vs. October and December for maize). These results support the concept that the higher genetic gains for yield potential and stress tolerance of maize relative to sorghum (Tollenaar and Lee, 2002;Campos et al., 2004;Gizzi and Gambin, 2016;Borrás and Vitantonio-Mazini, 2018) is the main driver behind current crop yield differences, based on more and heavier grains (Mason et al., 2008). Results are also consistent with the contrasting pattern of historic yield and recent dominance of maize over sorghum across the different regions of Argentina (Parra et al., 2020). ...
Yield genetic gains have been significantly higher for maize (Zea mays L.) than for sorghum (Sorghum bicolor L. Moench). Today there is questioning under which environments sorghum is a better option than maize, since maize has increased its tolerance to water and N limitations. For this we conducted eleven rainfed experiments at different sites around the central region of Argentina, using representative commercial genotypes of each crop. Experiments involved different sowing dates and N fertilization treatments, generating a total of 21 growing conditions where both crops were simultaneously compared. Measured traits included yield, phenology, leaf area development, light interception, and biomass accumulation. Explored growing conditions yielded from 1.8 to 11.7 Mg ha-1 for maize, and from 1.4 to 9.9 Mg ha-1 for sorghum. Crops yield difference (maize minus sorghum) ranged from -0.3 to 4.8 Mg ha-1, and this difference significantly favoured maize in all growing conditions except one. As expected, the yield difference in favor to maize increased in magnitude in the environments with more positive water balance (r: 0.54; p<0.01) and higher N levels (r: 0.43; p<0.05). When compared to maize, sorghum always showed a longer time to anthesis and a shorter grain-filling duration, higher LAI, lower post-anthesis biomass accumulation, and similar total biomass at physiological maturity. Maize harvest index was higher and less variable than the sorghum one (0.44 to 0.56 and 0.28 to 0.45, for maize and sorghum, respectively). A comparison with previous literature showed that the cut-off yield (i.e., maize yield below which sorghum has better yield performance) is significantly lower than expected. Results reinforce previous evidence highlighting that the differential research investment in the two crops is limiting the capacity of sorghum to out-yield maize across environments.
... A recent study in the US indicated a sorghum genetic yield gain of 8 kg ha −1 year −1 , or 0.08 % year −1 of the most recent genotype yield, from 1960 to 2010 (Pfeiffer et al., 2019). In Argentina, sorghum genetic yield gain was 8.7 kg ha −1 year −1 , or 0.09 % year −1 , for the period 1984−2014 (Gizzi and Gambin, 2016). Factors behind these low rates are similar in both countries, including continuous shifting production environments due to competition with other crops (i.e., sorghum has been displaced to more marginal areas), changes in priority traits targeted by breeding, less-than-optimized heterotic groups, and lower research investments due to discontinued or reduced breeding programs, when compared with other crops (Gizzi and Gambin, 2016;Pfeiffer et al., 2019). ...
... In Argentina, sorghum genetic yield gain was 8.7 kg ha −1 year −1 , or 0.09 % year −1 , for the period 1984−2014 (Gizzi and Gambin, 2016). Factors behind these low rates are similar in both countries, including continuous shifting production environments due to competition with other crops (i.e., sorghum has been displaced to more marginal areas), changes in priority traits targeted by breeding, less-than-optimized heterotic groups, and lower research investments due to discontinued or reduced breeding programs, when compared with other crops (Gizzi and Gambin, 2016;Pfeiffer et al., 2019). ...
... Interestingly, sorghum stability has also improved slightly. Breeding is probably responsible for this, via increased staygreen and post-anthesis source-sink ratio (Gizzi and Gambin, 2016). Extended foliar greenness was associated with higher yield under water limited conditions (Rosenow et al., 1983;Borrell et al., 2000). ...
Sorghum (Sorghum bicolor L. Moench) is traditionally known for its better adaptation to drought when compared to other cereals like maize (Zea mays L.). However, genetic gains are significantly higher for maize than for sorghum, and are known to include drought tolerance. We analyzed maize and sorghum harvested area, yield, and yield stability using publically available farm data from 1970 to 2016 in Argentina, where both crops are sown across a large environmental gradient (water balance from ca.−400 to −1100 mm year⁻¹). Yield stability was assessed by analyzing county yield residuals relative to average yields.
Both crops had comparable yields in 1970, but showed a different yield progress (ca. 110 kg ha⁻¹ year⁻¹ or 1.73 % year⁻¹ and 62 kg ha⁻¹ year⁻¹ or 1.26 % year⁻¹ for maize and sorghum, respectively). Yield difference in favor to maize became more evident since late 90´s, together with the introduction of genetically modified (GM) materials in this crop. Today this consistent maize yield advantage over sorghum is observed across all regions, even those with more frequent water shortages. It also impacted in the maize area, being 6-fold larger than that of sorghum in 2016. Sorghum yield stability was traditionally higher than that of maize (maize yield relative residuals were 4–15 % higher than that of sorghum), but today both crops have similar yield stability in most regions. Yield progress showed comparable rates to reported genetic gains for maize (0.85–1.74 % year⁻¹), but not for sorghum (0.09 % year⁻¹). The contrasting investment in breeding, GM traits, and agronomy explains major differences between crops, and can be extrapolated to other countries where both crops have differential genetic yield gains. Sorghum yield stability is desirable in marginal areas, but alternative benefits (higher residue, non-GM gluten free grain for specialty markets) might be more important in the future for promoting this crop.
... Next, we used random-effects models and ordinary least squares regressions to calculate the genetic gain of the HI in line with previous era studies (de la Vega et al., 2007;Haegele et al., 2013;Gizzi and Gambin, 2016;de Felipe et al., 2016). This approach provides a proper estimate of the genotype regardless of the effect of the growing conditions and unbalanced datasets (Smith et al., 2005;de la Vega et al., 2007;Gizzi and Gambin, 2016). ...
... Next, we used random-effects models and ordinary least squares regressions to calculate the genetic gain of the HI in line with previous era studies (de la Vega et al., 2007;Haegele et al., 2013;Gizzi and Gambin, 2016;de Felipe et al., 2016). This approach provides a proper estimate of the genotype regardless of the effect of the growing conditions and unbalanced datasets (Smith et al., 2005;de la Vega et al., 2007;Gizzi and Gambin, 2016). First, the best linear unbiased predictors (BLUPs) for the HI of each hybrid were obtained from linear random-effects models using the function lmer in the lme4 R package (Bates et al., 2015;R Core Team, 2021). ...
Context: Quantifying historical changes in maize harvest index (HI), the fraction of above-ground biomass allocated to grain yield, can enhance our ability to explain grain yield trends and estimate stover carbon inputs for sustainability assessments. However, the HI genetic gain has not been the primary focus of previous era
studies.
Objective: The aim of this study is to enhance our knowledge of maize HI genetic gain. Our first objective is to quantify HI genetic gain in Bayer Crop Science Legacy hybrids and investigate the contribution of breeding and agronomic management. Our second objective is to develop a general-use model to describe the temporal evolution of maize HI.
Methods: We studied 54 commercial hybrids (103-day and 111-day relative maturities) released from 1983 to
2020 across 13 environments, including plant density (current and historical increasing rate) and N-fertilizer (low and sufficient N rates) treatments. The HI was estimated at physiological maturity by destructively sampling plants. Then we synthesize new experimental data with literature findings (n = 16) to provide a robust HI genetic gain estimate.
Results: Results showed that HI has increased over the years from 0.516 to 0.571 in 103-day hybrids and from 0.537 to 0.584 in 111-day hybrids. The genetic gains were similar across environments and management treatments within the studied range, indicating that this increase is attributed to maize breeding. The N-fertilizer
treatments affected the magnitude of the HI, but plant density did not. Our results, combined with 16 literature datasets, revealed a 0.26% year-1 relative increase in HI since 1964. We estimated that the increase in HI accounts for ca. 15% of the historical maize yield increase in the US Corn Belt over the past 50 years.
Conclusions: The maize HI has increased over the last 50 years, and this increase was attributed to breeding, not to management.
Significance: Our findings enhance our knowledge of maize HI, will support robust estimations of carbon inputs in sustainability studies, and inform crop models to better capture historical yield increases.
... In spite of the fact that traditional varieties are still cultivated, here and there, on large scale, this strategy resulted, in recent years, in an increased number of newly released varieties proposed to replace old ones (Benbelkacem, 2014;Rabti et al., University of Algeria, personal communication). Several studies, conducted mainly under favorable environments, reported that replacement of traditional cultivars was accompanied by positive changes in grain yield, yield components, harvest index, earliness and plant height reduction (Battenfield et al., 2013;Fischer et al., 2014;Sanchez-Garcia et al., 2013;Gizzi and Gambin, 2016;Laidig et al., 2017;Wang et al., 2017;Rabti et al., University Algeria, personal communication). In this context, Joudi et al. (2014) reported a rate of grain yield increase varying from 20 and 30 kg/ha/year, under respectively rainfed and irrigation conditions. ...
... Performances comparison of traditional and recently released varieties indicated that post-green revolution varieties exhibited significant increase in grain yield and grain yield components and harvest index and significant decrease in plant height, straw yield and lateness; with no significant changes in biomass, spike fertility and kernel weight, on average. These results corroborated findings of several researches (Alvaro et al., 2008;Battenfield et al., 2013;Fischer et al., 2014;Sanchez-Garcia et al., 2013;Gizzi and Gambin, 2016;Laidig et al., 2017;Wang et al., 2017;Rabti et al., University of Algeria, personal communication). Rate of grain yield increase was estimated to be equal to 11.56 kg/ha/year, which is well below figures reported from favorable environments (Zhou et al., 2007 ;Cargnin et al., 2009;Joudi et al., (2014), but closer to those reported from similar water -limited environments Battenfield et al., 2013;Keser et al., 2017). ...
A field experiment was conducted during the 2017/18 cropping season at the Field Crop Agricultural Experimental Station Institute of Setif, Algeria. The study aimed to investigate the performance and variability of agro-morphological traits present in a set of local durum wheat varieties, registered during the 1950–2017 period and to estimate grain increase and to identify concurrent trait changes accompanying yield increase. The results indicated ample variation for the measured traits. Multivariate analysis grouped the assessed varieties into: high vs low grain yield, tall, late vs early and dwarf and high
fertility, low kernel weight vs low fertility, high kernel weight varieties. Post-green revolution varieties performed significantly more than traditional varieties in terms of grain yield, yield components and harvest index. Local varieties were taller, late to head and had high straw yield. Grain yield genetic progress over time was estimated to be equal to 11.56kg/ha/year. Differences between local and recently released varieties are ascribed to Rht genes. To make the best use of desirable characteristics from local and modern varieties, it is suggested to further investigate the variation of dwarfing genes
in the tested plant material. This allows to design a breeding program promoting the development of new germplasm more adapted to rain-fed south Mediterranean environments, through selection for dwarfing genes, like Rht24 and Rht8, which express minor effects on the desirable traits in low yield environment.
... The genetic gain measured in this study is higher than that reported in prior comparative studies for the U.S. (Mason et al., 2008;Pfeiffer et al., 2019) and Argentina (Gizzi & Gambin, 2016). This discrepancy may be due to a number of factors including germplasm, sample size, but also the discrepancy in the level of investment between public and private breeding programs. ...
Sorghum [Sorghum bicolor (L.) Moench] is an important staple food for human consumption and a source of animal feed in the semiarid regions of the world. Sustained positive rates of crop improvement are necessary to supply food and feed to a growing population. However, land allocated to sorghum and its inclusion in production systems has been in constant decline. Here we report the rate of sorghum genetic gain in a commercial breeding program in the US and provide evidence that a modest yield improvement is an important factor limiting land allocation to this crop. A six‐year study that evaluated fifty sorghum genotypes commercialized between the decades of 1960 and 2010 was conducted in nineteen environments within the US Sorghum belt region. Yield varied between 500 and 850 g m−2. Here we show a positive rate of genetic gain of 2.63 g m−2 y−1 on average across three different maturity groups grown in the US. Rates ranged from 2.1 to 4.3 g m−2 y−1 across maturity groups. This result contrasts with a stagnant rate of crop improvement for many regions of the world, yet the rates are insufficient to reverse the negative trend in planted area. Breeding technologies are proposed to hasten genetic gain in sorghum to reverse the loss of on‐farm agricultural biodiversity. This article is protected by copyright. All rights reserved
... However, the crop with the highest negative balance per hectare was sorghum. Because sorghum is a crop that adapts well to low-fertility, saline and floodable soils (Gizzi and Gambin, 2016), it was used mainly in the low-yielding lands of the country. In these areas, fertilization is usually low or even cero, so sorghum takes the N available from the soil. ...
Argentina has a long tradition of agricultural systems that use few amounts of fertilizers. However, the crop nutrient balance remains unknown throughout the country. In this study, we estimated the nitrogen (N), phosphorus (P) and sulfur (S) balance at national and subnational scale of the six major grain crops: soybean, maize, wheat, sunflower, barley and sorghum. We found a negative spatio-temporal NPS balance with an annual average deficit of −22.4 kg ha⁻¹ year⁻¹ for N, −6.9 kg ha⁻¹ year⁻¹ for P and −2.1 kg ha⁻¹ year⁻¹ for S. Considering the whole agricultural area analyzed, the balance represented a mean annual negative net outflow of 612 thousand tons (kT) of N, 166 kT of P and 58 kT of S. The nutrient balance was not homogeneous across the country, with significant differences among the three major productive regions: i) the Pampean nucleus region (−32.2, −8.5, −2.92 kg ha⁻¹ year⁻¹, for N, P and S respectively) ii) the non-nucleus Pampean region (−14.3, −3.7, −2.03 kg ha⁻¹ year⁻¹ for N, P and S respectively), and iii) extra-Pampean region (−22.4, −6.3, −2.13 kg ha⁻¹ year⁻¹ for N, P and S respectively). Remarkably, despite having the highest N and P application rate, the Pampean nucleus region has the largest deficit of the analyzed nutrients. Soybean was the main driver of the nutrient mining in the country, accounting for 62 % of the NPS deficits at national scale (−418 kT N year⁻¹, −120 kT P year⁻¹ and −35 kT S year⁻¹). Our findings suggest that the current fertilization practices applied to the major extensive crops in Argentina are far from being sufficient to supply the nutrients they demand, even cultivating soybean that is a N-fixing crop. These results highlight that Argentine main crops' high productivity is reached at the expense of soil nutrient depletion.
... Sorghum hybrids in the United States have increased yield over the past decades by increasing the number of grains per unit area (Demarco et al., 2022). Biomass accumulation was described as a trait with small or no changes over time for sorghum (Demarco et al., 2022;Gizzi & Gambin, 2016). However, the plant physiological mechanisms underpinning yield gains over time indicate a better utilization of resources in modern genotypes or hybrids (Ciampitti & Prasad, 2016;Pfeiffer et al., 2019). ...
Retrospective studies are critical to investigate changes in physiological traits related to nitrogen (N) uptake and yield formation. N is a key yield‐limiting nutrient in sorghum (Sorghum bicolor L. Moench), as in most crops, so improving its N internal efficiency (NIE, yield to N uptake ratio) could increase productivity and sustainability. Understanding changes in N efficiency across time linked to carbon (C) economy can provide insights for future breeding targets. This study aims to characterize N and C dynamics (via studying changes in water‐soluble carbohydrates, WSC) of 20 commercial U.S. sorghum hybrids released from 1963 to 2017. Field trials were conducted during the 2018 and 2019 growing seasons in Riley County, KS. Seasonal changes in biomass accumulation, N uptake, and WSC were characterized during both vegetative and reproductive periods. Modern hybrids had greater NIE compared with those from the 1960s. Overall, beyond the yield gain documented for modern sorghum hybrids, the NIE increased at the expense of a reduction in grain N and, in minor proportion, due to increase in the N harvest index (NHI) at maturity for newer relative to older hybrids. Newer hybrids evidenced greater N remobilization from the stover to the grains during the reproductive period. This study demonstrates the physiological mechanisms for an increase in N and C utilization behind yield genetic gain for sorghum hybrids. Future yield gain in sorghum could be pursued by enhancing N uptake to sustain further genetic progress. Nitrogen internal efficiency (NIE) increased during the past six decades for U.S. sorghum. Improvement on NIE was mainly linked to yield gain and dilution in grain N in modern hybrids. Nitrogen remobilization plays a key role in the historical enhancement of NIE in sorghum. Stover N content at maturity decreased over time to sustain grain N demand.
... Grain sorghum (Sorghum bicolor L.) is the fifth-largest cereal crop in the world (Ciampitti and Prasad, 2019), standing out for competitive advantages including high biomass production, grain quality, and yield stability under stress conditions such as drought and high temperatures (Gizzi and Gambin, 2016). Although sorghum possesses these desirable plant traits, the genetic gain in the past decades has been low compared to other crops. ...
... Since the development of sorghum hybrids, sorghum breeding programs have focused on improving the performance of A-and R-lines in a concurrent and complementary mean with the expectation that hybrid combinations between elite inbred lines derived from complementary heterotic groups will maximize heterosis. There is some evidence that this has occurred over the past 60 yr (Assefa & Staggenborg, 2010;Gizzi & Gambin, 2016;Pfeiffer et al., 2019). ...
Genomic selection in maize (Zea mays L.) has been one factor that has increased the rate of genetic gain when compared with other cereals. However, the technological foundations in maize also exist in other cereal crops that would allow prediction of hybrid performance based on general (GCA) and specific (SCA) combining abilities applied through genomic-enabled prediction models. Further, the incorporation of genotype × environment (G × E) interaction effects present an opportunity to deploy hybrids to targeted environments. To test these concepts, a factorial mating design of elite yet divergent grain sorghum lines generated hybrids for evaluation. Inbred parents were genotyped, and markers were used to assess population structure and develop the genomic relationship matrix (GRM). Grain yield, height, and days to anthesis were collected for hybrids in replicated trials, and best linear unbiased estimates were used to train classical GCA-SCA-based and genomic (GB) models under a hierarchical Bayesian framework. To incorporate population structure, GB was fitted using the GRM of both parents and hybrids. For GB models, G × E interaction effects were included by the Hadamard product between GRM and environments. A leave-one-out cross-validation scheme was used to study the prediction capacity of models. Classical and genomic models effectively predicted hybrid performance and prediction accuracy increased by including genomic data. Genomic models effectively partitioned the variation due to GCA, SCA, and their interaction with the environment. A strategy to implement genomic selection for hybrid sorghum [Sorghum bicolor (L.) Moench] breeding is presented herein.
... In addition, this model permitted to remove the environmental effects over each parameter and subsequently measure the genetic progress. For this, BLUPs of hybrid effects were related to their YOR and absolute genetic progress estimates were obtained as the slopes of linear regressions (De la Vega et al., 2007;De Felipe et al., 2016;Gizzi and Gambín, 2016). Relative genetic progress (in % year − 1 ) ...
Sowing date (SD) modifies the environmental conditions during the kernel-filling period as well as during kernel dry down after physiological maturity (PM), particularly for late-sown maize (Zea mays L.) crops that currently cover 50 % of the maize area in Argentina. The main goal of this work was to evaluate breeding effects on kernel filling and kernel desiccation traits in a set of five commercial maize hybrids released by a single breeding program between 1980 and 2016 when grown under contrasting environments in the temperate Central Pampas region. The evolution of kernel weight (KW) and kernel moisture (KM) were assessed. Maximum KW (KW MAX), maximum kernel water content (KWC MAX), kernel filling rate (KFR), kernel filling duration (KFD) and KM at silking+20 days (KM R1+20) and PM (KM PM) were computed together with husks number. Pre-PM kernel desiccation was described using an exponential decay model with k 1 as the proportionality drying coefficient. For the post-PM period, kernel desiccation was modelled assuming that the change in KM in a given period is proportional to the difference between the kernel and the equilibrium moisture contents, where k 2 was the corresponding proportionality drying coefficient. For KW MAX, a genetic progress of 0.26 % year − 1 (p < 0.05) was estimated from 1993 to 2016. This trend was explained by the increase registered in KFD (0.32 % year − 1 , p < 0.01), which was partially compensated by a reduction in KFR (− 0.08 % year − 1 , p < 0.05). No genetic progress was detected for husks number, KWC MAX , KM R1+20 , KM PM , k 1 and k 2 , but introduction of dent germplasm produced an increase in KWC MAX , KM R1+20 and KM PM and a decrease in k 2. KFR and KFD as well as kernel desiccation dynamics were strongly affected by SDs. Breeding effects that extended KFD, together with the broad adoption of late sowings, promote a reduction in k 2 , which must be considered for the correct assessment of trade-offs between drying costs and kernel quality penalization by pests and diseases.
... In our study, the grain-filling rate ranged from 0.56 to 1.34 mg grain/day, while the duration ranged from 30 to 40 days in length (Table 2). Likewise, Gizzi and Gambín (2016) reported no changes in grain weight for hybrids released from 1984 to 2014 and no changes in the duration of the seed filling period over time. This demonstrates that, as for maize (Otegui et al., 2015), there has not been a tradeoff between grain number and weight over time with yield selection in sorghum. ...
... Аналiз окремих сучасних сортiв та сучаснi досягнення геномної селекцiї ставлять новi вимоги щодо використання мiсцевих ресурсiв та локальних особливостей у межах конкретного агроклiматичного, агроекологiчного району [6,8,14,17]. Перш за все це стосується таких ознак як якiсть, наявнiсть окремих харчових цiнних компонентiв, генетично обумовлена стiйкiсть до хвороб та шкiдникiв для усунення пестицидного навантаження. ...
В наш час використання локальних генетичних ресурсів та відновлення високого рівня генетичного різноманіття і використання адаптивного потенціалу місцевих генотипів. Так як таки генотипи більш пристосовані до локальних екологічних умов зростання. Все це актуалізує наші дослідження. Мета публікації – в умовах північного Степу України проаналізувати мінливість основних параметрів врожайності та якості зерна, межі адаптивності існуючого матеріалу, а також прояв в комплексі господарсько-цінних ознак для 14 сучасних сортів пшениці м'якої озимої. Дослідження проведено упродовж 2017-2019 років в умовах Навчально-наукового центру Дніпровського державного аграрно-економічного університету. З використання класичних методик виконано визначення в польових умовах врожайності та параметрів її структури, лабораторний аналіз показників седиментації, вмісту білка та клейковини. Отримано дані щодо можливості формування високої врожайності в наших умовах при наявності не лише високої ваги зерна з колосу та маси тисячі зерен, але й без перевищення стандарту за цими показниками. Також отримано зерно високої якості (достатній вміст білку та клейковини) як при підвищенні врожайності так і підвищення врожайності та якості зерна в порівнянні зі стандартом разом. Встановлено, що в екологічних умовах Північного степу України за комплексом ознак якості зерна та врожайності самим перспективним слід вважати сорт АС Маккінон, а також варто використовувати сорти Носівчанка, Овідій, Мілена, що здатні формувати врожайність вищу за стандарт при збережені якості зерна на його рівні. З метою поліпшення якості зерна при одночасному збережені врожайних показників на рівні стандарту перспективними є сорти Панна та Акорд. Провідними еколого-агрономічними особливостями цих сортів, є те що їх висока зернова врожайність формується перш за все за рахунок маси тисячі зерна та зерна з головного колосу, параметрів кількість продуктивних стебел з метру квадратного та маси зерна з метру квадратного метру. Набули подальшого розвитку уявлення щодо можливостей формування основних агрономічно-цінних ознак. Виявлено нові цінні донори цих ознак для селекційних досліджень.
... Studies in crops such as maize (Zea mays L.) have reported high genetic gains in yield with values ranging between 0.80 and 1.74% yr −1 in the United States, Argentina, and Brazil (Borras & Vitantonio-Mazzini, 2018;Fischer et al., 2014;Parra et al., 2020). In sorghum (Sorghum bicolor L. [Moench]), the genetic gain in yield is lower than maize with an average of 0.08% yr −1 in the United States and Argentina (Gizzi & Gambin, 2016;Pfeiffer et al., 2019). Annual genetic gains in wheat (Triticum aestivum L.) cultivars were between 0.48 and 1.23% yr −1 in cultivars released ...
To respond to the high demand for cotton (Gossypium hirsutum L.) fiber, constant enhancements by breeding or management are required. The study of the genetic progress shows the changes in traits over the years, providing information about the real contribution and benefits of breeding and management efforts. In order to estimate the genetic progress of nine upland cotton cultivars for the lowlands agroecology of Venezuela released from 1963 to 2010, evaluations were performed in three locations in Venezuela during 2012 and 2013. Lint yield (LY), boll weight (BW), number of seeds per boll (SB), seed index (SI), lint percent (LP), plant height (PH), and stem diameter (SD) were measured. Combined analysis of variance showed differences (P ≤ .01) among the cultivars, environments, and their interaction for all traits, except for SB and SI. All variables have increased for the period evaluated, except for PH that showed a gradual decrease of 0.12% year–1. LY increased by 10.06 kg ha–1 year–1 or 0.29% year–1, which is a total of 503 kg ha–1 in 50 years. A reduction of PH (0.19 cm year–1) was observed, meanwhile BW (0.0022 g year–1), SB (0.0029 year–1), SI (0.0038 g year–1), SD (0.0013 cm year–1) and LP (0.0071% year–1) increased 0.04, 0.01, 0.04, 0.08 and 0.02% year–1, respectively, in the same period. These results indicate that the introduction of genotypes with divergent backgrounds and development to specific agroecologies have contributed to constant genetic progress in cotton cultivated in Venezuela. This article is protected by copyright. All rights reserved Lint yield (LY) and plant height were the traits with significant changes in the past 50 years A continuous increase of LY was observed with an average of 0.29% per year The genetic gains of LY, is the result of cultivars selected across target environments
... According to Benbelkacem (2014) who reviewed the evolution of Algerian durum wheat breeding from the beginning of the past century, more than 24 different historical eras indicated that substantial genetic gain was achieved because of varietal replacement (Battenfield et al., 2013;Fischer et al., 2014). Realized genetic gain is often greater in well managed than under poorly managed growth conditions, which seems to justify the persistent cultivation of traditional cultivars under harsh environments (Gizzi & Gambin, 2016;Wang et al., 2017). , comparing ancient wheat varieties to modern ones, noted that the old varieties were tall, late and less productive. ...
The existing work aimed at evaluation of 58 old and modern durum wheat grown under south Mediterranean conditions. The experiment was conducted in a randomized complete block design at two locations (ITGC-AES of Setif and Khroub, Algeria) considered during two successive winter seasons of 2015/16 and 2016/17. Results indicated that, averaged across seasons and locations, modern varieties outperformed older varieties in terms of grain yield, spike number, spike weight, number of kernels per square meter, harvest index, spike fertility and stay green. Old varieties surpassed the modern ones in terms of straw yield, lateness, tallness and flag leaf area. Whereas, modern varieties were stress tolerant and more responsive to improved growth conditions, showing agronomic stability type. Old varieties were characterized by a minimal responsiveness to improved environmental conditions, stress tolerance, and biological stability type. Pearson’s correlation coefficients and path analyses indicate that, in both sources of germoplasm, the strong influence of biomass, spike number, spike fertility and harvest index on grain yield. Physiological traits had negligible direct effects and small indirect effects via biomass, spike number and harvest index. Lastly, principal component analysis revealed that old varieties represent an important gene pool for important traits among which plant height and straw yield. Furthermore, the differences between both sources of germoplasm can be usefully used in breeding program (Gene-bank) to enhance yield potential, stability and resilience to changing climate of the future varieties.
... Sorghum is currently cultivated in 105 countries, with an average total area of 43.69 million ha and yearly production of 66.03 million tons of grains from 2014 to 2016 (FAO, 2017). Genetic improvement is recognized as a key approach underpinning the sorghum grain yield increase recorded in China (Li et al., 2018), United States (Pfeiffer et al., 2019), and Argentina (Gizzi and Gambin, 2016). In particular, heterosis has been used to obtain steady increases in grain yield for more than 90 years (e.g., Duvick, 2005), despite no scientific consensus yet reached on the genetic basis of heterosis in plants (Blum, 2013). ...
Sorghum [Sorghum bicolor (L.) Moench] is a high-yielding C4 crop used not only to produce grains for food, feed, and industrial uses but also biomass (i.e., leaf and stem) for biofuel production. To take better advantage of its heterosis for both grain and biomass dual-purpose use, the combining ability of 34 cytoplasmic male sterile lines (female) were tested with 3 cytoplasmic male fertile restore lines (male) using the North Carolina design (NCII) at Zhuozhou (Hebei province) and Jiexiu (Shanxi province) in northern China for two years (2017 and 2018). The hybrids exhibited a grain yield of 0.3 ~ 14.0 t ha − 1 and had an aboveground biomass yield (AGBY) of 9.6 ~ 109.9 t ha − 1 across both sites in 2017 and 2018. The genotype and site × genotype interactions significantly affected the yield and agronomic traits. With respect to their grain and biomass dual-purpose use, the tested 34 female lines revealed that plant height, gravity center height, productive tiller rate, and harvest index were strongly general combining ability (GCA) sensitive. Stem width, days to maturity, AGBY, and grain width were medium GCA-sensitive; and grain yield, 100-grain weight, days between heading and maturity, and grain bulk density were weakly GCA-sensitive. The GCA effect on grain yield was positive and significantly correlated with productive tiller rate, AGBY, and harvest index. The GCA effect on AGBY had a positive, significant correlation with plant height, gravity center height, productive tiller rate, and days to maturity; but the effect was negatively correlated with 100-grain weight and grain width. For tested traits, the additive gene effects strongly predominated over the non-additive genes for tested traits. Plant height was the most GCA-sensitive trait and the most important for biomass production. Female lines AMP418, AMP431, AMP434, AMP443, AMP495, AMP496 and the male line X097 were selected as being high-GCA effect germplasm. These selections from newly introduced cytoplasmic male sterile lines hold promise for accelerating the genetic improvement of sorghum for its dual-purpose use as grain for food and biomass for biofuel.
... A positive relationship was found between grain set efficiency and the period of years of introduction of the selected hybrids ( Figure 2). Hybrids with greater yield are able to set more grains per unit of reproductive biomass at flowering (Gizzi and Gambin, 2016). In parallel, an increase of the size of the panicle was documented across years ( Figure 3) contributing to the explanation of an increase in the number of grains per panicle. ...
For the last decades, sorghum (Sorghum bicolor L. Moench) improvement in the United States (US) has been related to targeted modifications in genotype, environment, and management (G × E × M) combinations. Retrospective studies are relevant to document changes in the phenotype associated to breeding process and to explore alternatives to improve yield and its physiological associated traits. This study aims to characterize yield changes over time for hybrids with different year of release. Field trials were conducted during 2018 and 2019 growing seasons in eight environments/site-years across the states of Kansas and Texas including 20 grain sorghum hybrids released between 1963 and 2017. Grain yield was measured across all hybrids and environments. Detailed physiological descriptors were measured in one of the environments including grain filling, grain set efficiency (grains g-1) at flowering, panicle length, and dynamics of water-soluble carbohydrates (WSC) during the reproductive period. Overall sorghum grain yield improvement was 0.4 bu/a/year (P < 0.005). Grain set per unit of reproductive biomass at flowering was positively associated with the hybrid’s year of release, explaining the increases in grain number. Panicle size increased in newer hybrids, thus, supporting the reported changes in grain number per unit area. Modern sorghum hybrids displayed greater WSC remobilization during the reproductive period (P < 0.05). However, further research on sorghum’s WSC dynamics is needed for understanding its contribution to yield improvement.
... The rates of genetic gain are often greater in well-fertilized, well-watered crops than in their counterparts with water and/or nutrient deficiencies (Austin et al., 1980;Slafer and Andrade, 1989;Brancourt-Humel et al., 2003;De Vita et al., 2007;Giunta et al., 2007;Barraclough et al., 2010;Tian et al., 2011;Gizzi and Gambin, 2016;Wang et al., 2017). In-furrow fertilization with nitrogen, phosphorus, sulfur, and zinc can improve early-season wheat tillering, biomass production, and yield (Rodríguez et al., 1998;Rodríguez et al., 1999;Valle et al., 2009;Lollato et al., 2013). ...
Plant breeding has increased the yield of winter wheat (Triticum aestivum L.) over decades, and the rate of genetic gain has been faster under high fertility in some countries. However, this response is not universal, and limited information exists on the physiological traits underlying the interaction between varieties and fertilization. Thus, our objectives were to identify the key shifts in crop phenotype in response to selection for yield and quality, and to determine whether historical and modern winter wheat varieties respond differently to in-furrow fertilizer. Factorial field experiments combined eight winter wheat varieties released between 1920 and 2016, and two fertilizer practices [control versus 112 kg ha-1 in-furrow 12 -40-0-10-1 (N-P-K-S-Zn)] in four Kansas environments. Grain yield and grain N-removal increased nonlinearly with year of release, with greater increases between 1966 and 2000. In-furrow fertilizer increased yield by ~300 kg ha-1 with no variety × fertility interaction. Grain protein concentration related negatively to yield, and the residuals of this relationship were unrelated to year of release. Yield increase was associated with changes in thermal time to critical growth stages, as modern varieties had shorter vegetative period and longer grain filling period. Yield gains also derived from more kernels m-2 resultant from more kernels head-1. Historical varieties were taller, had thinner stems, and allocated more biomass to the stem than semidwarf varieties. Yield gains resulted from increases in harvest index and not in biomass accumulation at grain filling and maturity, as shoot biomass was similar among varieties. The allometric exponent (i.e., the slope between log of organ biomass and log of shoot biomass) for grain increased with, and for leaves was unrelated to, year of release. The ability of modern varieties to allocate more biomass to the kernels coupled to an early maturity increased grain yield and grain N-removal over time. However, increases in grain yield were greater than increases in grain N-removal, reducing grain protein concentration in modern varieties.
... Formation of soft, milky grains after anthesis was observed as start of grain filling. Physiological maturity was recorded after visual observations of black layer in five of ten consecutive plants (van Oosterom and Hammer 2008;Gizzi and Gambin 2016) from basal panicle positions ( Gambin and Borras 2005) in each of the experimental planting rows. ...
Water productivity (WP) is becoming a key issue in understanding the relationship between water availability and rainfed sorghum (Sorghum bicolor L. Moench) yields in agricultural systems across sub–Saharan Africa. The objective of this study was to determine water productivity of three sorghum genotypes under different environmental conditions. Three sorghum genotypes, a hybrid (PAN8816), a commercial open-pollinated variety (Macia) and a landrace (Ujiba) were planted at two sites (Ukulinga and Mbumbulu) in South Africa during 2013/2014 and 2014/2015. High clay content in Mbumbulu lowered plant available water in the soil compared to Ukulinga. Sorghum adapted to low water availability by significantly (P < 0.05) lowering plant growth (green leaf number, plant height and canopy cover), crop physiology (chlorophyll content index and stomatal conductance), biomass and grain yield. Ujiba and PAN8816 genotypes hastened phenological development, whilst Macia delayed phenological development in response to low water availability. Total and grain WP were lower at Mbumbulu (14.93 and 7.49 kg/ha/mm) relative to Ukulinga (21.49 and 11.01 kg/ha/mm), respectively. Results showed that Macia had significantly higher (P < 0.05) WP (10.51 kg/ha/mm) relative to PAN8816 (9.34 kg/ha/mm) and Ujiba (7.90 kg/ha/mm). Lack of significant genotypic differences in grain WP highlights that all three genotypes are equally suitable for production under sub–optimal and dryland conditions.
... While a number of studies have investigated variation in plant or canopy attributes linked to resource capture and growth and their relation to grain number (Blum et al., 1997;van Oosterom and Hammer, 2008;Hammer et al., 2010;George-Jaeggli et al., 2013), studies associated with P R and E G are limited Aisawi et al., 2015;Slafer et al., 2015). Sorghum grain yield improvement in Argentinean commercial hybrids has been associated with increased E G (Gizzi and Gambin, 2016), demonstrating the trait value. ...
The genetic basis of grain number determination in sorghum [Sorghum bicolor (L.) Moench] was studied based on canopy growth traits. Traits were crop growth rate (CGR) around flowering, plant reproductive biomass partitioning (PR) to the panicle, and grain-set efficiency (EG) per unit of accumulated panicle biomass. Previous evidence has shown that these traits vary across commercial germplasm and that PR and EG are genotype-specific traits with low environmental effects. Our hypothesis was that PR and EG are highly heritable traits correlated to grain number (and yield) for which environmentally consistent quantitative trait loci (QTL) could be detected. Studied recombinant inbred lines (RILs) showed important variation in yield, grain number per square meter, time to anthesis, plant height, CGR, PR and EG, and growth environments created significant genotype × environment interactions for most. Variability in grain number per square meter was significantly correlated with PR (p < 0.001) and EG (p < 0.001) but not with CGR (p > 0.05). Heritability estimates for PR and EG were larger than estimates for CGR, grain number per square meter, or yield. A multitrait, multienvironment approach over CGR, PR, and EG identified 12 QTL (LOD ≥ 2.5), explaining 21 to 36% of observed trait variability. No QTL were detected for CGR, while two and one environmentally consistent QTL were found for PR and EG, respectively. Results highlighted relevant information that could be potentially exploited in breeding programs. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA.
... Ordinary least squares regressions were calculated to estimate average genetic gain over time. A quantile regression at the 90th percentile was used to estimate genetic gain for the top 10% of cultivars across years of release (de la Vega et al., 2007;Gizzi and Gambin, 2016). The genetic gain for any of the evaluated traits was expressed both in absolute and relative change per year. ...
Genetic progress is assessed to estimate its contribution to on-farm yield increases and to identify traits that have been improved over some period of time. Although Argentina is a major soybean [Glycine max (L.) Merr.] producer, there is limited information about genetic progress in this system. Argentinean soybean cultivars were developed from US commercial cultivars. Because the genetic base of US cultivars is narrow, it would be expected that genetic progress in Argentina to be slower than in the United States. We assessed the genetic gain for yield and related traits in cultivars released in Argentina from 1980 to 2015. One hundred and eighty-one cultivars belonging to maturity groups (MGs) III, IV, and V were evaluated in three environments in the northern pampas from Argentina. Genetic gain in yield was 43 kg ha⁻¹ yr⁻¹ and was not different across MGs. Relative genetic gain was 1.1% yr⁻¹, similar to reports from the United States or Brazil. Newer cultivars from MGs III and IV had increased days to maturity, while cultivars from MG V showed the opposite trend. Vegetative period was also reduced in newer cultivars from MGs IV and V. Seed protein concentration was reduced over the years. Genetic progress explained 50% of total on-farm yield increase. Results from this experiment showed that breeding programs in Argentina were able to attain a similar genetic gain to the United States even though the starting parents were only a few US cultivars selected from an already narrow genetic base. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA.
... Hence, the characterization of commercially available hybrids of sorghum is required to be able to choose those with the most suitable properties for each application, with the most important selection criteria used for grain sorghum by breeders being the direct measurement of grain yield and grain yield stability. Although selection is commonly based on performance trials across a wide number of sites and year [12], further characterization of sorghum hybrids is essential to fully develop their potential. ...
This work analyzed the physical, chemical, and thermal properties of sorghum flour and the relationships among these, in order to evaluate its suitability for the development of food products. Sorghum flour was obtained through roller dry milling from 20 commercial hybrids grown in Argentina with the average chemical composition of the samples being: 0.68% ash, 3.67% fat, 12.21% protein, 83.45% total carbohydrates, 79.77% starch (amylose 26.6%), and 34.9 mg of tannic acid per 100 g of flour. A high degree of variability among evaluated properties was found, particularly in the pasting properties peak viscosity (2809–5184 mPa/s), breakdown (1169–3170 mPa/s), and final viscosity (3030–4401 mPa/s) with onset temperature (To) and gelatinization enthalpy (ΔH) varying between 66.8 and 72.6°C, and 5.38 and 8.48 J/g, respectively. A principal component analysis demonstrated that the grain color did not influence the chemical composition of the flour. Cluster analysis permitted the separation of flour into three different groups with different thermal and physicochemical characteristics, and enabled the selection of hybrids. Thus, sorghum flour is a versatile ingredient and can be used in several food and non-food applications.
For mature breeding programs, maintaining genetic variation in elite germplasm requires a continual assessment of the most efficient methods to maximize functional genetic variation while improving productivity. This research assessed the relative value (defined as population means and variances) derived from elite germplasm exchange between distinct public breeding programs. Ten elite A‐ and R‐lines from Texas A&M and Kansas State sorghum breeding programs were crossed in a factorial design to generate 100 hybrids. Hybrid combinations were grouped to represent hybrids within and across programs. Grain yield, plant height, and days to anthesis were measured in ten environments over two years. Combining abilities and their interactions with the environment were assessed. Combined analysis detected significant effects for all traits, but genetic effects for grain yield were not consistently significant within each group of hybrid combinations. Hybrids derived from only Texas inbreds had limited genetic variation for grain yield but the highest mean of all four groups; hybrids derived from only Kansas inbreds produced moderate genetic variation but lower grain yield potential. Maximum genetic variation for grain yield and plant height occurred when Kansas A‐lines were crossed to Texas R‐lines, whereas hybrids between Texas A‐lines and Kansas R‐lines maximized variation for days to antheses. Results demonstrated the potential benefit from crossing elite inbred parents derived from distinct breeding programs to increase genetic variation and enhance agronomic performance. This article is protected by copyright. All rights reserved Maintain/increase selectable genetic variation in mature breeding programs is a major challenge Crosses between elite lines from distinct breeding programs can increase genetic variation Elite lines exchange among breeding programs can foster cooperation amid public institutions
Sorghum (Sorghum bicolor (L.) Moench) is one of the most resilient crops grown in the tropical, subtropical, or temperate regions of Africa, Asia, Oceania, and Americas. Globally, the top five worldwide sorghum producers are USA, Nigeria, Sudan, Ethiopia, and India. Sorghum production area is declining and shifting to lower productivity regions or soil types; however, annual productivity gains continue in excess of 8.7 kg/ha due to genetics alone and up to 50 kg/ha when genetics and management combinations are considered. Growers prefer sorghum because of the low risk and reliable production especially in low-input production systems but often switch to cotton, maize, or soybean crops rather than intensify sorghum production. Further management (agronomic practices) and breeding efforts should be dedicated to increasing attainable yield and reduce the yield gap (potential minus actual yields). The latter can be achieved by improving the understanding of the complexity of the genotype (G) by environment (E) by management (M) interaction (G × E × M). A summary presenting best management (e.g., planting date, seeding depth, cultivar-/hybrid-type selection, row spacing, plant density, and crop rotations) of modern sorghum hybrid traits across environments could provide insights for yield improvement. This chapter provides an update on the state of the art on the sorghum management systems and production technology under diverse environments across the globe. We identify that sowing date and maturity group remain the most important management and genetic trait combinations for sorghum systems due to changes in production technologies, climate, and increased production in marginal areas of different continents.
Sorghum is the dietary staple for millions of people living in the subtropical and semi-arid regions of the globe. Its cultivation around the world is spread over diverse agro-ecosystems. In almost all the sorghum-growing regions, the grain yield levels have been enhanced over the years because of improved cultivars with higher nutrient response and better crop management practices. In every sorghum improvement program, yield and adaptation are the primary objectives for improvement. Wide genetic diversity is available in the cultivated Sorghum bicolor, as reflected in its five basic races, viz., bicolor, kafir, guinea, caudatum, and durra, and their ten intermediate races. The Zera-zera (an intermediate race between caudatum and guinea) landraces from Ethiopia and Sudan have proved to be useful sources for many traits such as excellent grain quality, high grain yield potential, tan plant, resistance to leaf diseases, and desirable plant type. Despite the considerable diversity in the available germplasm, very few germplasm lines have been utilized in the breeding for yield and adaptation so far. The diversity among the five basic races needs to be exploited to broaden the genetic base to produce cultivars with higher yield and adaptation for sustainable production.
The main physiological processes associated with soybean [Glycine max (L.) Merr.] genetic yield progress in central temperate Argentina are largely unknown. This knowledge is critical to identify opportunities to accelerate yield gains via trait‐based hybridization. Our objectives were to: (a) evaluate the influence of biomass accumulation vs. harvest index (HI) in explaining genetic progress, and (b) assess the role of radiation and/or N capture and use efficiency (RUE and NUE, respectively) as drivers of biomass accumulation. We tested 173 cultivars released from 1980 to 2014 in two high‐yielding environments. Additionally, a crop modeling exercise was performed to demonstrate the physiological perception that any genetic increase in RUE would only translate into more yield if there is enough water for the realization of that RUE. Observed genetic progress was 42 kg ha−1 yr−1, or ∼1% yr−1, and was mostly explained by increased aboveground biomass accumulation. This higher biomass of modern cultivars was associated with increased RUE and total N uptake. This suggests that, if residual genetic variation is still present in current soybean cultivars, future genetic improvements should focus on further improving N uptake to increase RUE. Increases in RUE are associated with increased stomatal conductance and water use. Therefore, it would be expected that genetic progress is faster in environments with increased rainfall. Our modeling exercise was consistent with this hypothesis and showed that soybean genetic progress simulated in different locations within a rainfall gradient was positively associated with cumulative seasonal precipitation.
The genetic yield potential in grain sorghum [Sorghum bicolor (L.) Moench] hybrids has increased at a slower rate than other cereal crops. While there are many reasons for this lag, increasing heterosis through broadening genetic distance between parents is commonly hypothesized as a mechanism to boost the rate of gain. To assess the relationship between heterotic groups in sorghum, a panel of 435 inbred lines from the Texas A&M program was genotyped using Genotyping-By-Sequencing (GBS). Lines were divided into three groups through K-means clustering based on genetic similarity. Distinct groups of B-lines, R-lines, and forage lines were observed, but they were not highly divergent from one another. In both elite germplasm and a large panel of sorghum lines, less diversity was observed among B-lines than R-lines. From the panel of 435 inbreds, a subset of 24 elite grain-type lines was chosen and crossed to produce 52 hybrids. Hybrids and parental lines were evaluated in four environments for grain yield, plant height, days to flower, and panicle exsertion. Genetic similarity among elite inbred parents of hybrids evaluated ranged from 0.632 to 0.792. For all traits, significant mid-parent heterosis was observed; however, correlations between mid-parent heterosis and genetic similarity were low to non-significant. GBS-based genetic similarity is not a good predictor of heterosis or hybrid performance among elite Texas A&M sorghum inbreds. However, some parental-inbred performance measurements may be predictive of hybrid performance.
Argentinean current sorghum management is similar across the entire temperate region, and no environmental characterization is assisting breeding and management decisions. Crop growth and development simulation models are a valuable tool for generating this characterization. Our study calibrated and validated APSIM-sorghum for our genetics and production environments, and used it to characterize the main water and heat stress patterns at our temperate central region. The calibration and validation provided accurate phenology, biomass, and yield estimations. Long-term weather records (44–61 years per site) and soil data were used to simulate the seasonal drought patterns at seven representative sites across the region. Clustering analysis identified three major drought environmental types (ENVT): (i) a pre-flowering drought stress, showing large occurrence frequency (39%), (ii) a low terminal drought stress, showing similar frequency (38%), and (iii) a grain-filling drought stress, showing lower frequency (23%). The most frequent ENVT at individual sites agrees with the spatial distribution of annual rainfall. However, most sites evidenced variable frequency of all ENVT. Flowering heat stress (>33 °C) showed an intermediate occurrence frequency (20–50%) only at lower latitudes, and was independent of drought ENVT. Defined ENVT helped explain observed genotype x environment (GxE) interactions for yield in an independent data set, showing they have practical implications for optimizing breeding and management strategies across the region of interest. Grouping sites of similar frequency can help to handle the spatial variability when defining these strategies, but dealing with seasonal variability will be challenging in the context of no predominant ENVT.
Trigo pan y cebada cervecera son los principales cereales de invierno sembrados en Argentina, en consonancia con su relevancia a nivel mundial. Durante el último quinquenio, el rendimiento medio logrado a nivel productivo en Argentina ha sido para trigo de 2972 kg ha-1 y para cebada de 3596 kg ha-1, un -9% y +24% respecto al rendimiento medio mundial para el mismo período en cada cultivo. Desde 1960 a la actualidad, el aumento de rendimiento logrado en Argentina presentó una tasa de 32 kg ha-1 año-1 para trigo y de 51 kg ha-1 año-1 para cebada. Alrededor de un tercio del aumento de rendimiento logrado a campo estuvo dado por el progreso genético, en ambos cultivos, pero con fuertes variaciones a lo largo de los años. Tanto en trigo como en cebada el aumento de rendimiento por progreso genético estuvo asociado a un aumento en el número de granos m-2, sin una tendencia definida en el peso de los granos. Las deficiencias nitrogenadas, las altas temperaturas, y los eventos de anegamiento son algunos de los estreses abióticos a los que están expuestos ambos cultivos en condiciones de campo. En el presente trabajo se describe el impacto de dichos estreses sobre la definición del
rendimiento en trigo y cebada, en base a resultados propios obtenidos por los autores del presente trabajo. El número de granos logrados por m2 fue el componente numérico que explicó el rendimiento independientemente de la especie y de la naturaleza del estrés. Dado que la definición del número de granos queda supeditada a la condición ambiental alrededor de antesis, el uso de modelos de simulación es una herramienta para evaluar cuándo ocurrirá dicho evento.
Estimating genetic gains in sorghum [Sorghum bicolor (L.) Moench] is necessary to assess whether the current rates of improvement will meet future production demands. The current study was conducted to determine the rate of genetic gain in yield and associated traits over the commercial hybrid era using sorghum germplasm from the Texas A&M sorghum breeding program and a US sorghum seed company. From the Texas A&M AgriLife program, 60 hybrids that represented a 50-yr span of hybrid breeding were grown and evaluated in five environments across Texas in 2016. In a separate set of trials, 14 commercial hybrids representing a similar timespan were evaluated in three Texas environments in 2016. In both programs, grain sorghum yields increased 0.008 t ha⁻¹ annually over their respective timespans. Traits that increased over time included yield potential per plant, heterosis, test weight, panicle size, and grain number per panicle, whereas leaf angle, days to maturity, plant height, and yield stability demonstrated little to no change. Overall, ~60% of total yield gains in US sorghum production are attributed to genetic improvement through sorghum breeding. Compared with other major US field crops, the rate of genetic gain in sorghum has been slower, presumably due to a combination of factors, which include continually shifting production environments, changing priorities in traits, reduced research investments (compared with other crops), and less-than-optimized heterotic groups. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Effective plant improvement depends on understanding grain yield genotype by environment (G×E) interactions. Studies focusing on more heritable (secondary) traits provide a way for interpreting the nature of these interactions and assist selection by adapting hybrids to specific adaptation patterns. The objective of our study was to explore some specific traits to help describe G×E interactions for yield in grain sorghum. A set of 22 representative hybrids were grown at eight different environments varying mainly in water and nitrogen availability. Studied traits were yield, phenology (time to anthesis and grain-filling duration), numerical yield components (grain number and individual grain weight) and physiological components (biomass at maturity and harvest index). The G×E interaction to G component variance represented 3.48 for grain yield, 1.03 for grain-filling duration, 0.87 for biomass at maturity, 0.71 for time to anthesis, and less than 0.5 for the rest of the traits. Although the G×E interaction for yield was large, the relative genotypic contribution of most studied traits suggests that G×E interaction is not a major impediment for attaining high selection responses to these traits. Pattern analysis applied to G×E best linear unbiased predictors defined three genotype and three environmental groups. Environments were grouped suggesting different water stress levels during early or pre-flowering stages, whereas genotype groups depicted different yield responses across environmental groups. Phenology differences among genotypes explained a large portion of the G×E interaction throughout its influence on grain weight. Late flowering genotypes performed poorly in terms of grain weight and yield across all environments, showing that these materials are not the best option for our production system. Longer grain filling contributed to grain weight and yield at environments with low stress levels, particularly when combined with intermediate or short maturity. Early materials contributed to grain weight and yield at the highest stressful environments. We provide useful information to sorghum breeders at temperate environments, and described secondary traits that could assist selection at particular environments.
The global wheat (Triticum aestivum L.) growing area under irrigation has risen to approximately 20%. However, future availability and quality of irrigation water is likely to decline due to competition from the needs of the expanding population combined with the effects of climatic change. Recent genetic improvements of the yield of irrigated spring wheat lines reported by CIMMYT have been associated with significantly higher biomass, suggesting that either crops are becoming more water use efficient or are extracting more water from their environment. Water uptake characteristics of eight CIMMYT spring bread wheat cultivars-released during the period between 1950 and 2009-were measured in three contrasting irrigation regimes in northwestern Mexico during 2009/2010 and 2010/2011 and compared with crop growth. Increases in yield and biomass of genotypes were associated with additional water uptake in all environments whilst the water use efficiency for yield and biomass production was unchanged across cultivars but increased as a main effect of reduced water supply. Modern cultivars showed increased ability to extract moisture from deeper soil profiles (60-120 cm) especially during grain filling, associated with higher stomatal conductance in the fully irrigated environment and lower canopy temperatures in all environments. Expression of C isotope discrimination was progressively lower with increasing water stress. Results indicated increased water uptake by roots especially from deeper soil profiles allowing greater water harvest.
This paper addresses the question of whether there has been an increase in yield potential of maize (Zea mays L.) hybrids released in the north-central United States since the advent of the “Green Revolution” that began in the late 1960s. Because there are few published data about hybrid growth rates and yield-determining plant traits when grown at yield potential levels, we attempt to address this issue indirectly by evaluation of maize breeding efforts, changes in plant traits of commercial hybrids, and by comparison of statewide average yield trends and yield trends in sanctioned yield contests. On the basis of these sources of information and a definition of yield potential as the yield that can be achieved with an adapted hybrid when grown without obvious stress of any kind, we found that there is conflicting evidence to support the hypothesis that maize yield potential has increased. We recommend experimental approaches to quantify and investigate the determinants of maize yield potential in the north-central United States and for use in breeding hybrids with greater yield potential.
Key message:
Long-term yield trends have genetic and non-genetic components which may be dissected by a linear mixed model with regression terms. Disease-resistance breakdown must be accounted for in the interpretation. Long-term yield trends of crop varieties may be studied to identify a genetic trend component due to breeding efforts and a non-genetic trend component due to advances in agronomic practices. Many such studies have been undertaken, and most of these inspect trends either by plotting means against years and/or by some kind of regression analysis based on such plots. Dissection of genetic and non-genetic trend components is a key challenge in such analyses. In the present paper, we consider mixed models with regression components for identifying different sources of trend. We pay particular attention to the effect of disease breakdown, which is shown to be confounded with long-term genetic and non-genetic trends, causing an over-estimation of genetic trends based on long-term yield trial data. The models are illustrated using German multi-environment trial data on yield, mildew and Septoria leaf blotch susceptibility for winter wheat and yield, mildew and net blotch susceptibility for spring barley.
In the present study we tested how assimilate availability per kernel at different grain-filling stages may affect maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) individual kernel weight (KW). These two species have shown a contrasting KW response to increased assimilate availability at similar seed developmental stages. Plant growth rate (PGR) per kernel was used to estimate the assimilate availability per kernel at two stages: around the early grain-filling period when kernel number per plant is also being established, and around the effective grain-filling period. We tested 3 commercial genotypes from each species, and modified the PGR by thinning or shading the stand at different developmental stages. In both species, each genotype showed a particular relationship between PGR around flowering and kernel number, which gave a range of responses in the PGR per kernel set around flowering. Final KW always increased whenever PGR per kernel around flowering was enhanced. Only sorghum showed a consistent KW increase when PGR per kernel during the effective grain-filling period was enhanced. Results confirmed that increasing assimilate availability per kernel will affect maize kernel size only if the potential set early in development is altered. Most important, we showed that linking specific KW sensibility across species at different seed developmental stages using a simple estimate of assimilate availability per seed (i.e. PGR per kernel) at each grain-filling stage helped explain most of the explored genotypic and environmental variability in final kernel size.
Grain yields of dryland (nonirrigated) grain sorghum [Sorghum bicolor (L.) Moench], a major crop in the southern Great Plains, more than tripled in studies at the USDA-ARS Conservation and Production Research Lab., Bushland, TX, during the period from 1939 to 1997. Our objectives were to document the yield increases that occurred and to determine factors primarily responsible for the yield increases. Factors evaluated were annual precipitation, growing-season rainfall, soil water content at planting, soil water use, growing-season evapotranspiration, and year of record. For the report, we assembled 502 treatment-years of grain yield data from 37 studies. For the 1939-1997 period, grain yields increased about 50 kg ha(-1) annually. Yields increased 139% during the 1956-1997 period, with 46 of those percentage units resulting from use of improved hybrids, based on results of a uniformly managed 40-year study. The remaining 93 percentage units for that period were attributed to other factors, primarily to soil water at planting. Increases in soil water at planting resulted from changes in management practices with time, mainly the adoption of improved crop residue management practices after about 1970.
Large and regional genotype x environment interactions can be a major impediment to sunflower (Helianthus annuus L.) genetic progress in Argentina, where yield improvements have slowed since the mid-1990s. Previous studies in the central subregion show that oil yield gains were maintained for the last 20 yr and contributed to counteracting a decline in agronomic quality of the sunflower area. In this study, mixed models, quantile regression, and pattern analyses were applied to three long-term (18 yr) multienvironment datasets (67 sites) to show that: (i) in high-yielding hybrids, oil yield has increased linearly by 6.7, 10.5, and 6.2 kg ha(-1) yr(-1) over 25 yr in the northern, central, and southern sub-regions, respectively; (ii) selection for specific adaptation to the central region did not improve oil yield in northern environments (consistent with previous pattern analysis-based predictions), nor in the southern region, suggesting that the south is a third mega-environment; (iii) the central subregion had the greatest, most consistent genetic gain; (iv) while the relative regional responses of hybrid groups were similar for oil concentration and grain yield, there was strong hybrid x region crossover for relative responses of time to flowering; and (v) the merger of the original gene pools via breeding for oil yield reduced the original range on phenological responses within subregions and produced different maturity types for each region.
To assess the progress made in modern breeding of open-pollinated sorghum cultivars, 24 contemporary and improved sorghum cultivars from ICRISAT (International Crops Research Institute for the Semi-Arid Tropics, India) were compared with 40 sorghum landraces collected in Ethiopia. The experiment was performed at Bet Dagan, Israel, in 1988 under near-potential (dripirrigated) and dryland (stored soil moisture) growing conditions. Data on phenology, biomass, harvest index, grain yield and its components were collected. ‘Drought susceptibility index’ (S) was calculated for each genotype as the reduction in yield from irrigated to dryland conditions relative to the mean reduction for all genotypes.
On average, cultivars produced about three- to fourfold more grain than landraces. Cultivars had the same mean growth duration and biomass but were 40% (irrigated) to 27% (dryland) shorter in mean plant height than landraces. This yield advantage was fully accounted for by a proportionately greater mean kernel number per panicle and harvest index, irrespective of the water regime. ‘Drought susceptibility index’ was near average for all cultivars and much more variable among landraces. Dryland yield became progressively dependent on the yield potential as the yield potential was genetically improved in the cultivars.
It was concluded that, irrespective of the water regime, the large yield improvement in modern open-pollinated cultivars of sorghum, as compared with landraces, has been achieved only through greater dry matter partitioning to the panicle accompanied by a reduction in plant height. The genetic improvement of yield in open-pollinated cultivars and hybrids of sorghum is discussed.
The need to accelerate breeding for increased yield potential and better adaptation to drought and other abiotic stresses is an issue of increasing urgency. As the population continues to grow rapidly, the pressure on resources (mainly untouched land and water) is also increasing, and potential climate change poses further challenges. We discuss ways to improve the efficiency of crop breeding through a better physiological understanding by both conventional and molecular methods. Thus the review highlights the physiological basis of crop yield and its response to stresses, with special emphasis on drought. This is not just because physiology forms the basis of proper phenotyping, one of the pillars of breeding, but because a full understanding of physiology is also needed, for example, to design the traits targeted by molecular breeding approaches such as marker-assisted selection (MAS) or plant transformation or the way these traits are evaluated. Most of the information in this review deals with cereals, since they include the world's main crops, however, examples from other crops are also included. Topics covered by the review include the conceptual framework for identifying secondary traits associated with yield potential and stress adaptation, and how to measure these secondary traits in practice. The second part of the review deals with the real role of molecular breeding for complex traits from a physiological perspective. This part examines current developments in MAS and quantitative trait loci (QTL) detection as well as plant transformation. Emphasis is placed on the current limitations of these molecular approaches to improving stress adaptation and yield potential. The essay ends by presenting some ideas regarding future avenues for crop breeding given the current and possible future challenges, and on a multidisciplinary approach where physiological knowledge and proper phenotyping play a major role.
In the United States, much grain sorghum [Sorghum bicolor (L.) Moench] production area has shifted to maize (Zea maps L.) during the last 25 yr, which has been partially due to grain yield differences between these crops. The objective of this study was to document the rate of grain yield increases for maize and sorghum hybrids from 1950 to 1999 in rainfed and irrigated environments in eastern Nebraska. Across all production environments and years, maize produced 1.7 to 4.3 Mg ha(-1) greater yield than sorghum. The rate of yield increase was approximately three times faster for maize than sorghum but varied with production environments. The highest rate of yield increase (0.050 Mg ha(-1) yrl) was found for rainfed, high water-holding capacity soil conditions; the second highest rate of increase was for irrigated maize (0.028 Mg ha(-1) yr(-1)). The rate of sorghum yield increase under all environments and maize under rainfed, low water-holding capacity soil conditions was low at 0.010 to 0.015 Mg ha(-1) yr(-1): Pearson correlations indicated that the number of ears (panicles) per square meter had the highest association with yield (r = 0.68 for maize and r = 0.59 for sorghum) while both the number of kernels per ear (per panicle) and kernel weight were significantly correlated to yield for both crops. Yield component analysis for maize shows that yield increases with introduction year resulted from increased number of ears per square meter and kernel weight, while sorghum saw no significant correlation between yield and yield components.
Historical datasets have much to offer. We analyse data from winter wheat, spring and winter barley, oil seed rape, sugar beet and forage maize from the UK National List and Recommended List trials over the period 1948-2007. We find that since 1982, for the cereal crops and oil seed rape, at least 88% of the improvement in yield is attributable to genetic improvement, with little evidence that changes in agronomy have improved yields. In contrast, in the same time period, plant breeding and changes in agronomy have contributed almost equally to increased yields of forage maize and sugar beet. For the cereals prior to 1982, contributions from plant breeding were 42, 60 and 86% for winter barley, winter wheat and spring barley, respectively. These results demonstrate the overwhelming importance of plant breeding in increasing crop productivity in the UK. Winter wheat data are analysed in more detail to exemplify the use of historical data series to study and detect disease resistance breakdown, sensitivity of varieties to climatic factors, and also to test methods of genomic selection. We show that breakdown of disease resistance can cause biased estimates of variety and year effects, but that comparison of results between fungicide treated and untreated trials over years may be a means to screen for durable resistance. We find the greatest sensitivities of the winter wheat germplasm to seasonal differences in rainfall and temperature are to summer rainfall and winter temperature. Finally, for genomic selection, correlations between observed and predicted yield ranged from 0.17 to 0.83. The high correlation resulted from markers predicting kinship amongst lines rather than tagging multiple QTL. We believe the full value of these data will come from exploiting links with other experiments and experimental populations. However, not to exploit such valuable historical datasets is wasteful.
Genotype x environment (GxE) interactions due to variation in soil moisture and rainfall complicate the interpretation of sorghum hybrid performance trials over locations (L) and years (Y). This paper aims to use pattern analysis to explain measures of the GxL interaction for yield, and whether these can, in turn, be explained using simulation models to determine the occurrence of environment types (within-season patterns of drought). The aim of this work is to simplify the analysis of GxE by explaining it in terms of interactions of genotypes with environment types (ET) that are not 'fixed' to locations and years. In a sequential analysis of 17 seasons, 18 locations were separated into groups that tended to represent either the northern (i.e. central Queensland, CQ) or southern Queensland (SQ) regions. For a subset of 6 locations, ordination partially explained differences among locations as being related to latitude (r = 0.88) and rainfall (r = -0.46), but they were better related (r > 0.9) to the frequencies of 3 stress ETs as determined by long-term crop simulations. These 3 environment types were: (1) low stress (occurring in 33% of seasons); (2) severe terminal stress with an early-season (9%) or midseason time (29%) of onset; and (3) intermediate terminal stress with a midseason (9%) or late-season (20%) time of onset. Low stress ETs were more common in two SQ locations than in CQ. Stress ETs as defined by simulation models and pattern analysis had more consistent relationships with simulated yields than did the fixed descriptors of locations and years. Sorghum hybrid trials for broad adaptation in Queensland should include locations at least from each of the 2 regions and the results should be interpreted in the context of the season in which they are conducted. To match the long-term patterns in the 6 locations of the analysis, trial yields would need to sample from at least 3 yield ranges: <1 t/ha, 1-3.5 t/ha, and >3.5 t/ha. Additional seasons of testing are likely to be required when the locations used during a season do not adequately represent the target population of environments over all locations and years.
In recent years, many sorghum producers in the more marginal (<600mm annual rainfall) cropping areas of Queensland and northern New South Wales have used skip row configurations in an attempt to improve yield reliability and reduce sorghum production risk. This paper describes modi. cations made to the APSIM sorghum module to account for the difference in water usage and light interception between alternative crop planting configurations, and then demonstrates how this new model can be used to quantify the long-term benefits of skip sorghum production. Detailed measurements of light interception and water extraction from sorghum crops grown in solid, single and double skip row configurations were collected from on-farm experiments in southern Qld and northern NSW. These measurements underpinned changes to the APSIM-Sorghum model so that it accounted for the elliptical water uptake pattern below the crop row and the reduced total light interception associated with skip row configurations. Long-term simulation runs using long-term weather files for locations near the experimental sites were used to determine the value of skip row sorghum production as a means of maintaining yield reliability. These simulations showed a trade-off between long-term average production (profitability) and annual yield reliability ( risk of failure this year). Over the long term, the production of sorghum in a solid configuration produced a higher average yield compared with sorghum produced in a skip configuration. This difference in average yield is a result of the solid configuration having a higher yield potential compared with the skip configurations. Skip configurations limit the yield potential as a safeguard against crop failure. To achieve the higher average yield in the solid configuration the producer suffers some total failures. Skip configurations reduce the chance of total failure by capping the yield potential, which in turn reduces the long-term average yield. The decision on what row configuration to use should be made tactically and requires consideration of the starting soil water, the soil's plant-available water capacity (PAWC), and the farm family's current attitude to risk.
Retention of green leaf area at maturity (GLAM), known as stay-green, is used as an indicator of postanthesis drought resistance in sorghum [Sorghum bicolor (L.) Moench] breeding programs in the USA and Australia. The critical issue is whether maintaining green leaves under postanthesis drought increases grain yield in stay-green compared with senescent hybrids. Field studies were undertaken in northeastern Australia on a cracking and self-mulching gay clay. Nine closely related hybrids varying in rate of leaf senescence were grown under two water-limiting regimes, post-flowering water deficit and terminal (pre- and postflowering) water deficit, and a fully irrigated control. Under terminal water deficit, grain yield tvas correlated positively with GLAM (r = 0.75**) and negatively with rate of leaf senescence (r = -0.74**). Grain yield also increased by approximate to 0.35 Mg ha(-1) for every day that onset of leaf senescence was delayed beyond 76 DAE in the water-limited treatments. Stay-green hybrids produced 47% more postanthesis biomass than their senescent counterparts (920 vs. 624 g m(-2)) under the terminal water deficit regime. No differences in grain yield were found among eight of the nine hybrids under fully irrigated conditions, suggesting that the stay-green trait did not constrain yield in the well-watered control. The results indicate that sorghum hybrids possessing the stay-green trait have a significant yield advantage under postanthesis drought compared with hybrids not possessing this trait.
The chapter discusses the meaning and value of the biological yield and harvest index of cereals in agronomic studies and in cereal breeding. The relationship of biological yield, grain yield, and harvest index to each other and to other plant characteristics is discussed. Various models and actual relationships between biological yields and grain yields within a series of genotypes or agronomic treatments are described. The situation in which a number of varieties have precisely the same biological yield but different grain yields is graphically presented along with the genotypes that are ranked in order of increasing grain yield. Grain yield is proportional to harvest index and their correlation is 1.00, whereas biological yield and harvest index are unrelated. The chapter examines the interaction of biological yield, grain yield, and harvest index with plant density. Biological yield and harvest index are two valuable criteria for the assessment of the performance of cereals.
Current models of sorghum crop growth predict grain number using a calculated plant growth rate around flowering and a genotype-dependent parameter that describes the relationship between both traits. Few values for this parameter have been reported, being similar within triple-dwarf or single-dwarf sorghum genotypes. This approach narrows genotypic differences in grain number determination mostly to differences in traits affecting biomass production. Relevant traits such as biomass partitioning to reproductive structures and grain-set efficiency are not specifically considered, but both vary across genotypes and could improve grain number estimations. We first explored variation for these traits (CGR, crop growth rate around flowering; P-R, biomass partitioning to reproductive structures during this period; E-G, grain set per unit of accumulated reproductive biomass) for a set a sorghum commercial hybrids and inbred lines growing under different conditions. Later, we used a second set of experiments to test whether considering genotype-specific P-R and E-G improved estimates of grain number compared with the current approach used in crop simulation models. Grain number variations (14-63 x 10(3) grains m(-2)) due to genotype and environment were a consequence of significant differences (P < 0.05) in all analysed traits (CGR, P-R, E-G). Biomass partitioning and grain set per unit of accumulated reproductive biomass showed consistent genotypic differences (P < 0.001); however, they also showed significant environment or genotype x environment effects. When these specific genotypic parameters dealing with biomass partitioning and grain-set efficiency were used for estimating grain number in other non-related experiments, the predicted accuracy improved (r(2) = 0.47, P < 0.05, RMSE = 7029 grains m(-2)) relative to the general approach using a constant parameter for most genotypes (r(2) = 0.14, P < 0.28, RMSE = 12 630 grains m(-2)) or a calculated parameter for each genotype (r(2) = 0.38, P < 0.10, RMSE = 8919 grains m(-2)). We propose that these traits (P-R and E-G) need to be considered and included in sorghum crop growth models, as they help predict grain number performance of different genotypes in different growth environments.
Climatic variability in dryland production environments (E) generates variable yield and crop production risks. Optimal combinations of genotype (G) and management (M) depend strongly on E and thus vary among sites and seasons. Traditional crop improvement seeks broadly adapted genotypes to give best average performance under a standard management regime across the entire production region, with some subsequent manipulation of management regionally in response to average local environmental conditions. This process does not search the full spectrum of potential G × M × E combinations forming the adaptation landscape. Here we examine the potential value (relative to the conventional, broad adaptation approach) of exploiting specific adaptation arising from G × M × E. We present an in-silico analysis for sorghum production in Australia using the APSIM sorghum model. Crop design (G × M) is optimised for subsets of locations within the production region (specific adaptation) and is compared with the optimum G across all environments with locally modified M (broad adaptation). We find that geographic subregions that have frequencies of major environment types substantially different from that for the entire production region show greatest advantage for specific adaptation. Although the specific adaptation approach confers yield and production risk advantages at industry scale, even greater benefits should be achievable with better predictors of environment-type likelihood than that conferred by location alone.
In Argentina, peanut (Arachis hypogaea L.) breeding has been based on seed yield per se plus defensive and seed quality traits. An important milestone was the shift from cultivars with erect growth habit (CEGH) to cultivars with procumbent (CPGH) growth habit that took place in the 1970s. However, there is no information on the genetic gain obtained for seed yield and related secondary traits (numerical and physiological determinants of seed yield), or on the effect of growth habit shift on these traits. Field experiments were performed to compute this gain and the relationships between traits in potential growing conditions. Eight cultivars released between 1948 and 2004 were evaluated. Introduction of the procumbent habit in 1975 produced a mean increase of 52% in seed yield, which was related to year of cultivar release (YOR) only for CPGH (mean genetic gain of 0.43% y−1). This trend was driven by seed weight, a trait that registered a mean genetic gain of 0.29% y−1 (P = 0.026) only among procumbent cultivars (56% increase with habit change between 1973 and 1975). No genetic gain was computed for seed numbers, and only a 10% difference was registered between growth habits (CPGH > CEGH). Seed number was related to crop growth rate between R3 and R6.5 (r2 = 0.55, P < 0.001). This rate was higher for CPGH than for CEGH. Breeding increased the number of flowers per plant (0.86% y−1), and the number of pods per plant and pod set (CPGH > CEGH). Breeding had a clear effect (P < 0.001) on the determinants of seed weight, and a genetic gain of 0.52% y−1 was estimated for pod growth rate. Introduction of CPGH enhanced pod growth duration (37% increase). No trade-off was detected between seed number and seed weight because there was no source limitation to seed filling. Therefore, peanut seed yield might be further increased by improving the determinants of seed numbers and seed weight simultaneously.
There is evidence that soybean yield needs to increase at faster rates to satisfy a growing demand. Because yield is mostly determined by the number of harvested seeds, we used a seed number determination framework for phenotyping a large set of cultivars. This framework incorporates biomass accumulation during the seed set period, biomass partitioning to reproductive structures and seed set efficiency per unit of accumulated reproductive biomass. Our objectives were: (i) identify clusters of cultivars differing in seed number across environments, (ii) describe average differences among clusters for the parameters that determine seed number, (iii) evaluate parameter variation within the highest yielding clusters. Objectives were independently tested at central USA and central Argentina (ARG) using cultivars from each region (61 at USA and 25 at ARG). Clusters differing in seed number across environments were identified. Seed number was associated with rapid growth rates (USA only), increased partitioning and greater seed set efficiency. In spite of these differences between clusters, there was significant residual variation among genotypes within highest yielding clusters for most physiological parameters. Our study provided evidence there is no unique physiological pathway for achieving high yields in either environment. This indicated developing targeted segregating populations using high yielding parents with contrasting physiological strategies is feasible. It provides an opportunity for testing yield increases using ideotype construction by pyramiding desirable physiological parameters.
Understanding the intrapanicle pattern of caryopsis weights commonly found in sorghum [ Sorghum bicolor (L.) Moench] fields and the factors that result in changes in this pattern would help in determining limitations on caryopsis weight. Our objectives were to determine the pattern of caryopsis weights found in the sorghum panicle, the effect of assimilate supply on the weight pattern, and whether this pattern resulted from the rate of grain fill or length of the effective fill period (EPP). Two dryland field studies were conducted at Manhattan, KS, in 1989 and 1990 on a Reading silt loam (fine‐silty, mixed, mesic Typic Argiudoll; 0–1% slope). In 1989, panicles of DeKalb ‘DK 46’ and Pioneer ‘8500’ tagged at anthesis were harvested at regular intervals. In 1990, seven population‐light treatments were applied to Pioneer 8500 either at anthesis or 7 d after anthesis. Panicles from both experiments were separated into four sections. Caryopses from these sections were used to determine differences in caryopsis weights, rate of grain fill, and length of the EPP. In 1989, caryopsis weights within the sorghum panicle increased from 20.2 mg caryopsis ⁻¹ at the base to 22.8 mg caryopsis ⁻¹ at the apex. In 1990, this same intrapanicle pattern was observed in all treatments that had medium or high plant populations during the EPP. This pattern was caused by increases in the rate of grain fill from the base to apex of the panicle. In the low population treatments in 1990, caryopses in the middle of the panicle were as heavy or heavier than those in the apex. This was the result of intrapanicle grain‐fill rates that were more uniform and an increase in the length of the EPP from the apex to the base of the panicle.
‘Georgia 615’ grain sorghum ( Sorghum bicolor (L.) Moench) was shaded for weekly periods in three field experiments to determine if periods exist during the life cycle of the sorghum plant when low light intensities are deleterious to grain yield components. Black plastic fabric with 25% light transmission was used to shade plants. Grain yield per ha and per panicle, seed number per panicle, seed weight, and heat units from seeding to 50% anthesis were determined.
Two stages of plant development most adversely affected by low light intensity were found. The first stage occurred from pre‐boot vegetative, when the last leaf was just visible in the whorl to full panicle expansion or during approximately the two‐week period just before 50% anthesis. Shading during this period resulted in reduced number of seed per panicle. The second stage was during the milk and dough stages of grain development or during approximately the three‐week period just after 50% anthesis. Shading during this period resulted in lighter sed with little or no change in number of seed per panicle. When number of seed per panicle was reduced by shading, heavier seed weight compensated for part, and sometimes all, of the potential yield decrease. Grain yields per panicle and per ha of shaded sorghum were generally lower than for the unshaded check.
Sorghum [Sorghum bicolor (L.) Moench] grain yield has improved since the deployment of hybrid sorghum in the mid-1950s. However, information on the contribution of different factors to this yield increase for irrigated and dryland sorghum production is scarce. The objective of the present study was to determine the magnitude of change in irrigated and dryland sorghum yields with hybrid improvement and changes in agronomic practices. Data from selected irrigated and dryland grain sorghum performance trials conducted in Kansas from 1957 to 2008 were analyzed. The mean yield of the highest-yielding hybrid over years was 9.3 Mg ha(-1) at irrigated sites and 5.8 Mg ha(-1) at the dryland sites. There was an increase in hybrid yield of nearly 50 kg ha(-1) yr(-1) in dryland sites over the 52 yr analyzed. Irrigated grain sorghum yields, however, remained unchanged over the same period. Agronomic practices such as planting date, P fertilizer use, and planting density changed over these years but were not found to contribute to increased dryland sorghum yields. Hybrid advancement and increased N fertilizer application were responsible for changes in dryland yields. The yield focus of sorghum hybrid development was effective in dryland sorghum production, likely because of intentional or inadvertent selection of hybrids with better drought tolerance.
Leaf area dynamics are controlled by genotypic and environmental influences. In this series of papers, general models of leaf area dynamics of uniculm and tillering sorghum (Sorghum bicolor (L.) Moench) at the whole plant and individual leaf levels were developed to examine and quantify both genotypic and environmental controls. Green leaf area was modelled by examining leaf area production and senescence separately. Data from field experiments involving broad ranges of hybrids and environments were collated and analysed. Crops were grown with adequate water and nutrient supply.In this paper, a general framework to model leaf area production at the whole plant level is presented. Accumulation of total plant leaf area (TPLA) (without losses due to senescence) was simulated using a logistic function of thermal time (TT) from emergence and it increased to its maximum value (TPLAmax) shortly before flowering. To calculate TT, base optimum and maximum temperatures of 11, 30 and 42° C respectively were derived by examining the effect of temperature on rate of appearance of fully expanded leaves. Hence, TT incorporated the major effect exerted on TPLA by temperature. Most remaining genotypic and environmental variation in TPLA was related to variation in TPLAmax. Values of TPLAmax were predicted from total leaf number on the main culm (TLN) and fertile tiller number per plant (FTN) by allowing for a curvilinear increase in TPLAmax with TLN and a sequential decrease in total leaf area produced by successive surviving tillers relative to that on the main culm. The potential genotypic and environmental controls on TPLA, introduced via factors affecting TLN and FTN, were considered. Frr seven hybrids grown in eight environments (locations and times of planting), this simple general model accounted for 93% of observed variation in TPLA with time, with a root mean square deviation of 664 cm2 for observed values of TPLA ranging from 161 to 11 302 cm2.
Research with grain sorghum often involves sampling several times during the growth cycle. Samplings often are designated by calendar date, days after planting or emergence, or plant height. Often these bear little or no actual relationship to the morphological or physiological age or status of the plant.Although certain stages of sorghum growth are fairly well established, the growth cycle of sorghum has not been fully described. Therefore, a standard set of growth stages needs to be defined. Based on detailed studies of grain sorghum hybrids of different maturities, the following ten stages of development have been defined and illustrated: emergence, three-leaf, five-leaf, growing-point, differentiation, final leaf visible in whorl, boot, half-bloom, soft dough, hard dough, and physiological maturity. These stages are suggested as standards to describe the timing of sampling or treating sorghum.
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Knowledge of changes associated with advances in crop productivity is essential for understanding yield-limiting factors and developing strategies for future improvement. Our objective was to identify plant traits associated with gains in grain yield of winter wheat (Triticum aestivum L.) in the Great Plains. Twelve landmark cultivars and one experimental line were compared with 'Turkey' (introduced 1873) at Hutchinson (Clark-Ost complex soil) and Manhattan (Reading silt loam soil), KS, during 1996-1997 and 1998-1999. Agronomic traits, leaf rust infection (caused by Puccinia recondita Rob. ex Desm. f. sp. tritici), and grain yield and its components were measured. Grain yields ranged from 2718 kg ha -1 for Turkey to 4987 kg ha -1 for the experimental line, with mean genetic gains of 0.16% per year for early genotypes and 0.63% per year for recent genotypes. Kernel number per unit of soil area had the highest phenotypic correlation with grain yield and contributed most to its genetic gain. Gains in spike numbers per unit of soil area and above-ground biomass also contributed significantly to higher yields of some genotypes. Significant genetic changes over time and correlations with grain yield were observed for early heading, decreased height, and reduced lodging and leaf rust but not for kernel weight. Our results suggested that yield components that form during vegetative phases (spike numbers per unit of soil area and kernels per spike) when conditions for growth are generally favorable are more amenable to genetic improvement than kernel weight, which forms during maturation when moisture and temperature are often unfavorable.
Changes in post-anthesis physiological attributes related to genetic improvement for grain-yield were studied for six Chinese maize (Zea mays L.) hybrids widely grown in North China during the past 50 years. The characteristics assessed included light-saturated photosynthetic rate (Psat), chlorophyll content, soluble protein content, maximal efficiency of PS2 photochemistry (Fv/Fm), PS2 efficiency (ΦPS2), ribulose-1,5-bisphosphate carboxylase (RuBPCase) activity and phosphoenolpyruvate carboxylase (PEPCase) activity. We found that Psat of the newer hybrids was not always higher than the older ones. However, Psat of the 1950s hybrids was the highest among all at flowering stage, which was associated with their high PEPCase activity and soluble protein content. Post-anthesis changes in Psat of the older hybrids can be divided into two phases. During the first phase, which was the decisive phase of grain filling, Psat of the older hybrids declined gradually whereas the new hybrids remained relatively constant. Psat of 1950s hybrids was not the highest among all maize hybrids any longer although their PEPCase activities were also the highest. The reduction in Psat of the older hybrids during this phase was associated with a reduction in the chlorophyll content and the soluble protein content but was not influenced by the specific activity of RuBPCase and PEPCase. Adapting to the lowered CO2 assimilation capacity, a down-regulation of ΦPS2 occurred in the older hybrids to protect the photosynthetic apparatus from photo-damage by strong light, while Fv/Fm only decreased slightly during this phase, suggesting a functional PS2 apparatus in senescent flag leaves. During the second phase, the older hybrids underwent an irreversible leaf senescence that certain photosynthetic traits declined substantially with Psat, whereas the photosynthetic components of the newer hybrids remained functional. Newer maize hybrids produced higher grain yield compared to the old ones mainly because they could remain photosynthetically active when the older hybrids aged during the grain-filling period. The decline in photosynthetic rate of older hybrids during senescence is generally attributed to the degradation of both structural and functional components of chloroplasts.
To quantify the genetic gain in yield and associated changes in phenotype, we compared 13 South Australian wheat varieties released between 1958 and 2007. Crops were grown in three environments with a range of yield between 4.1 and 6.1 t/ha. Yield increased linearly with year of cultivar release at a rate of 25 ± 3.4 kg/ha per year. Yield improvement was associated with a linear increase in harvest index over the whole period 1958–2007 and increased shoot biomass for varieties released after the early 1980s. A non-linear model with an inflection point at 1982 ± 1.6 emphasised two phases in the time trend of grain size: it decreased between 1957 and 1982 and increased afterwards. The plasticity of grain size increased 2-fold after 1982. Grain number increased until the early 1980s and stabilised afterwards.
Post-flowering drought tolerance is referred to as the stay green trait in sorghum. Plants with stay green resist drought-induced premature plant senescence. In breeding programmes, stay green is evaluated under limited irrigation, post-flowering moisture-stress field conditions and visually scored at or soon after physiological grain maturity. The objective of this study was to investigate the relationship between the stay green rating and total leaf chlorophyll content. The parents B35 and Tx7000, and their 98 F, recombinant inbred lines were evaluated in replicated field trials under limited (post-flowering stress) and full-irrigation (non-stress) conditions. After scoring the stay green trait of stressed plants, total leaf chlorophyll contents were measured with a chlorophyll meter (SPAD values) and a spectrophotometer method. The SPAD value had a significant linear relationship with total leaf chlorophyll (R2= 0.91) and with visual stay green rating (with R2= 0.82). Relative water content in top leaves of the stay green lines was about 81%, much higher than non-stay green lines (38%), indicating that the stay green lines kept the stalk transporting system functioning under severe drought conditions, The results indicate that visual stay green ratings were a reliable indicator of leaf senescence an should be useful to sorghum breeders in evaluating progeny when breeding for drought tolerance.
A simple method of analysis was proposed to characterize the impact of climatic conditions of a wide region of Argentina (from
27°05′S to 35°48′S, from 61°5′W to 64°21′W) on potential maize (Zea mays L.) grain yield, and the occurrence of various climatic constraints (low temperatures and low soil water content, frost,
drought stress and heat stress) along the cycle. The analysis was based on previous studies of the eco-physiology of maize
crops and the use of climatic records of six locations in the region under study. Results were analyzed using a probabilistic
method, later organized as a checklist to consider when deciding on sowing date in a location of the region. Thus, for each
production scenario (combination of location and sowing date), farmers would have a tool enabling them to pay particular attention
to the restrictions more likely to occur, to include some cultural practices to avoid or mitigate the most severe climatic
constraint to maize production.
Understanding source or sink limitations on crop yield is critical for the rational design of agricultural practices as well as breeding strategies. In the present article, we studied sorghum [Sorghum bicolor (L.) Moench] source–sink yield limitations during grain filling, and tested the hypothesis that the time in which kernel maximum water content is reached during grain filling defines a temporal limit for the crop to profit from source increases. Earlier studies have never tested increasing assimilate availability per kernel in different developmental stages. We conducted a field experiment increasing assimilate availability per kernel at anthesis and 15 days after anthesis in commercial hybrids. The anthesis treatment was aimed to increase assimilates per kernel from early grain filling, and the 15 days after anthesis treatment from the stage kernel maximum water content was achieved. Both treatments removed 50% of the kernels from one side of the panicle. Kernel dry weight (KW), kernel water content and kernel volume were measured in apical and basal positions of the panicle throughout grain filling. Increased assimilate availability always yielded a higher KW (∼34% increase). This KW increase was consistent across the two kernel developmental stages when the treatment was imposed, the panicle position and hybrid. Achieving maximum water content did not prevent kernels from increasing their weight when assimilates were subsequently increased. Final KW was closely related to maximum kernel volume (r2 = 0.72; n = 42; p < 0.0001). Increased assimilate availability per kernel promoted changes in both kernel growth rate and duration of grain filling.
Genetic and agronomic contributions to yield gains for wheat (Triticum aestivum L.) in the Yaqui Valley of northwest Mexico were estimated for the period from 1968–1990. Five problems associated with estimating sources of yield gains were considered, namely: (1) adjusting yield gains for variation in weather over the study period; (2) considering annual cultivar-by-weather interactions, which are potentially problematic when relative yields of cultivars are generated over only part of the study period; (3) overestimating relative yields of cultivars if the check cultivar(s) become susceptible to disease; (4) ensuring that yields as estimated from research station trials represent cultivar performance under farmers' conditions; and (5) allowing for cultivar-by-management interactions. With these factors considered, 28% of the weather-adjusted yield gain of 103 kg ha−1 y−1 was attributed to genetic gain (i.e., cultivar improvement). If the yield gains had not been adjusted for annual weather variation, genetic gain would have been overestimated at 50%. By contrast, 48% of the gain was attributed to increased use of N fertilizer, driven at least in part by a decline in N prices; no N-by-cultivar interactions were apparent. The remainder of the yield gap (24%) could not be attributed to specific factors, although P application rates increased over time, and negative deviations from linearity were associated with years having greater than normal rainfall in November and December (a phenomenon which can delay sowing and/or reduce crop stand). In addition to identifying factors contributing to yield gains, technologies that have contributed benefits not measured by yield are discussed.
Genetic gains in grain yield and related phenotypic attributes have been extensively documented in maize (Zea mays L.), but the effect of breeding on the physiological determinants of grain yield is yet poorly understood. We determined genetic gains in grain yield and related physiological traits for seven maize hybrids developed for the central region of Argentina between 1965 and 1997. Gains were expressed as a function of the year of release (YOR). Hybrids were cropped in the field at five stand densities (from almost isolated plants to supra-optimal levels) during two contrasting growing seasons (E1 and E2). Water and nutrient stress were prevented and pests controlled. Genetic gains in grain yield (≥13.2 g m−2 YOR−1) were mainly associated with improved kernel number, enhanced postsilking biomass production, and enhanced biomass allocation to reproductive sinks, but computed gains were affected by the environment. Differences among hybrids arose at the start of the critical period, and were evident as improved mean radiation use efficiency (≥0.026 g MJ−1 YOR−1), enhanced plant growth rate at near optimum stand density (≥0.04 g pl−1 YOR−1), and improved biomass partitioning to the ear around silking (0.0034 YOR−1, only for E1). Improved biomass production after silking was related to an increased light interception (≥4.7 MJ m−2 YOR−1), and allowed for an almost constant source–sink ratio during grain filling. This trend determined no trade-off between kernel number and kernel weight. In contrast to previous studies, genetic gains were detected for potential productivity (e.g., maximum grain yield) on a per plant basis (i.e., under no resource competition), a promising aspect for the improvement of crop grain yield potential.
A procedure for forming hierarchical groups of mutually exclusive subsets, each of which has members that are maximally similar with respect to specified characteristics, is suggested for use in large-scale (n > 100) studies when a precise optimal solution for a specified number of groups is not practical. Given n sets, this procedure permits their reduction to n − 1 mutually exclusive sets by considering the union of all possible n(n − 1)/2 pairs and selecting a union having a maximal value for the functional relation, or objective function, that reflects the criterion chosen by the investigator. By repeating this process until only one group remains, the complete hierarchical structure and a quantitative estimate of the loss associated with each stage in the grouping can be obtained. A general flowchart helpful in computer programming and a numerical example are included.
Grain number is an important component of grain yield in sorghum. Research in wheat and maize has indicated a dependency of grain number on the crop or panicle growth rate around anthesis (CGRa and PGRa respectively), but little quantitative information is available for sorghum. The aim of this paper was firstly to quantify the effect of CGRa and PGRa on grain number and secondly, to identify other parameters that could be used as substitutes for PGRa. Analyses included data from a number of experiments, covering a range in nitrogen and drought treatments and including both tall (single dwarf) and short (triple dwarf) hybrids. CGRa and SGRa (stem growth rate) were calculated from the derivative of a curvilinear function fitted to experimental data, and PGRa was obtained by subtraction of SGRa from CGRa. Results indicated a linear relationship between grain number and CGRa, but the slope differed for tall and short hybrids. This was due to a difference in the proportion of dry matter allocated to the reproductive organs around anthesis (Pr), as PGRa was closely related to grain number, irrespective of crop height. Since panicle dry mass at maturity (excluding grain) was closely correlated with reproductive biomass shortly after anthesis, this indicator represents an integration of panicle growth during the critical period for yield determination in sorghum (i.e. flag leaf until start of grain filling). Panicle biomass at maturity (excluding grain) was thus also linearly related to grain number, and the relationship was independent of crop height and of the timing, severity, or type of stress. Our results indicate that panicle mass at maturity could provide an alternative to PGRa for the estimation of grain number.
This paper applies linear mixed model and pattern analyses to 122 on-farm trials of commercial and near-commercial sunflower (Helianthus annuus L.) hybrids grown over 15 years in 32 locations of central Argentina to determine the contributions of change in characteristics of germplasm pools to increases in oil yield. The 'Relative Peak Performance' (best linear unbiased predictors, BLUPs) of 49 hybrids released for the conventional market between 1983 and 2005 showed genetic gains of 11.9 kg ha(-1) year 1, 0. 19% year(-1) and 16.1 kg ha(-1) year(-1) for oil yield, grain-oil concentration and grain yield, respectively. Oil yield improvement was consistent across three market segments and a biplot of genotype-by-attribute BLUPs summarised 20 years of breeding to demonstrate how the merging of two germplasm pools of differing maturity, achene type and grain-oil concentration resulted in step-wise improvements in grain yield and grain-oil concentration and a move toward an intermediate maturity. The analysis of general combining ability within a breeding program shows that the female and male germplasm pools were improved in different ways over time. On the female side, much of this improvement was to encompass different combinations of the determining traits of oil yield, while on the male side the improvement was more linear in terms of exploitation of genotypic variance for oil yield per se. (c) 2006 Elsevier B.V. All rights reserved.
This paper applies linear mixed model analysis to 122 on-farm trials of commercial and near-commercial sunflower (Helianthus annuus L.) hybrids grown over 15 years in 32 locations of central Argentina to quantify increases in oil yield and to determine the contributions of change in both biotic stress resistance and yielding ability in favourable environments. The best linear unbiased predictors (BLUPs) from this analysis can be regarded as measures of 'relative peak performance' of hybrids in environments for which they were selected, and are a better measure of their adaptation compared to small trial sets of 'historical' hybrids. The BLUPs of 49 commercial hybrids released between 1983 and 2005 showed a genetic gain for oil yield of 11.9 kg ha(-1) yr(-1). Special purpose hybrids that were converted for single traits or that were developed for low-technology markets lagged by 5-15 years in terms of genetic gain. Genetic gains came about due to both an increase in the number of hybrids with resistance to the major biotic stress (Verticillium dahliae Klebahn) and a genetic gain in oil yield of 14.4 kg ha(-1) yr(-1) within these hybrids. Based on the data and the estimated time lag between commercial release and peak use, the improvement in oil and grain yield of conventional hybrids in central Argentina will be sustained until at least 2010, with evidence that the new germplasm pools still have substantial genetic variance to be exploited. (c) 2006 Elsevier B.V. All rights reserved.
Sorghum (Sorghum bicolor (L.) Moench) and cotton (Gossypium hirsutum L.) are the summer crops traditionally grown in the rainfed or supplementary irrigated areas of the semi-arid southern Great Plains. Both crops have the ability to withstand periods of water deficit and to yield an economic return to the farmer.Numerous traits contribute to drought tolerance in both sorghum and cotton. Only limited breeding effort has been expended on identifying or combining such traits. Drought tolerance has seldom been a primary breeding objective, usually addressed indirectly under major objectives such as improved yield, pest resistance, and adaptation.In sorghum, recent emphasis on field screening under severe drought stress has led to significant developments in the understanding of drought tolerance. Two distinct types of stress responses have been identified. One type is expressed when plants are stressed prior to flowering, while the other is expressed when stress occurs during grain fill. Excellent sources of tolerance to each type of stress have been identified, but high levels of both types of tolerance have not been found in the same genotype. Crosses among contrasting types of tolerance are being evaluated.In cotton, emphasis has been placed on screening primitive photoperiodic-sensitive strains from the world collection. Primary effort has been expended on identifying parental strains that have unique responses to water stress and determining why these responses occur. Physiological evaluations are used extensively to define potentially useful traits. These traits are then incorporated into agronomically desirable germplasm. Germplasm lines chosen through this approach yielded more than commercial varieties under water deficient conditions in preliminary evaluations.Field screening at more than one location with different water regimes can be used to insure stress at different stages of growth. Rainout shelters and irrigation gradient systems can be used to supplement field screening.