-
Functional Plant Biology 01/2010; 37:166. · 2.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Many candidate physiological traits have been suggested for wheat improvement under moisture stress and genetic diversity
is present in the wheat gene pool for most of them. The objective of this study was to quantify the probable yield effect
associated with variation in the expression of such traits within two sets of germplasm;Sisters(from an elite x elite cross) showing a range of drought adaptation, andDiverselines (representing synthetic-derived wheat as well as selected landraces) assembled for favourable expression of one or more
of the following traits under moisture stress: final biomass, ability to extract water at depth from the soil, remobilization
of stem soluble carbohydrates, and transpiration & water-use efficiency (WUE). Agronomic and physiological traits were measured
in NW Mexico in 2005 under post-anthesis moisture stress that resulted in yield reductions of up to 65% compared with irrigated
plots, depending on the genotype. There was a significant range of expression for all traits measured and calculations were
performed to gain an idea of the relative potential contribution to crop performance if trait expression were maximized in
the highest-yielding backgrounds. Theoretically, remobilization of stem carbohydrates would be associated with 7% yield gains
forSisterand 20% forDiverse Lines. Maximizing WUE could achieve 16% and 4% gains in yield inSisterandDiverse Linesrespectively, despite the already strong association of the trait with yield, and similar results were found for transpiration
efficiency. In both sets of germplasm, putting the best expression for water extraction (to 120cm) in the highest yielding
background was associated with yield gains of 13%. Taken together these results suggest substantial yield gains under moisture
stress are achievable if the genes representing these traits were to be combined using a complementary-trait based approach
to breeding
05/2007: pages 331-340;
-
[show abstract]
[hide abstract]
ABSTRACT: In plant physiology and breeding, it is important to understand the causes of genotype×environment interactions (GEIs) of complex traits such as grain yield. It is difficult to study the underlying sequential biological processes of such traits, their components and other intermediate traits, as well as the main environmental factors affecting those processes. The structural equation models (SEMs) used in the present study allow the external and internal factors affecting GEI of various traits and their interrelations to be accounted for. The study included 86 wheat genotypes derived from three different crosses and evaluated over 3 years. Several attributes, as well as grain yield and yield components, were measured during five crop development stages. Environmental data for the five development stages were averaged. The SEM approach facilitated comprehensive understanding of GEI effects among the different traits, and decomposed the total effects of grain yield components and cross-product covariates on grain yield GEI into direct and indirect effects. External climatic variables were related mostly to main final yield components, and only more intermediate endogenous variables, such as spikes/m2, were affected by minimum temperature and radiation in the early stages of plant development.
The Journal of Agricultural Science 03/2007; 145(02):151 - 161. · 2.04 Impact Factor
-
Crop Sci. 01/2007; 47:172.
-
[show abstract]
[hide abstract]
ABSTRACT: The physiological-trait-based breeding approach has merit over breeding for yield per se because it increases the probability of crosses resulting in additive gene action. While considerable investment in germplasm characterization is required, conceptual models of crop genotypes can be employed as research tools to quantify likely genetic gains associated with specific trait or in defining traits that may have generic value across different stresses. For example, deeper root growth that permits better access to soil water has obvious benefit under drought, while under hot, irrigated conditions permits leaf canopies to match the high evaporative demand associated with hot, low-relative-humidity environments, resulting in higher leaf gas-exchange rates and heat escape through evaporative cooling. Although improvement in adaptation to abiotic stress may occur as a result of transgressive segregation, exotic parents can be used to increase total allelic diversity for such traits. The bread-wheat-breeding programme at CIMMYT is exploiting new genetic diversity using inter-specific hybridization of the ancestral genomes of bread wheat. Novel genetic diversity is also being accessed more directly by crossing adapted germplasm with landrace accessions originating in abiotically stressed environments that have become isolated from mainstream gene pools. Through studying these genetic resources it has been possible to calculate the theoretical impact of combining their best values of trait expression into the check cultivar to gain some insight into which traits may hold most promise in terms of genetic enhancement. It was apparent that the genetic diversity found for water use efficiency offers the greatest and most consistent opportunity for increasing yield, while increasing stem carbohydrates and access to water at depth also shows some potential. Direct physiological interventions in breeding include (i) characterization of potential parents for more strategic crossing; (ii) early-generation selection; and (iii) evaluation of promising genetic resources in pre-breeding. The early-generation selection trait 'canopy temperature' (measured with an infrared thermometer) has been readily adopted since measurement is quick, easy and inexpensive. Although genetic markers are not currently used in selection for complex traits, as technology advances and combines with gene discovery approaches, more quantitative trait loci (QTLs) associated with adaptation to complex environments will emerge. A multi-staged approach to identifying molecular markers may be the best approach where QTLs for generic traits – i.e., valid across a range of environments – are identified in well controlled field environments and used to optimize germplasm. Subsequently, environment-specific models would be used to factor in additional traits commonly found in a specific region that may not be directly related to moisture stress, factors such as nematodes or microelement deficiency or toxicity that are exacerbated under drought.
01/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m-2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag-leaf photosynthetic rate during grain-filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post-anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain-filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag-leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi-ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.
Annals of Applied Biology 02/2005; 146(1):39 - 49. · 2.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The material in genebanks includes valuable traditional varieties andlandraces, non-domesticated species, advanced and obsolete cultivars,breeding lines and genetic stock. It is the wide variety of potentially usefulgenetic diversity that makes collections valuable. While most of the yieldincreases to date have resulted from manipulation of a few major traits(such as height, photoperiodism, and vernalization), meeting future demandfor increased yields will require exploitation of novel genetic resources.Many traits have been reported to have potential to enhance yield, andhigh expression of these can be found in germplasm collections. To boostyield in irrigated situations, spike fertility must be improved simultaneouslywith photosynthetic capacity. CIMMYT''s Wheat Genetic Resourcesprogram has identified a source of multi-ovary florets, with up to 6 kernelsper floret. Lines from landrace collections have been identified that havevery high chlorophyll concentration, which may increase leaf photosyntheticrate. High chlorophyll concentration and high stomatal conductance areassociated with heat tolerance. Recent studies, through augmented use ofseed multiplication nurseries, identified high expression of these traits inbank accessions, and both traits were heritable. Searches are underway fordrought tolerance traits related to remobilization of stem fructans, awnphotosynthesis, osmotic adjustment, and pubescence. Genetic diversityfrom wild relatives through the production of synthetic wheats hasproduced novel genetic diversity.
Euphytica 04/2001; 119(1):25-32. · 1.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The physiological and genetic basis of yield improvement in wheat isonly partially understood. Nonetheless, a significant increase in yield andbiomass has been observed in several backgrounds when alien chromatinassociated with Lr19 was introgressed from Agropyronelongatum. Theoretically, higher yield and biomass may be achievedthrough (i) greater interception of incident radiation, (ii) increasedradiation use efficiency, (iii) a more optimal source-sink balance permittinghigher sink demand and/or a higher partitioning of assimilates to yield. Theobjectives of the current study were to evaluate the performance of nearisogenic lines differing in Lr19 to observe the physiological basis ofsuperior performance. Lr19 was associated with increases in yield(average 13%), final biomass (10%) and grain number (15%) in allbackgrounds studied. Differences were not associated with improved lightinterception based on measurements of biomass shortly after canopyclosure, nor with improved radiation use efficiency (RUE) prior to grainfilling based on biomass accumulation rate and direct measurement offlag-leaf photosynthetic rate prior to anthesis. Lr19 was associatedwith an increased partitioning of biomass to spike growth at anthesis(13%), a higher grain number per spike, and higher RUE and flag-leafphotosynthetic rate during grain filling. The mechanism causing increasedpartitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilationcapacity.
Euphytica 04/2001; 119(1):139-144. · 1.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Large areas of wheat (Triticum aestivum L. Fion et Paol.) are grown under above-optimal temperatures causing significant yield reductions. Adaptation of wheat to such areas through genetic improvement is a way of increasing production in those regions. To identify new and novel sources of heat tolerance, 2,255 Mexican wheat landraces, grown for seed regeneration under semi-controlled conditions in the screenhouse, were evaluated for leaf chlorophyll content (LCC). The landraces were collected from areas with seasonal high temperatures. Based on these initial results, two subgroups of 127 landraces each were selected, one with high LCC values and one with low LCC values. During 1997 the selected subgroups were grown in the screenhouse and in field trials in Cd. Obregon, Mexico. The landraces were evaluated for traits associated with heat tolerance: LCC, canopy temperature depression, and thousand-kernel weight (KWT). The objectives of the study were to identify new sources of heat tolerance and to assess the feasibility of combining basic seed regeneration with characterization for needed traits like heat tolerance. A highly significant correlation was found between LCC in the screenhouse and in field trials, indicating the promise of using a screenhouse for cost effective evaluation of heat tolerance traits. This strategy could be used to identify regions or groups of germplasm that merit more intense screening. Highly significant correlations were also found between LCC and KWT. Three landrace cultivars with superior and consistent LCC values were identified. These accessions are potentially useful sources for improving heat tolerance in cultivated wheat.
Genetic Resources and Crop Evolution 01/1999; 46(1):37-45. · 1.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two cereal cropping systems are described which, through the introduction of a leguminous intercrop, increased productivity, nitrogen output and ground cover of the systems in the absence of added nitrogen fertilizer. Nitrogen-fixing legumes were cultivated between rows of wheat or barley grown at low levels of soil nitrogen, and mostly under rainfed conditions, in Mexico between 1989 and 1992. None of the legumes tested reduced yields of the cereal crop in comparison to controls where cereal yields were in the range of 1–4 t/ha, while the extra total biomass from legumes in some cases more than doubled productivity. Different legume crops were tested to demonstrate the adaptability of the system to the varying needs of farmers. The intercropped legumes achieved dry biomass yields as high as 6·5 t/ha in the case of a sequentially cropped forage crop of hairy vetch, or 1·4 t/ha of dry beans plus 3·5 t/ha of green residue in the case of Vicia faba. Total biomass in the intercropped situation gave land equivalent ratios as high as 1·54. Light measurements inside the crop canopies indicated that the intercropped systems intercepted a higher proportion of the incident solar radiation than the cereal monocrop, presumably accounting for the large differences in total biomass produced. In addition, with leaf nitrogen levels of 3·8%, it is assumed that the intercropped legumes fixed considerably more nitrogen than was removed by the wheat crop. The potential of the system to stabilize erodible soils by increasing ground cover as well as by raising inputs of soil organic matteris discussed.
The Journal of Agricultural Science 09/1994; 123(02):175 - 183. · 2.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Wheat cultivars often show highly significant genotype by environment interaction (G×E) for yield, even when comparing different years within a relatively stable location. This study attempts to explain some of the physiological bases of G×E in two experiments: (i) historic yield potential trials (HYPTs) of bread wheat (Triticum aestivum L.), durum (T. durum Desf.) and triticale (X Triticosecale Wittmack) cultivars grown under agronomically optimal conditions; (ii) an elite spring wheat yield trial (ESWYT) of 30 bread wheat genotypes cultivated at 27 international locations. For the HYPT, the main objectives were to determine the environmental variables during different phenological stages associated with: (i) G×E among the three crop species, (ii) G×E within each species, and (iii) underlying physiological causes of G×E. For ESWYT, meteorological data were not available and so mean site values of certain crop parameters were used as proxy environmental data to determine whether conditions either pre- or post-anthesis were more influential in determining G×E. Partial least-squares analysis and factorial regression models were used to identify the environmental factors best explaining G×E independent of the main effects. Of the three crops, durums were shown to be the most sensitive to conditions pre-anthesis, requiring higher radiation and cooler average temperatures in order to set high grain number. Triticale, despite having the highest average yield and biomass, performed relatively poor when conditions from spike growth stage onwards were sunny and warm. Bread wheat appeared to be the most robust of the three species. Considering yield, biomass, and yield components, it was apparent that the spike primordia growth stage was generally the most sensitive to environmental factors causing G×E. Results for the ESWYT suggested that conditions post-anthesis were more influential on G×E than conditions pre-anthesis. Implications for how such analysis may assist with both conventional and molecular approaches to breeding are discussed.
Field Crops Research.
-
-
[show abstract]
[hide abstract]
ABSTRACT: Received for publication August 7, 2000. Multienvironment trials are important in agronomy because the effects of agronomic treatments can change differentially in relation to environmental changes, producing a treatment x environment interaction (T x E). The aim of this study was to find a parsimonious description of the T x E existing in the 24 agronomic treatments evaluated during 10 consecutive years by (i) investigating the factorial structure of the treatments to reduce the number of treatment terms in the interaction and (ii) using quantitative year covariables to replace the qualitative variable year. Multiple factorial regression (MFR) for specific T x E terms was performed using standard forward selection procedures for finding year covariables that could replace the factor year in those T x E terms. Subsequently, we compared the results of the final MFR with those of a partial least squares based analysis to achieve extra insight in both the T x E and final MFR model. The MFR model with a stepwise procedure used in this study for describing the T x E showed that the most important interaction with year was that due to different N fertilizer levels and the most important environmental variables that explained year x N interaction were minimum temperatures in January, February, and March and maximum temperature in April. Evaporation in December and April were important covariables for describing year x tillage and year x summer crop interactions, whereas precipitation in December and sun hours in February were important for explaining the year x manure interaction. We also discuss the parallels with extended additive main effect and multiplicative interaction analysis. Biological interpretation of the results are provided.
Agronomy Journal 93 (2001).
-
[show abstract]
[hide abstract]
ABSTRACT: The material in genebanks includes valuable traditional varieties and landraces, non-domesticated species, advanced and obsolete cultivars, breeding lines and genetic stock. It is the wide variety of potentially useful genetic diversity that makes collections valuable. While most of the yield increases to date have resulted from manipulation of a few major traits (such as height, photoperiodism, and vernalization), meeting future demand for increased yields will require exploitation of novel genetic resources. Many traits have been reported to have potential to enhance yield, and high expression of these can be found in germplasm collections. To boost yield in irrigated situations, spike fertility must be improved simultaneously with photosynthetic capacity. CIMMYT's Wheat Genetic Resources program has identified a source of multi-ovary florets, with up to 6 kernels per floret. Lines from landrace collections have been identified that have very high chlorophyll concentration, which may increase leaf photosynthetic rate. High chlorophyll concentration and high stomatal conductance are associated with heat tolerance. Recent studies, through augmented use of seed multiplication nurseries, identified high expression of these traits in bank accessions, and both traits were heritable. Searches are underway for drought tolerance traits related to remobilization of stem fructans, awn photosynthesis, osmotic adjustment, and pubescence. Genetic diversity from wild relatives through the production of synthetic wheats has produced novel genetic diversity.
