Crop Science

Published by Crop Science Society of America
Online ISSN: 1435-0653
Publications
Article
'Tousan 140' and 'Hourei', two soybean [Glycine max (L) Merr.] accessions from Japan, each possess a single gene at different loci for resistance to Japanese Soybean mosaic virus (SMV) strain SMV C. However, more genetic information is needed to utilize these lines in a breeding program. The objectives of this study were to determine (i) the reaction of Tousan 140 and Hourei to SMV-G1 through G7 strains, (ii) the inheritance of SMV resistance in Tousan 140 and Hourei to strains SMV-G1 and G7, and (iii) the allelomorphic relationship of resistance genes in these accessions with previously known resistance genes. Tousan 140 and Hourei were crossed with SMV susceptible cultivar Lee 68 to study the inheritance of resistance. They were also crossed with lines possessing Rsv1, Rsv3, and putative Rsv4, and to each other, to elucidate the allelomorphic relationships among the genes in Tousan 140, Hourei, and previously reported genes. Inheritance and allelism studies indicated that Tousan 140 possesses two SMV resistance genes. These two genes were separated in two F(2:3) lines. One of the genes, an allele of Rsv1, expresses resistance to SMV-G1 through G3 and susceptibility to SMV-G5 through G7 while the other one, an allele of Rsv3, expresses resistance to SMV-G5 through G7 and susceptibility to SMV-G1 through G3. Their presence in Tousan 140 makes it resistant to strains SMV-G1 through G7. Hourei also is resistant to SMV-G1 through G7 and possesses two SMV resistance genes, which are also alleles of Rsv1 and Rsv3. One, probably the Rsv1 allele, expresses resistance to SMV-G1 and G7 and the other, probably the Rsv3 allele, expresses resistance to SMV-G7, but is susceptible to G1.
 
Article
The Oklahoma Agric. Exp. Station recently released six broad genetic base alfalfa germplasms that trace to hundreds of world collection accessions (P.I.'s) crossed with adapted material and possess varying degrees of enhancement for adaptation (1). With the exception of OK 208, these germplasms were synthesized using several thousand plants tracing from intercrossed P.I.'s selected through phenotypic selection for resistance to the blue alfalfa aphid (Acyrthosiphon kondoi) collected in Oklahoma during 1984-1990 period. OK 208 was developed by phenotypic selection for blue alfalfa aphid biotype BAOK90 (3) resistance in 1996. The purpose of this breeding approach is to improve the utility of P.I.'s for development of alfalfa cultivars. These populations have a highly diverse parentage and carry alleles not normally possessed by cultivars and experimental strains in traditional breeding programs. Their adapted parents contributed varying degrees of adaptation, and they provide resistance to important pests including fusarium wilt (Fusarium oxysporum), bacterial wilt (Clavibacter michiganensis), phytophthora root rot (Phytophthora megasperma), anthracnose (Colletotrichum trifolii), verticillium wilt (Verticillium albo-atrum), spotted alfalfa aphid (Therioaphis maculata), blue alfalfa aphid, and pea aphid (A. pisum). Six intermediate populations were created by intercrossing one to four to blue alfalfa aphid-resistant plants from many of the several hundred accessions from the USDA-ARS world alfalfa collection. Overall, 926 accessions were screened. (The complete list of P.I.'s that contributed to these germplasms can be found online at http://alfalfa.okstate.edu/alfalfa/pub/PI-accessions.htm.) An equal blend of seed from these populations was planted in an isolated field in rows (1 m apart) alternating with Cimarron, a well-adapted, high yielding, persistent cultivar. Wild bees were used to pollinate. Each world collection plant grew and produced seed with Cimarron plants on either side for convenient movement of pollinators, promoting crossing between P.I.'s and plants of the adapted cultivar. Syn 1 seed was harvested separately from each row, resulting in two populations: OK 163, which had P.I.'s as the female parent, and OK 164, which had Cimarron as the female parent. OK 163 seed was then sown in alternate rows with OK 169 syn 1 (2), a broad genetic based adapted strain. Seed was produced, and as before, two populations were harvested. Seed harvested from OK 163 rows was designated OK 187 syn 1, and seed harvested from OK 169 rows was designated OK 188 syn 1. Approximately 1000 plants each of OK 163 and OK 164 underwent two additional cycles of selection for resistance to the blue alfalfa aphid collected in Oklahoma. The 112 resulting plants were interpollinated in the greenhouse by hand to form OK 208 syn 1. Generally, broad genetic based populations are completely unadapted for forage production and have little agronomic value without enhancement. These populations were subjected to natural selection during field seed production, which required living through at least one winter and summer in Oklahoma. They have been enhanced also with alleles from well-adapted cultivars to varying degrees. Forage yield of the enhanced strains is equal to or better than most of the entries in the Oklahoma variety testing program, including some of the best material developed by public and private breeding programs.
 
Article
Drought stress may alter protein synthesis in turfgrasses. The objectives of this study were to investigate physiological changes associated with the synthesis of dehydrin and a cytosolic-heat shock protein (HSC 70) in response to drought stress in two tall fescue (Festuca arundinacea L.) cultivars, 'Southeast' and 'Rebel Jr.'. The effects of abscisic acid (ABA) application on the drought tolerance of the cultivars also were evaluated. The cultivars were subjected to three treatments in growth chambers: well-watered control, drought stress, and drought stress following ABA treatment. Turf quality and leaf relative water content (RWC) decreased and electrolyte leakage (EL) increased during drought stress for both cultivars. The ABA-treated plants maintained higher turf quality and RWC, and lower EL than untreated plants under drought stress conditions. Levels of 20- and 29-kDa polypeptides increased during drought stress, and a 35-kDa polypeptide was noted in both cultivars only when subjected to drought stress either with or without ABA treatment. Immunoblot analysis indicated that dehydrin-like polypeptides of about 23-60 kDa were induced by progressive water deficit in both cultivars. The 53 kDa dehydrin polypeptide was present in Southeast with or without ABA treatment at 10 d of drought stress, whereas the 40 kDa dehydrin polypeptide accumulated in Rebel Jr. in both treatment. The 23- and 27-kDa dehydrin polypeptides were present at 10 d in drought-stressed and ABA-treated plants in both cultivars, but were more pronounced in the drought-stressed plants without ABA. A cytosolic-heat shock protein (HSC 70) was detected in plants in all treatments including well-watered plants of both cultivars, but its levels were higher in drought-stressed and ABA-treated plants. No single dehydrin polypeptide was induced by ABA treatment under drought stress, however, the promotive effects of ABA on the reduced drought stress paralleled the delayed induction of protein synthesis in tall fescue.
 
Article
The sorghum germplasm collection currently contains over 42 000 accessions, a number that is too large to manage efficiently. The specific objective of this research was to compare clusters developed from agronomic descriptors with phylogenetic groupings based on random amplified polymorphic DNA (RAPD) fingerprinting of selected sorghum [Sorghum bicolor (L.) Moench] races. Our intent was to identify one approach using agronomic descriptors that would most closely approximate the groupings produced by RAPD markers. Ninety-four accessions of sorghum were grouped into four of the five major races. Differences among accessions determined by various clustering procedures based on agronomic characteristics were compared with clusters developed by means of RAPD markers. Each race varied in the degree of similarity between the four clustering approaches taken and the information provided by RAPD fingerprinting. Test 2, standardization of data by Z-scores and cluster analysis using the complete set of data, provided the highest similarity score for the race bicolor, while Test 3, standardization of data by Z-scores and cluster analysis based on a reduced set of variables selected from principle component analysis, provided the highest similarity scores for the races guinea. Test 1, random selection, was highest for the races caudatum and durra. When averaged over all the races, Test 2 provided the highest similarity score. The results of this study indicate that no one approach to develop clusters by means of agronomic descriptors closely approximate the groupings produced by RAPD markers. These results underscore the need for further research in the evaluation of techniques used to develop core collections and their validity.
 
Article
Genetic improvement in yield is conditional on surmounting yield-limiting factors. Nitrogen (N) has been considered an important limiting factor to soybean [Glycine max (L.) Merr.] yield. The high demand for N by soybean seed was previously considered to lead to early leaf senescence through accelerated remobilization of N from the vegetative tissue. The consequent reduction in photosynthetic capacity was postulated to limit yield. The objectives of the current experiment were to determine the changes in N accumulation, remobilization, and partitioning associated with genetic yield improvement. Two groups of old, low-yielding ('Pagoda' and 'Mandarin Ottawa') and new, high-yielding ('Maple Glen' and 'OAC Bayfield') soybean cultivars of similar maturity were grown in side-by-side trials at the Elora Research Station, Ontario, in 1996 and 1997. Nitrogen and dry matter accumulation in leaf, stem + petiole, roots, and seeds were determined during the growing season. The newer cultivars had higher yields and higher seed N content. Contrary to the postulated association between leaf senescence and leaf N values, neither leaf N concentration nor leaf N content per unit leaf area (at R6) were association consistently with either yield or leaf area duration (LAD). Although most of the N in the seed was derived from N remobilized from vegetative tissue, the newer cultivars with their higher yields and LAD, remobilized no more N out of the vegetative tissue than did older, lower-yielding ones. The newer cultivars were distinct from their older counterparts in their ability to accumulate more N during the seed filling period (SFP). Genetic improvement of the short-season soybeans tested was a consequence of continued N accumulation during the SFP and was not due to differences in the genotype's capacity to remobilize or partition N to the seed.
 
Article
Crop model testing in diverse environments is essential if modelers wish to make applications or extrapolations to those environments. A recent study demonstrated the effectiveness of optimization techniques for deriving cultivar coefficients for the CROPGRO-Soybean model from typical information provided by soybean performance tests. The objectives of this study were (i) to explore the extent to which cultivar coefficients developed by these approaches from crop performance tests are stable across different regions, (ii) to test the CROPGRO-Soybean model's ability to predict phenology and seed yield using cultivar coefficients that were developed in different regions, and (iii) to investigate whether 3 yr of crop performance data are adequate for developing stable genetic coefficients. A stepwise procedure was applied to derive cultivar coefficients for 10 common cultivars grown in different environments in Georgia and North Carolina. Regarding the transportability of cultivar coefficients across states, we found that the critical daylength coefficients were the most reliable cultivar traits. We found less stability of the cultivar traits that control genetic differences in seed yield potential. The estimated cultivar coefficients developed in Georgia enabled CROPGRO to predict yield and harvest maturity in North Carolina within 3.8% and 3.5 d, respectively, from the observed averages. Using the cultivar coefficients developed from North Carolina environments allowed us to simulate the actual mean yield and harvest maturity in Georgia to within 2.5% and 2.0 d. Furthermore, the model's ability to predict seed yield and maturity with cultivar coefficients developed from 3 yr of data was nearly as good as that derived from much larger data sets.
 
Article
Understanding factors that affect flowering of crimson clover (Trifolium incarnatum L.) could improve management decisions to optimize utilization by improving season of use. The experiment was a split-plot randomized complete block design with three replications at College Station, TX, in the 1997-1998 and 1999-2000 growing seasons, and Overton, TX, in the 1998-1999 growing season. Main plot treatments of two crimson clover cultivars and subplot treatments of six planting dates (PDs) were used to evaluate the effect of date to reach 50% budding and 50% flowering based on day of year (DOY), days after planting (DAP), photothermal index (PTI), and growing degree days (GDD) under field conditions. Correlations with 50% bud and 50% flower were almost identical. 'Columbus' planted in the autumn flowered an average of 49 d later than 'Tibbee'. Date to reach 50% flowering was best correlated with DOY (r = 0.93 and 0.97) and DAP (r = 0.92 and 0.98) for Columbus and Tibbee. Date to reach flowering was not as highly correlated with PTI (r = 0.66 and 0.82) or GDD (r = 0.71 and 0.85) for Columbus and Tibbee, thus temperature could not be used to predict flowering. Planting after 21 December delayed flowering in Tibbee 2 to 9 wks, whereas, Columbus planted after 21 December did not flower. It is important to plant early in the growing season or to use later-maturing cultivars to maximize the length of the growing season and possible total production in grazed environments.
 
Article
Soybean plants [Glycine max (L.) Merr.] of the determinate cultivar Ransom growing in controlled environments under 16-h photoperiods were exposed to 10, 12, 14, 15, and 16-h photoperiods upon expansion of either the two primaries or fifth trifoliolate leaf (V1 and V6 developmental stages, respectively) to determine the influence of plant size on sensitivity to photoperiod. Plants were sampled at 2 to 3-day intervals over a 21-day treatment period and examined microscopically for evidence of floral development. Time of floral initiation for plants exposed to photoperiod treatments at either V1 or V6 stage varied only by a few days among photoperiods, but the subsequent differentiation of floral primordia was much more rapid at shorter than at longer photoperiods. These results confirm previous observations for plants transferred upon expansion of the first trifoliolate leaf (V2 stage) and indicate that sensitivity of floral responsiveness to photoperiod changed little with plant size.
 
Article
Agronomic and horticultural crop species experience reductions in growth and harvestable yield after exposure to physical agitation (also known as mechanical stress), as by wind or rain. A greenhouse study was conducted to test the influence of mechanical stress on soybean yield and to determine if exposure to mechanical stress during discrete growth periods has differential effects on seed yield. A modified rotatory shaker was used to apply seismic (i.e., shaking) stress. Brief, periodic episodes of seismic stress reduced stem length, total seed dry weight, and seed number of soybean [Glycine max (L.) Merr.]. Lodging resistance was greater for plants stressed during vegetative growth or throughout vegetative and reproductive growth than during reproductive growth only. Seed dry weight yield was reduced regardless of the timing or duration of stress application, but was lowest when applied during reproductive development. Seismic stress applied during reproductive growth stages R1 to R2 (Days 3 to 4) was as detrimental to seed dry weight accumulation as was stress applied during growth stages R1 to R6 (Days 39 to 42). Seed dry weight per plant was highly correlated with seed number per plant, and seed number was correlated with the seed number of two- and three-seeded pods. Dry weight per 100 seeds was unaffected by seismic-stress treatment. Growth and yield reductions resulting from treatments applied only during the vegetative stage imply that long-term mechanical effects were induced, from which the plants did not fully recover. It is unclear which yield-controlling physiological processes were affected by mechanical stress. Both transient and long-term effects on yield-controlling processes remain to be elucidated.
 
The origin of mutant soybean lines with different fatty acid composition. The major alleles controlling the genotype of the mutant soybeans are given in bold. 
Location effects accounted 
Combined analysis of variance and estimate of variance components (VC) for fatty acid composition over 17 genotypes and 12 environments. 
Article
There has been a major effort to produce soybean [Glycine max (L.) Merr.] lines with modified fatty acid profiles in order to improve quality and develop new uses for soybean oil. Utilization of the lines depends on their agronomic traits and stability of the fatty acid profiles in diverse environments. The objectives of this study were to (i) evaluate the influence of years and locations on the fatty acid composition of soybean genotypes with unique fatty acid profiles, (ii) determine which fatty acids and fatty acid profiles are the most stable, and (iii) evaluate agronomic and seed quality traits of mutant soybean lines. Genotypes were evaluated over three years (1996, 1997, and 1998) at four locations in Southern Ontario, Canada. Year effects had the largest impact on all fatty acid levels. Location effects were significant only for oleic and linolenic acids. Genotype x year interaction effect was significant for all fatty acids whereas genotype x location and genotype x year x location interaction effects were significant only for oleic, linoleic, and linolenic acids. Mutants with reduced or elevated palmitic, elevated oleic, or reduced linolenic acid concentrations exhibited average or higher stability than lines with normal levels of these fatty acids. Therefore, these lines may be suitable for growing in a wide range of environments. Maturity, plant height, lodging, seed size, and seed quality were significantly different between mutants and cultivars. Seed yield was significantly reduced in mutants compared to cultivars.
 
Article
The taxonomic classification of the genus Agrostis is one of the most complicated of the grass genera. Classification based upon morphological and anatomical characters is difficult and complicated by the presence of intermediate forms and the misapplication of names. Determining ploidy levels of new germplasm can assist in species determination and is necessary before initiating breeding or genetics studies. The objectives of this study were to (i) evaluate the use of laser flow cytometry as a quick, reliable tool to determine ploidy level and aid in Agrostis species determination, and (ii) identify morphological characters associated with DNA content or ploidy level. The six Agrostis species evaluated were A. canina L. subsp. canina, A. canina L. subsp. montana (Hartm.) Hartm., A. palustris Huds. [= A. stolonifera var. palustris (Huds.) Farw.], A. tenuis Sibth. (= A. capillaris L.), A. castellana Boiss. & Reut., and A. alba L. Ploidy level was determined by flow cytometry and root tip chromosome counts. Plant height, panicle height, flag leaf length, flag leaf width, and highest internode length of mature field-grown spaced plants were measured. Significant differences in 2C DNA content were found between species (P < 0.01) differing in ploidy level. Flow cytometry was effective in differentiating between diploid, tetraploid, and hexaploid species. Chromosome numbers previously reported and those observed in this study were positively correlated with 2C nuclear DNA content (r = 0.98, P < 0.01). Flag leaf length was the only morphological measurement taken that was significantly positively correlated to DNA content (r = 0.98, P < 0.001). The results of this study indicate that laser flow cytometry is a quick, reliable tool to determine ploidy levels and infer certain species of AGROSTIS: This technique will aid breeders to quickly and accurately determine ploidy levels of new germplasm collections.
 
Results of multidimensional scaling of preference observations 
Composition of alfalfa hays fed to goats in Exp. 2. 
Article
Diurnal variation in the concentration of total nonstructural carbohydrates (TNC) occurs in plants as a result of photosynthesis. Ruminants have been shown to prefer tall fescue (Festuca arundinacea Schreber) hays cut in the afternoon but the effect of morning vs. evening cutting had not been tested in legumes. To test for diurnal variation in preference for alfalfa (Medicago sativa L.), we harvested six times in the midbud stage. Harvests were paired so that each time a cutting of alfalfa was made at sundown (PM) another was made the next morning at sunup (AM). We harvested in this manner three times resulting in six hays. The hays were field dried, baled, and chopped prior to their use 3 to 6 mo after harvest. Three experiments were conducted [Exp. 1, sheep (Ovis aries); Exp. 2, goats (Capra hircus hircus); and Exp. 3, cattle (Bos taurus)] utilizing six animals in each case. During an adaptation phase, hays were offered alone as meals. In the experimental phase, every possible pair of hays (15 pairs) was presented for a meal. Data were analyzed by multidimensional scaling as well as by traditional analyses. Multidimensional scaling indicated that the animals were basing selection on at least two criteria. Variables associated with preference through multiple regression varied across experiments but significant coefficients were found between preference and nitrate, protein, carbohydrate fractions, lignin, and cellulose. Coefficients varied depending on which other variables were in the model; however, carbohydrates were associated with positive coefficients. Shifting hay mowing from early in the day to late in the day was effective in increasing forage preference as expressed by short-term dry matter intake.
 
Article
Seed yield of alfalfa (Medicago sativa L.) is important in determining the effective distribution of new cultivars to farmers. Many genetic and environmental factors affect seed yield. This study was conducted to explain seed yield variation induced by either environmental conditions or cultivars. We analyzed seed yield, aboveground phytomass, harvest index, and seed yield components for a set of 12 cultivars at four locations across France in each of three years. Each location x year combination was considered an environment. Seed weight, number of pods per inflorescence, number of seeds per pod, and mean seed weight were measured. Mean seed yield was 801 kg ha(-1). Large variation in seed yield was found among cultivars and environments. The cultivar x environment interaction was significant. Among environments, seed yield was highly correlated with aboveground phytomass at harvest (r = 0.94) as the lowest seed yields were obtained in the seeding year. The cultivars most adapted to grazing showed the lowest seed yields. Seed yield was genetically correlated with lodging resistance (r = -0.89) and harvest index (r = 0.99). The mean harvest index was 12.7%. The seed weight per inflorescence showed a high broad-sense heritability (0.58) and a high genetic correlation with seed yield (r = 0.91) and with harvest index (r = 0.96). Variation in seed weight per inflorescence was associated with variation in the number of seeds per pod and number of pods per inflorescence. Seed weight per inflorescence appears to have a strong genetic association with seed yield in alfalfa. Environments with high aboveground phytomass potential also have high seed yield potential.
 
Herbage ergovaline and peramine concentrations as functions 
Article
Endophytic fungi in pasture grasses produce alkaloids which affect invertebrate and vertebrate herbivores. While the competence to produce an alkaloid is a property of the fungus, the host plant may moderate fungal activity. Host genetic influence on endophyte activity was studied in perennial ryegrass (Lolium perenne L.) infected with a common strain of Neotyphodium lolii (Latch, Christensen & Samuels) Glenn, Bacon & Hanlin. Progeny seedling families of a partial diallel cross and their 12 parent clones were compared in a glasshouse experiment. Peramine and ergovaline concentrations were determined by high pressure liquid chromatography (HPLC), and intensity of endophyte infection was determined by enzyme-linked immunosorbent assay (ELISA). Concentrations of peramine and ergovaline and the amount of endophyte mycelium in plants varied between families, consistently across two glasshouse cells and (for the HPLC data) two harvests. There was no indication of any maternal effects. Host genetic control was evident in significant general combining ability effects and smaller specific combining ability effects. Parent-progeny correlation coefficients were high, and narrow-sense heritability was estimated as 0.70, 0.72, and 0.58 respectively for ergovaline, peramine, and ELISA. Further analysis indicated little interaction between loci, and no directional dominance. The three traits were correlated, indicating that 41 and 65% of the genetically controlled variation in ergovaline and peramine concentrations, respectively, was a function of mycelial mass. However, there were departures from these relationships. Host plant selection may enable development of pastures with controlled low levels of toxic but ecologically beneficial endophyte metabolites.
 
Article
Dwarf plants are useful in research because multiple plants can be grown in a small area. Rice (Oryza sativa L.) is especially important since its relatively simple genome has recently been sequenced. We are characterizing a gibberellic acid (GA) mutant of rice (japonica cv 'Shiokari,' line N-71) that is extremely dwarf (20 cm tall). Unfortunately, this GA mutation is associated with poor germination (70%) under aerobic conditions. Neither exogenous GA nor a dormancy-breaking heat treatment improved germination. However, 95% germination was achieved by germinating the seeds anaerobically, either in a pure N2 environment or submerged in unstirred tap water. The anaerobic conditions appear to break a mild post-harvest dormancy in this rice cultivar.
 
Article
In the rainfed lowlands, rice (Oryza sativa L.) develops roots under anaerobic soil conditions with ponded water, prior to exposure to aerobic soil conditions and water stress. Constitutive root system development in anaerobic soil conditions has been reported to have a positive effect on subsequent expression of adaptive root traits and water extraction during water stress. We examined effects of phenotyping environment on identification of quantitative trait loci (QTLs) for constitutive root morphology traits using 220 doubled-haploid lines (DHLs) from the cross of 'CT9993-5-10-1-M' (CT9993; japonica, upland adapted) x 'IR62266-42-6-2' (IR62266; indica, lowland adapted) in four greenhouse experiments. Broad sense heritability (h(2)) was 75, 60, and 64% on average for shoot biomass, deep root morphology, and root thickness traits, respectively. Quantitative trait loci analysis identified 18 genomic regions associated with deep root morphology traits, but only three were identified consistently across experiments. Three out of a total of eight QTLs for root thickness traits were found in more than one experiment. The maximum genetic effects caused by a single QTL were increments of 0.05 g of deep root mass below a 30-cm soil depth, 0.9% of deep root ratio, 1.6 cm of rooting depth, and 0.09 cm of root thickness, with phenotypic variation explained by a single QTL ranging from 6.8 to 51.8%. The results demonstrate the importance of phenotyping environment and suggest prospects for selection of QTLs for deep root morphology, root thickness, and vigorous seedling growth under anaerobic conditions to improve the constitutive root system of rainfed lowland rice. There was some consistency in QTL regions identified, despite the presence of QTL x environment interactions.
 
Effects of SMV (strain G2) infection at the V8 growth stage  
Effect of inoculation with Soybean mosaic virus (SMV) on the duration of plant reproductive development in Experiment I.
Relationship between the incidence of Phomopsis spp. seed  
Effects of SMV (strain G6) infection at the V8 growth stage,  
Weather conditions during seed development and maturation in Experiment I, 1996 and 1997. †
Article
Infection of soybean [Glycine max (L.) Merr.] plants with Soybean mosaic virus (SMV) has been reported to enhance Phomopsis spp. infection, which reduces seed quality. The timing and incidence of SMV infection depends largely upon the level of primary inoculum and aphid-activity. Two field experiments were conducted in aphid-free environments, to examine the influence of (i) SMV-infection, and (ii) SMV-resistance alleles of the Rsv(1) gene, on the incidence of Phomopsis spp. seed infection. In the first experiment, mock inoculated (potassium phosphate buffer) SMV-susceptible cultivars (Clark and Williams), and their SMV-resistant isolines (L78-434 and L78-379, with dominant Rsv(1) allele conferring resistance to SMV strains G1-G6), showed low levels (<10%) of Phomopsis spp. seed infection. In contrast, susceptible cultivars mechanically inoculated with SMV (G2 strain, V8 stage) exhibited a 3- to 8-fold increase in the incidence Phomopsis spp. seed infection. In the second experiment, mock inoculation of the susceptible cultivar, Clark, and two SMV-resistant lines (10-rsv(1)(y) and 18-rsv(1)(y), with recessive rsv(1)(y) allele conferring resistance to SMV strains G1-G3), resulted in <20% Phomopsis spp. seed infection. In contrast, those plants mechanically inoculated with SMV (strain G6, V8 stage) had significantly higher levels of Phomopsis spp. seed infection (52 to 78%). It is concluded that the lower incidence of Phomopsis spp. seed infection in SMV-resistant plants was not due to the SMV resistance alleles of the Rsv(1) gene per se, but rather due to the absence of SMV infection. Thus, the use of SMV-resistant varieties prevented/reduced SMV and Phomopsis spp. seed infection.
 
Article
Understanding factors that affect growth and development of crimson clover (Trifolium incarnatum L.) are important for the development of management practices to optimize forage utilization. In a 3-yr field experiment at College Station, TX, we evaluated the effects of planting date on rate of leaf appearance of an intermediate- and late-maturing crimson clover. We wanted to determine if growing degree days (GDD) or a photothermal index (PTI) could be used to predict growth. Leaf appearance rates (LAR) did not differ between 'Tibbee' and 'Columbus' crimson clover. Leaf appearance rate was primarily controlled by temperature or GDD, which accounted for 90 to 99% of the variability within each planting date. Photoperiod did not consistently influence the rate of leaf appearance under normal daylengths of 10 h 12 min to 14 h 6 min used in this study. Predictions of LAR were not improved when photoperiod was combined with temperature in a photothermal index than with predictions that used GDD alone. Leaf appearance rate of crimson clover was generally higher when planted in October, November, and December and lower when planted in September, February, and March.
 
Article
Seedling emergence is an important trait that can limit commercialization of sweet corn hybrids. This study was designed to test what effect beneficial QTL alleles that enhance seedling emergence exert when introgressed, using marker-assisted backcrossing, into sweet corn commercial germplasm. Three RFLP marker alleles linked to QTL that enhanced seedling emergence were identified in an F(2:3) sweet corn mapping population. A recombinant inbred line (RIL, F(8)) derived from this population was used as a donor parent to backcross the marker-QTL alleles into three elite commercial sweet corn inbreds. Plants in the three segregating BC(2) populations were crossed to the non-recurrent commercial inbreds to produce three BC(2)F(1) populations with families either segregating or lacking the marker donor allele(s). These three populations were evaluated for seedling emergence under field conditions in two successive years. Across the three populations, BC(2)F(1) families segregating for the donor QTL allele linked to the marker umc139 (on chromosome 2), bnl9.08 (on chromosome 8), or php200689 (on chromosome 1) displayed 40.8, 30.2, and 28.2% increases in seedling emergence, respectively, over the unmodified F(1)s. The introgressed QTL alleles were observed to enhance seedling emergence in the BC(2)F(1) generation as was observed in the original F(2:3) mapping population. Marker-QTL associated effects were reproducible across generations and populations indicating that QTL identified in one population can exert similar effects in different genetic backgrounds. Results suggest that using DNA marker technology can help to identify and introgress beneficial QTL alleles, shortening the time and resources required to develop improved germplasm.
 
Article
Ethylene (C2H4) gas is produced throughout the life cycle of plants and can accumulate in closed growth chambers to levels 100 times higher than in outside environments. Elevated atmospheric C2H4 can cause a variety of abnormal responses, but the sensitivity to elevated C2H4 is not well characterized. We evaluated the C2H4 sensitivity of wheat (Triticum aestivum L.) and rice (Oryza sativa L.) in five studies. The first three studies compared the effects of continuous C2H4 levels ranging from 0 to 1000 nmol mol-1 (ppb) in a growth chamber throughout the life cycle of the plants. A short-term 1000 nmol mol-1 treatment was included in which exposure was stopped at anthesis. Yield was reduced by 36% in wheat and 63% in rice at 50 nmol mol-1 and both species were virtually sterile when continuously exposed to 1000 nmol mol-1. However, the yield reductions were much less with exposure that stopped at anthesis, suggesting the detrimental effect of C2H4 on yield was greatest around the time of seed set. Two additional studies evaluated the differential sensitivity of two wheat cultivars (Super Dwarf and USU-Apogee) to 50 nmol mol-1 C2H4 at three CO2 levels [350, 1200, 5000 micromoles mol-1 (ppm)] in a greenhouse. Yield of USU-Apogee was not significantly reduced by C2H4 but the yield of Super Dwarf was reduced by 60%. Elevated CO2 did not influence the sensitivity to C2H4. A difference in the C2H4 sensitivity of USU-Apogee between greenhouse and growth chamber trials suggests that C2H4 sensitivity is dependent on the environment. Collectively, the data suggest that relatively low levels of C2H4 could induce anomalous plant responses by accumulation in greenhouses and growth chambers with inadequate ventilation. The data also suggest that C2H4 sensitivity can be reduced by both genetic and environmental manipulations.
 
Article
Yield of water-limited crops is determined by crop water use and by plant water use efficiency, each of which will be affected by the anticipated rise in atmospheric carbon dioxide (CO(2)) concentration and concomitant increase in temperature. At the leaf level, a given proportional increase in CO(2) concentration generally elicits a similar relative increase in transpiration efficiency (ratio of net photosynthesis to transpiration). The increase in transpiration efficiency may result both from an increase in photosynthetic rate and a decrease in stomatal conductance. Feedbacks involved in scaling from leaf to crop constrain the increase in net carbon gain and reduce the anti-transpiration effect of CO(2) enrichment. As a result, the increase in crop water use efficiency at high CO(2) typically is less than 75% of that measured at the leaf level. By accelerating crop development and reducing harvest index, higher temperatures often erode yield benefits of improved water use efficiency at high CO(2). The fraction of available water that is used by crops could increase with CO(2) concentration because of greater root growth and faster canopy closure, but these effects have received scant study. Field experiments indicate that CO(2) enrichment will increase crop water use efficiency mainly by increasing photosynthesis and growth. Yield should be most responsive to CO(2) when temperatures approximate the optimum for crop growth. Elevating CO(2) can ameliorate negative effects of above-optimal temperatures, but temperatures near the upper limit for crops will depress yields irrespective of CO(2) concentration.
 
Dendrograms from clustering 16 locations of the Uniform Southern Soft Red Winter Wheat Nursery in 1992-1994 for (a) flour yield, protein content, alkaline water retention capacity, and softness equivalence; (b) flour yield, protein content, and alkaline water retention capacity. 
Zones for soft red winter wheat in South-Eastern Region from 
Article
Division of regional nursery test sites into homogenous subregions contributes to more efficient evaluation and better differentiation of cultivars. Data from the Uniform Southern Soft Red Winter Wheat Nursery (USSRWWN) were analyzed to group testing sites into relatively homogenous subregions for milling and baking quality (MBQ) attributes. Environmental effects due to years accounted for over 50% of the total variation for protein content (P) and 42% for alkaline water retention capacity (AWRC). Genotype effect accounted for 63% of the total variation for softness equivalence (SE), and 37% for flour yield (FLY). A significant genotype x location (GxL) interaction occurred for FLY and P. However, the GxL variance component accounted for a small proportion of the total phenotypic variance, suggesting that clustering would be more beneficial for resource efficiency than for increasing differentiation of genotypes. A hierarchical cluster analysis was used to group locations on the basis of GxL interaction effects for FLY, P, AWRC, and SE. Cluster analysis divided the USSRWWN into two main subregions within which the GxL interaction was reduced by over 90% for FLY and by 60% for P. Although this classification is not entirely consistent with the geographic distribution of locations, clusters do follow general geographic-climatic-disease regions. Our results suggest that the USSR-WWN can be divided into subregions to reduce the resources expended on evaluation of MBQ attributes. This classification of locations could be useful in breeding for specific adaptability within subregions.
 
Article
Genetic engineering is becoming a useful tool in the improvement of plants and plant-based raw materials. Varieties with value-added traits are developed for nonfood use in industrial and medical production, and different production lines must be kept separate. For good management practices, knowledge of relevant gene flow parameters is required. In the present study, pollen-mediated dispersal of transgenes via cross-fertilization was examined. A transgenic barley (Hordeum vulgare L.) line carrying a marker gene coding for neomycin phosphotransferase II (nptII) was used as a pollen donor. For maximum resolution, a cytoplasmically male-sterile barley line was utilized as recipient and the flow of nptII transgene was monitored at distances of 1, 2, 3, 6, 12, 25, 50, and 100 m from the donor plots of 225 and 2000 m(2). Male-fertile plots at a distance of 1 m were included to measure the transgene flow in normal barley. The number of seeds obtained from male-sterile heads diminished rapidly with distance and only a few seeds were found at distances of 50 and 100 m. Molecular genetic analysis (polymerase chain reaction-PCR) revealed that all seeds obtained from male-sterile heads at a distance of 1 m were transgenic, as anticipated. However, only 3% of the distant seeds (50 m) actually carried the transgene, whereas most of them resulted from fertilization with nontransgenic background pollen. This background pollen was mainly due to pollen leakage in some male-sterile heads. In normal male-fertile barley, the cross-fertilization frequency with transgenic pollen varied from 0 to 7% at a distance of 1 m, depending on weather conditions on the heading day. We conclude that, because of competing self-produced and nontransgenic background pollen, the possibility of cross-pollination is very low between a transgenic barley field and an adjacent field cultivated with normal barley. However, adequate isolation distances and best management practices are needed for cultivation of transgenic barley.
 
Article
Phenological development affects canopy structure, radiation interception, and dry matter production; most crop simulation models therefore incorporate leaf emergence rate as a basic parameter. A recent study examined leaf emergence rate as a function of temperature and daylength among wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cultivars. Leaf emergence rate and phyllochron were modeled as functions of temperature alone, daylength alone, and the interaction between temperature and daylength. The resulting equations contained an unwieldy number of constants. Here we simplify by reducing the constants by > 70%, and show leaf emergence rate as a single response surface with temperature and daylength. In addition, we incorporate the effect of photosynthetic photon flux into the model. Generic fits for wheat and barley show cultivar differences less than +/- 5% for wheat and less than +/- 10% for barley. Barley is more sensitive to daylength changes than wheat for common environmental values of daylength, which may be related to the difference in sensitivity to daylength between spring and winter cultivars. Differences in leaf emergence rate between cultivars can be incorporated into the model by means of a single, nondimensional factor for each cultivar.
 
Article
Drought is a major constraint to common bean (Phaseolus vulgaris L.) production worldwide. Our objectives were to (i) identify sources of drought resistant germplasm in common bean cultivars and (ii) compare drought resistant germplasm with lines selected from interracial and intergene pool populations. We included in this study 12 of the most promising drought resistant cultivars from race Durango and 11 from race Jalisco, nine drought resistant lines selected from interracial or intergene pool populations, and two drought resistant and two susceptible checks. The 36 genotypes were evaluated in drought-stressed (DS) and nonstressed (NS) environments in four cropping seasons between 1996 and 1998 at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia. Drought stress reduced seed yield by 53%, 100-seed weight by 13%, and days to maturity by 3%. Race Durango cultivars had higher yield, larger seed weight, and earlier maturity than race Jalisco cultivars in DS and NS environments. Large variations within the two races were found for the three traits. Drought resistant selected lines out-yielded drought resistant checks by 44% in DS and 15% in NS and cultivars from race Durango by 48% in DS and 30% in NS and race Jalisco by 96% in DS and 46% in NS environments. Seed yield in DS was correlated negatively with the percent reduction (PR) because of drought stress and drought susceptibility index (DSI), whereas a positive correlation existed between PR and DSI. Drought resistant selected lines and race Durango cultivars had similar maturity. Mean 100-seed weight of selected lines (23 g) was less than race Durango (34 g) and race Jalisco cultivars (29 g). While new sources of drought resistance could be identified in races Durango and Jalisco, these drought resistant germplasm and selected lines derived from interracial and intergene pool populations should be utilized for improvement of drought resistance in common bean.
 
Article
Bermudagrass, Cynodon dactylon (L.) Pers., suffers periodic severe winter-kill throughout much of its area of use in the contiguous USA. A research goal is to increase freeze tolerance in cultivars to lessen the risk of such damage. An identified research need is for Cynodon germplasm resources to be characterized for freeze tolerance and hybridization potential. Accordingly, the objective of this research was to characterize the relative freeze tolerance of selected fertile bermudagrass plants. Nine tetraploid (2n = 4x = 36) C. dactylon and two triploid (2n = 3x = 27) hybrid (C. dactylon x C. transvaalensis Burtt Davy) clonal plants (standards) were evaluated in two experiments. Plants were propagated clonally and established in Cone-tainers (Ray Leach Cone-tainer Nursery, Canby, OR) for about 10 wk. Acclimation took place for 4 wk in controlled environment chambers at 8/2 degrees C (day/night) temperatures with a 10-h photoperiod. Following acclimation, Cone-tainers were placed into a freeze chamber and cooled rapidly to -2 degrees C, induced to freeze with ice chips, then held overnight at -2 degrees C. The freeze chamber was then programmed to cool linearly at 1 degrees C per hour. For each cultivar, three Cone-tainers were removed at each test temperature. Following thawing, Cone-tainers were transferred to a greenhouse and regrowth was evaluated visually. Nonlinear regression was used to estimate T(mid), which corresponded to the midpoint of the sigmoidal response curve of survival vs temperature. Within experiment one, Tifgreen (T(mid) = -7.2 degrees C) was significantly less cold hardy than Quickstand (-9.0 degrees C), A-12204 (-9.2 degrees C), Midiron (-9.9 degrees C), and A-12195 (-10.5 degrees C). A-12195 was significantly hardier than all genotypes except Midiron. In the second experiment, Arizona Common (-6.6 degrees C), Tifgreen (-7.1 degrees C), and A-12205 (-7.1 degrees C) were less hardy than A-9959 (-8.7 degrees C), A-12156 (-8.9 degrees C), A-12198 (-9.5 degrees C), and Midiron (-10.0 degrees C). Midiron was hardier than all genotypes except A-12198. The range of test temperatures chosen did not allow estimate of a T(mid) value for Zebra, but nearly 50% of the plants were killed at -6.0 degrees C.
 
Article
Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John's wort (Hypericum perforatum L. 'Helos'). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John's wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin-hypericin in St. John's wort, although there was a trend toward higher concentrations in the flax straw treatment.
 
Article
Current technologies for measuring plant water status are limited, while recently remote sensing techniques for estimating N status have increased with limited research on the interaction between the two stresses. Because plant water status methods are time-consuming and require numerous observations to characterize a field, managers could benefit from remote sensing techniques to assist in irrigation and N management decisions. A 2-yr experiment was initiated to determine specific wavelengths and/or combinations of wavelengths indicative of water stress and N deficiencies, and to evaluate these wavelengths for estimating in-season biomass and corn (Zea mays L.) grain yield. The experiment was a split-plot design with three replications. The treatment structure had five N rates (0, 45, 90, 134, and 269 kg N ha(-1)) and three water treatments [dryland, 0.5 evapotranspiration (ET), and full ET]. Canopy spectral radiance measurements (350-2500 nm) were taken at various growth stages (V6-V7, V13-V16, and V14-R1). Specific wavelengths for estimating crop biomass, N concentration, grain yield, and chlorophyll meter readings changed with growth stage and sampling date. Changes in total N and biomass in the presence of a water stress were estimated using near-infrared (NIR) reflectance and the water absorption bands. Reflectance in the green and NIR regions were used to estimate total N and biomass without water stress. Reflectance at 510, 705, and 1135 nm were found for estimating chlorophyll meter readings regardless of year or sampling date.
 
Article
As population density (POP) increases in a soybean [Glycine max (L.) Merr.] crop, maximum light interception (LI) occurs earlier in the season. Earlier canopy closure would be expected to increase the cumulative radiation intercepted. We hypothesized that if radiation use efficiency (RUE) was constant across a range of population densities in a nonstressful environment, then increasing POP would increase biomass at the end of the season. To test this hypothesis, we evaluated the response of total biomass produced during the season to cumulative intercepted photosynthetically active radiation (PAR) in field experiments at Fayetteville, AR, with soybean cultivars selected from Maturity Groups (MGs) 00 to IV. Additionally, from field experiments at Keiser, AR, with MG IV soybean cultivars, we assessed the response of RUE to POP. At both locations with MG IV cultivars, a late sowing date shortened the life cycle of the crop by 13 to 25 d compared with an early sowing date, resulting in less PAR accumulated. Similarly, early maturing cultivars had less time for PAR and biomass accumulation relative to later maturing cultivars. At Keiser, in three of the four environments, RUE decreased linearly by 26 to 30% as the POP increased from 7 to 135 plants m(-2). Final biomass at the end of the season, as a function of PAR accumulated from emergence to the full-seed-size stage of development, responded linearly to intercepted PAR up to approximately 400 MJ m(-2). Above 400 MJ m(-2), the response was curvilinear with little increases in biomass >700 MJ m(-2). Our data clearly indicate that RUE decreased as POP increased and that maximum biomass production in these environments was not limited by intercepted PAR.
 
Yearly GGE biplots for yield data from 1994–1999 soybean trials in the 2800 corn heat unit area of Ontario. The names of the test sites are spelled out in lowercase letters, with the first letter indicating the exact position of the site; the vertex genotypes are spelled out in uppercase letters, and all other genotypes are represented by " c " .  
GGE biplot based on the yield data of 28 soybean genotypes that were tested all three years from 1997–1999. (A) The genotype by environment biplot taking each year-site combination as a single environment; (B) the genotype by site biplot on the basis of data averaged over years. The names of the test sites are in lowercase letters and the names of the genotypes in uppercase letters. EXET Exeter, STPA St. Pauls, WINC Winchester, and WDST Woodstock.  
The yearly soybean genotype by trait biplots of 1994–1999. The traits are spelled out in lowercase letters, and each genotype is represented by " c " . DTM days to maturity, HEIGHT Plant height, KW 100 seed weight, LODG lodging scores, OIL percentage of oil, PROTEIN percentage of protein, YLD seed yield, YOIL oil yield per unit land area, and YPROT protein yield per unit land area.  
The polygon view of the genotype by trait biplot for 1999, demonstrating soybean genotype comparison on the basis of a GT biplot. DTM days to maturity, HEIGHT Plant height, KW 100 seed weight, LODG lodging scores, OIL percentage of oil, PROTEIN percentage of protein, YLD seed yield, YOIL oil yield per unit land area, and YPROT protein yield per unit land area.  
Soybean Genotype selection on the basis of a GT biplot. (A) Selection on the basis of seed yield; (B) selection on the basis of oil and protein concentration; (C) selection on the basis of oil concentration and seed yield; (D) selection on the basis of protein concentration and seed yield; and (E) selection on the basis of oil yield and protein yield. DTM days to maturity, HEIGHT Plant height, KW 100 seed weight, LODG lodging scores, OIL percentage of oil, PROTEIN percentage of protein, YLD seed yield, YOIL oil yield per unit land area, and YPROT protein yield per unit land area.  
Article
Superior crop cultivars must be identified through multi-environment trials (MET) and on the basis of multiple traits. The objectives of this paper were to describe two types of biplots, the GGE biplot and the GT biplot, which graphically display genotype by environment data and genotype by trait data, respectively, and hence facilitate cultivar evaluation on the basis of MET data and multiple traits. Genotype main effect plus genotype by environment interaction effect (GGE) biplot analysis of the soybean [Glycine max (L.) Merr.] yield data for the 2800 crop heat unit area of Ontario for MET in the period 1994-1999 revealed yearly crossover genotype by site interactions. The eastern Ontario site Winchester showed a different genotype response pattern from the three southwestern Ontario sites in four of the six years. The interactions were not large enough to divide the area into different mega-environments as when analyzed over years, a single cultivar yielded the best in all four sites. The southwestern site, St. Pauls, was found to always group together with at least one of the other three sites; it did not provide unique information on genotype performance. Therefore, in future cultivar evaluations, Winchester should always be used but St. Pauls can be dismissed. Applying GT biplot to the 1994-1999 multiple trait data illustrated that GT biplots graphically displayed the interrelationships among seed yield, oil content, protein content, plant height, and days to maturity, among other traits, and facilitated visual cultivar comparisons and selection. It was found that selection for seed yield alone was not only the simplest, but also the most effective strategy in the early stages of soybean breeding.
 
Biplot based on diallel data of seven wheat genotypes with varying resistance to Fusarium head blight; (A) average tester ordination view, (B) polygon view. Codes of the genotypes are: A ϭ Alidos, B ϭ 81-F3-79, C ϭ Arina, D ϭ SVP-72017-17-5-10, E ϭ SVP-C8718-5, F ϭ UNG-136.1, and G ϭ UNG-226.1. Genotypes are labeled with upper-case letters when viewed as entries and with lower-case letters when viewed as testers. Exact positions of the entries and testers are at the beginning of the labels. The circle indicates the average tester. 
Biplot based on diallel data of six wheat genotypes with varying resistance to Stagonospora nodorum blotch; (A) average tester ordination view, (B) polygon view. Codes of the genotypes are: A ϭ 18NT, B ϭ Coker9543, C ϭ Coker9803, D ϭ L890682, E ϭ TX82-11, and F ϭ TX92D7374. Genotypes are labeled with upper-case letters when viewed as entries and with lower-case letters when viewed as testers. Exact positions of the entries and testers are at the beginning of the labels. The circle indicates the average tester. 
Article
Diallel crosses have been used in genetic research to determine the inheritance of important traits among a set of genotypes and to identify superior parents for hybrid or cultivar development. Conventional diallel analysis is limited to partitioning the total variation of the data into general combining ability (GCA) of each genotype and specific combining ability (SCA) of each cross. In this paper we formulate a biplot approach for graphical diallel analysis. The biplot is constructed by the first two principal components (PCs) derived from subjecting the tester-centered diallel data to singular value decomposition. It displays the most important entry by tester patterns of the data and allows the following information to be extracted visually: (i) GCA of each genotype; (ii) SCA of each genotype; (iii) groups of parents with similar genetics; and (iv) superior hybrids. In addition, the biplot allows hypotheses to be formulated concerning the genetics of the genotypes. Three published diallel data sets of wheat (Triticum aestivum L.) and maize (Zea mays L.) were used to demonstrate the biplot approach and detailed procedures were provided for constructing and interpreting a biplot.
 
Article
Numerous studies have evaluated growth, stand dynamics, and botanical composition of grass swards separately, but little information is available on the interaction of these factors. The objectives of this study were to determine the response of growth rate, tiller density, and botanical composition in orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and timothy (Phleum pratense L.) to different N levels. Growth rates ranged from 8.6 to 1.54, 9.14 to 0.67, and 4.19 to 0.29 g dry matter (DM) m(-2) d(-1) in orchardgrass, smooth bromegrass, and timothy. Orchardgrass growth rates responded to changes in abiotic conditions, while smooth bromegrass and timothy expressed less plasticity under favorable growth environments. All species exhibited temporal fluctuations in tiller density. Orchardgrass and smooth bromegrass tiller densities were not closely associated with yield, presumably because of compensation in tiller weight. Nitrogen did not affect tiller density during the first production year, but orchardgrass tiller density was influenced by N throughout the second production year, including the fall growth period, when tiller density in all species was affected. Aggressive growth rates in orchardgrass reduced species diversity by 65% by the end of the second production year. Total diversity in smooth bromegrass decreased from 7.2 to 3.5 species 0.25 m(-2) compared with an increase in timothy from 1.5 to 5.7 species 0.25 m(-2) due to a combination of slow growth and reduced tiller density. Orchardgrass and smooth bromegrass are superior to timothy in Northeast hay production systems because of greater DM production and less weed competition.
 
Article
Genetic advances in grain yield under rainfed conditions have been achieved by empirical breeding methods. Progress is slowed, however, by large genotype x season and genotype x location interactions arising from unpredictable rainfall, which is a feature of dry environments. A good understanding of factors limiting and/or regulating yield now provides us with an opportunity to identify and then select for physiological and morphological traits that increase the efficiency of water use and yield under rainfed conditions. The incorporation of these traits into breeders' populations should broaden their genetic base. It also may lead to faster selection methods and selection for the traits may result in correlated gains in yield. Here, we undertake a review of factors that limit yield in rainfed environments and discuss genetic opportunities and genetic progress in overcoming them. The examples given are for wheat (Triticum aestivum L.), but the principles apply to all cereal crops grown in dry environments.
 
Shoot attributes of Gala grazing bromegrass, Matua praiFig. 2. Root attributes of Gala grazing bromegrass, Matua prairiegrass, and orchardgrass in the greenhouse and growth chamber. riegrass, and orchardgrass in the greenhouse and growth chamber. Each data point is the least-squares mean of 15 observations in Each data point is the least-squares mean of 15 observations in each experiment. Error bars are two standard error units. Some each experiment. Error bars are two standard error units. Some error bars may not be visible because they are smaller than the error bars may not be visible because they are smaller than the symbols. Numbers at each date indicate significant (P 0.05) symbols. Numbers at each date indicate significant (P 0.05) contrasts: (1) Matua prairiegrass and Gala grazing bromegrass vs. contrasts: (1) Matua prairiegrass and Gala grazing bromegrass vs. orchardgrass, and (2) Matua prairiegrass vs. Gala grazing bromeorchardgrass, and (2) Matua prairiegrass vs. Gala grazing bromegrass. grass. 
Leaf development of Gala grazing bromegrass, Matua prai 
Root attributes of grazing bromegrass, prairiegrass, and orFig. 4. Shoot attributes of grazing bromegrass, prairiegrass, and orchardgrass during 1999 in field plots at Rock Springs, PA. Each chardgrass during 1999 in field plots at Rock Springs, PA. Each data point is the least-squares mean of two planting dates, five data point is the least-squares mean of two planting dates, five replicates, and 15 seedlings per replicate. Error bars indicate two replicates, and 15 seedlings per replicate. Error bars indicate two standard error units. Some error bars may not be visible because standard error units. Some error bars may not be visible because they are smaller than the symbols. Numbers at each date indicate they are smaller than the symbols. Data were nonnormally distribsignificant (P 0.05) contrasts: (1) Dawn and Pennlate orcharduted and log10 transformed for analysis. Note that the y axis is on grass vs. other grasses, (2) Dawn vs. Pennlate, (3) Gala and Feeder a log10 scale. Numbers at each date indicate significant (P 0.05) grazing bromegrass vs. Matua and Luprime prairiegrass, (4) Lucontrasts: (1) Dawn and Pennlate orchardgrass vs. other grasses, prime vs. Matua, and (5) Feeder vs. Gala. (2) Dawn vs. Pennlate, (3) Gala and Feeder grazing bromegrass vs. Matua and Luprime prairiegrass, (4) Luprime vs. Matua, and (5) Feeder vs. Gala. 
Article
Seedling establishment is a critical phase in pasture management. Knowledge of the seedling development of new forages is necessary to develop management practices and recommend species mixtures for pasture seedings. We compared seedling growth and development of prairiegrass (Bromus willdenowii Kunth = B. catharticus Vahl), grazing bromegrass (B. stamineus Desv.), and orchardgrass (Dactylis glomerata L.) in controlled environment and field studies. Seedlings were sampled weekly for 7 wk in the growth chamber and greenhouse beginning 8 to 10 d after planting (DAP). The number and mass of leaves and roots were recorded. In the field, leaf development was measured during spring and fall of 1997, and leaf and root development were measured during spring and fall of 1999. Forage dry matter (DM) yield was measured in clipped field plots during 1998 to 2000. Grazing bromegrass had more leaves, about twice the number of tillers per seedling, and a greater seedling mass than other grasses. Grazing bromegrass also had 50 to 100% more tillers m(-2) than other grasses in clipped field plots. The larger seedling size and greater tiller density, however, did not translate into greater yield in clipped plots. Grazing bromegrass yielded 10 to 15% less than orchardgrass or prairiegrass. Because of their large seedlings and rapid development, prairiegrass and grazing bromegrass probably should be used at a lower seeding rate or perhaps not used in seed mixtures with small-seeded grasses. Seedlings of these grasses should be fully established by 40 to 50 DAP under favorable moisture and temperatures in the spring and late summer.
 
Article
Plants grown on porous media at elevated CO2 levels generally have low concentrations of tissue N and often appear to require increased levels of external N to maximize growth response. This study determines if soybean [Glycine max (L.) Merr. Ransom'] grown hydroponically at elevated CO2 requires increases in external NO3- concentrations beyond levels that are optimal at ambient CO2 to maintain tissue N concentrations and maximize the growth response. This study also investigates temporal influences of elevated CO2 on growth responses by soybean. Plants were grown vegetatively for 34 d in hydroponic culture at atmospheric CO2 concentrations of 400, 650, and 900 microliters L-1 and during the final 18 d at NO3- concentrations of 0.5, 1.0, 5.0 and 10.0 mM in the culture solution. At 650 and 900 microliters L-1 CO2, plants had maximum increases of 31 and 45% in dry weight during the experimental period. Plant growth at 900 microliters L-1 CO2 was stimulated earlier than at 650 microliters L-1. During the final 18 d of the experiment, the relative growth rates (RGR) of plants grown at elevated CO2 declined. Elevated CO2 caused increases in total N and total NO3(-)-N content and leaf area but not leaf number. Enhancing CO2 levels also caused a decrease in root:shoot ratios. Stomatal resistance increased by 2.1- and 2.8-fold for plants at the 650 and 900 microliters L-1 CO2, respectively. Nitrate level in the culture solutions had no effect on growth or on C:N ratios of tissues, nor did increases in CO2 levels cause a decrease in N concentration of plant tissues. Hence, increases in NO3- concentration of the hydroponic solution were not necessary to maintain the N status of the plants or to maximize the growth response to elevated CO2.
 
Final averages (+ SD) for environmental data for the four experimental runs.~" 
Potato stem dry weight in response to CO2 concentration at different photoperiods and photosynthetic photon flux (PPF) levels. 
Total plant dry weight of potato in response to CO 2 con- centration at different photoperiod and photosynthetic photon flux (PPP) levels. 
Article
Carbon dioxide concentration can exert a strong influence on plant growth, but this influence can vary depending on irradiance. To study this, potato plants (Solanum tuberosum L.) cultivars Norland', Russet Burbank', and Denali' were grown in controlled-environment rooms at different levels of CO2 and irradiance. Carbon dioxide levels were maintained either at 350 or 1000 micromoles mol-1 and applied in combination with 12- or 24-h photoperiods at 400 or 800 micromoles m-2 s-1 photosynthetic photon flux. Air temperatures and relative humidity were held constant at 16 degrees C and 70%, respectively, and plants were harvested 90 d after planting. When averaged across all cultivars, CO2 enrichment increased tuber yield and total plant dry weight by 39 and 34%, respectively, under a 12-h photoperiod at 400 micromoles m-2 s-1; 27 and 19% under 12 h at 800 micromoles m-2 s-1; 9 and 9% under 24h at 400 micromoles m-2 s-1. It decreased dry weights by 9 and 9% under 24 h at 800 micromoles m-2 s-1. Tuber yield of Denali showed the greatest increase (21%) in response to increased CO2 across all irradiance treatments, while tuber yields of Russet Burbank and Norland were increased 18 and 9%, respectively. The results show a pattern of greater plant growth from CO2 enrichment under lower PPF and a short photoperiod.
 
Article
Eastern gamagrass (Tripsacum dactyloides L.) is a warm-season, perennial grass with high palatability and productivity. However, poor stand establishment, often due to seed dormancy, limits its widespread use. Seed dormancy is often caused by structures surrounding the embryo, the physiological state of the embryo itself, or a combination of these factors. The eastern gamagrass dispersal unit is a floret within a thick, hard cupule. The objective of this study was to evaluate effects of cupule (including lemma and palea) removal and caryopsis scarification on germination of eastern gamagrass by means of different commercial seed lots produced in different locations and years. Germination tests were conducted at 20/30 degrees C alternating temperature with light during 30 degrees C for 8 h daily. Germination counts were made every 7 d. After 28 d, the germination of decupulated caryopses from different seed lots germinated from 16 to 49% across seed lots, compared with 5 to 18% germination for caryopses with cupule intact. Scarifying the pericarp over the embryo, however, resulted in germination of all dormant seeds. We conclude that while the cupule (including the lemma and palea) contributes to the dormancy of eastern gamagrass, the pericarp and/or testa are the main factors restricting germination of this species. In addition, caryopsis scarification increased the germination rate and the germination test could be shortened to 21 or even 14 d depending on the seed lot.
 
Article
The development of wheat (Triticum aestivum L.) cultivars that are resistant to Wheat streak mosaic virus (WSMV), yet competitive in yield under nondiseased conditions, is an objective for breeding programs in the Great Plains. This field study was conducted to compare classical and transgenic sources of resistance to WSMV. Three sets of germplasm were evaluated. These included adapted cultivars with various levels of tolerance, transgenic wheat lines containing viral coat protein or replicase sequences from WSMV that showed resistance in greenhouse trials, and germplasm with resistance to WSMV due to a translocated segment of chromosome 4Ai-2 from Thinopyrum intermedium (Host) Barkworth and Dewey containing Wsm1. A replicated field trial was conducted at Bozeman, MT, over a two-year period to evaluate the effectiveness of these different sources of resistance to mechanical inoculation of WSMV. Adapted cultivars differed in their ability to tolerate WSMV with mean reductions in yield over the two years ranging from 41 to 74%. Incorporation of the replicase or coat protein gene from WSMV did not provide field resistance to viral infection and in general, transgenic lines yielded less than their parent cultivar, 'Hi-Line'. Wheat-Thinopyrum lines positive for a DNA marker linked to the Wsm1 gene had significantly reduced yield losses ranging from 5 to 39% compared with yield losses of 57 to 88% in near isogenic lines not having the Wsm1 gene. Yield of lines with Wsm1 in the absence of disease ranged from 11 to 28% less than yield of lines without Wsm1. Our results suggest Wsm1 provides the best source of WSMV resistance but a yield penalty may exist because of the presence of the translocation.
 
Article
Information on gas exchange of crop stands grown in controlled environments is limited, but is vital for assessing the use of crops for human life-support in closed habitats envisioned for space. Two studies were conducted to measure gas exchange of wheat stands (Triticum aestivum L. cv. Yecora Rojo) grown from planting to maturity in a large (20 m2 canopy area), closed growth chamber. Daily rates of dark-period respiration and net photosynthesis of the stand were calculated from rates of CO2 build-up during dark cycles and subsequent CO2 drawdown in the light (i.e., a closed-system approach). Lighting was provided as a 20-h photoperiod by high-pressure sodium lamps, with canopy-level photosynthetic photon flux density (PPFD) ranging from 500 to 800 micromoles m-2 s-1 as canopy height increased. Net photosynthesis rates peaked near 27 micromoles CO2 m-2 s-1 at 25 d after planting, which corresponded closely with stand closure, and then declined slowly with age. Similarly, dark-period respiration rates peaked near 14 micromoles CO2 m-2 s-1 at 25 d and then gradually declined with age. Responses to short-term changes in irradiance after canopy closure indicated the stand light compensation point for photosynthesis to be near 200 micromoles m-2 s-1 PPFD. Tests in which CO2 concentration was raised to approximately 2000 micromoles mol-1 and then allowed to draw down to a compensation point showed that net photosynthesis was nearly saturated at > 1000 micromoles mol-1; below approximately 500 micromoles mol-1, net photosynthesis rates dropped sharply with decreasing CO2. The CO2 compensation point for photosynthesis occurred near 50 micromoles mol-1. Short-term (24 h) temperature tests showed net photosynthesis at 20 degrees C > or = 16 degrees C > 24 degrees C, while dark-period respiration at 24 degrees C > 20 degrees C > 16 degrees C. Rates of stand evapotranspiration peaked near Day 25 and remained relatively constant until about Day 75, after which rates declined slowly. Results from these tests will be used to model the use of plants for CO2 removal, O2 production, and water evaporation for controlled ecological life support systems proposed for extraterrestrial environments.
 
Article
Although terrestrial atmospheric CO2 levels will not reach 1000 micromoles mol-1 (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1(1%). Numerous studies have examined CO2 effects up to 1000 micromoles mol-1, but biochemical measurements indicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (approximately 1200 micromoles mol-1) and super-optimal CO2 levels (2400 micromoles mol-1) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub-optimal to near-optimal (350-1200 micromoles mol-1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 micromoles mol-1 reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-Apogee. Super-optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels from half to full sunlight. Subsequent trials revealed that super-optimal CO2 during the interval between 2 wk before and after anthesis mimicked the effect of constant super-optimal CO2. Furthermore, near-optimal CO2 during the same interval mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results suggest that super-optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.
 
Top-cited authors
Weikai Yan
Mark E Sorrells
  • Cornell University
Jose Crossa
  • Consultative Group on International Agricultural Research
Bingru Huang
  • Rutgers, The State University of New Jersey
Jean-Luc Jannink
  • United States Department of Agriculture