Showing papers in "Crop Science in 2007"

GGE Biplot vs. AMMI Analysis of Genotype-by-Environment Data

Abstract: The use of genotype main effect (G) plus genotype-by-environment (GE) interaction (G+GE) biplot analysis by plant breeders and other agricultural researchers has increased dramatically during the past 5 yr for analyzing multi-environment trial (MET) data. Recently, however, its legitimacy was questioned by a proponent of Additive Main Effect and Multiplicative Interaction (AMMI) analysis. The objectives of this review are: (i) to compare GGE biplot analysis and AMMI analysis on three aspects of genotype-by-environment data (GED) analysis, namely mega-environment analysis, genotype evaluation, and test-environment evaluation; (ii) to discuss whether G and GE should be combined or separated in these three aspects of GED analysis; and (iii) to discuss the role and importance of model diagnosis in biplot analysis of GED. Our main conclusions are: (i) both GGE biplot analysis and AMMI analysis combine rather than separate G and GE in mega-environment analysis and genotype evaluation, (ii) the GGE biplot is superior to the AMMI1 graph in mega-environment analysis and genotype evaluation because it explains more G+GE and has the inner-product property of the biplot, (iii) the discriminating power vs. representativeness view of the GGE biplot is effective in evaluating test environments, which is not possible in AMMI analysis, and (iv) model diagnosis for each dataset is useful, but accuracy gain from model diagnosis should not be overstated.

Prospects for genomewide selection for quantitative traits in maize

Abstract: The availability of cheap and abundant molecular markers in maize (Zea mays L.) has allowed breeders to ask how molecular markers may best be used to achieve breeding progress, without conditioning the question on how breeding has traditionally been done. Genomewide selection refers to marker-based selection without fi rst identifying a subset of markers with signifi - cant effects. Our objectives were to assess the response due to genomewide selection compared with marker-assisted recurrent selection (MARS) and to determine the extent to which phenotyping can be minimized and genotyping maximized in genomewide selection. We simulated genomewide selection by evaluating doubled haploids for testcross performance in Cycle 0, followed by two cycles of selection based on markers. Individuals were genotyped for NM markers, and breeding values associated with each of the NM markers were predicted and were all used in genomewide selection. We found that across different numbers of quantitative trait loci (20, 40, and 100) and levels of heritability, the response to genomewide selection was 18 to 43% larger than the response to MARS. Responses to selection were maintained when the number of doubled haploids phenotyped and genotyped in Cycle 0 was reduced and the number of plants genotyped in Cycles 1 and 2 was increased. Such schemes that minimize phenotyping and maximize genotyping would be feasible only if the cost per marker data point is reduced to about 2 cents. The convenient but incorrect assumption of equal marker variances led to only a minimal loss in the response to genomewide selection. We conclude that genomewide selection, as a brute-force and black-box procedure that exploits cheap and abundant molecular markers, is superior to MARS in maize.

HarvestPlus: Breeding Crops for Better Nutrition

Abstract: Micronutrient malnutrition, the so-calied hidden hunger, affects more than one-half of the world's population, especially women and preschool children in developing countries. Despite past progress in controlling micronutrient decencies through supplementation and food fortification, new approaches are needed to expand the reach of food-based interventions. Biofortification a new approach that relies on conventional plant breeding and modern biotechnology to increase the micronutrient density of staple crops, holds great promis for improving the nutritional status and health of poor populations in both rural and urban areas of the developing world. HarvestPlus, a research program implemented with the international research institutes of the CGIAR, targets a multitude of crops that are a regular part of the slaple-based diets of the por and breeds them to be rich in iron, zinc, and provitamin A. This paper emphasizes the need for interdisciplinary research and addresses the key research issues and methodological considerations for success. The major activities to be undertaken are broadly grouped into research related to nutrition research and impact analysis, and research considerations for delivering biofortified crops to end-users effectively. The paper places particular emphasis on the activities of the plant breeding and genetics component of this multidisciplinary program. The authors argue that for biofortification to succeed, product profiles developed by plant breeders must be driven by nutrition research and impact objectives and that nutrition research must understand that the probability of success for biofortified crops increases substantially when product concepts consider farmer adoption and, hence, agronomic superiority.

A large-effect QTL for grain yield under reproductive-stage drought stress in upland rice.

Abstract: Genetic control of yield under reproductive-stage drought stress was studied in a population of 436 random F 3 -derived lines from a cross between the upland rice (Oryza sativa L.) cultivars Vandana and Way Rarem. Screening was conducted under upland conditions at IRRI during the dry seasons of 2005 and 2006. Lines were evaluated in drought stress and nonstress trials in both years to identify QTL contributing to drought resistance. For QTL detection, a set of random lines and the highest and lowest-yielding lines under both stress and nonstress conditions were genotyped by 126 SSR markers. A QTL (qtl12.1) with a large effect on grain yield under stress was detected on Chromosome 12 in both years. The whole population was genotyped for additional markers on Chromosome 12, allowing QTL localization to a 10.2 cM region between SSR markers RM28048 and RM511. Under stress conditions, the locus also increased harvest index, biomass yield, and plant height while reducing the number of days to flowering. Under nonstress conditions, qtl12.1 did not significantly affect any trait. The additive effect of this QTL on grain yield under stress was 172 kg ha-1 per year over the 2 yr of testing, representing 47% of the average yield under stress and explaining 51% of the genetic variance. The yield-increasing allele was derived from the susceptible parent, Way Rarem, suggesting an epistatic effect. This is the first QTL reported in rice having a large and repeatable effect on grain yield under severe drought stress in the field.

Molecular Markers in a Commercial Breeding Program

Abstract: In the 1980s, DNA-based molecular markers were identified as having the potential to enhance corn (Zea mays L.) breeding. Research has demonstrated the advantage of using molecular markers for selection of simply inherited traits, however only a few studies have evaluated the potential to enhance genetic gain for quantitative traits. In the late 1990s, Monsanto decided to implement marker assisted selection for quantitative traits in our global plant breeding programs. We built genotyping systems and information tools and developed marker assisted methodologies that increased the mean performance in elite breeding populations.

Response to Direct Selection for Grain Yield under Drought Stress in Rice

Abstract: Drought is a major cause of yield loss in rain-fed rice (Oryza sativa L.), grown on over 40 million ha in Asia. The objective of this study was to evaluate the effectiveness of direct selection for yield under drought stress in upland rice in populations derived from crosses between irrigated high-yielding cultivars and upland-adapted cultivars. Random F 2:4 lines from five populations were screened for grain yield in fully irrigated lowland fields under nonstress conditions and in uplands under severe reproductive-stage drought stress. Stress caused mean yield reduction of 64% across populations. Broad-sense heritability for yield was not consistently lower in stress than in nonstress trials. Response to selection was evaluated in two crosses in subsequent seasons. Stress-selected lines had a yield advantage of 25 to 34% over random lines when evaluated at stress levels similar to those in which they were selected. Yield gains under very severe stress occurred only in a population derived from a highly tolerant parent. Direct selection usually gave greater response under stress than indirect selection under nonstress conditions. Direct selection under dry-season stress also gave response under naturally occurring wet-season stress. These results support the hypothesis that selection for yield under reproductive-stage drought stress is effective in rice, and that choice of donor is very important in breeding drought-tolerant rice.

Physiological Basis of Successful Breeding Strategies for Maize Grain Yield

Abstract: During the maize (Zea mays L.) hybrid era (1939 to present), commercial grain yields have improved neady sixfold and the genetic component of the improvement has been estimated as approximately 60%. In this paper, we examine physiological factors and successful breeding strategies that underlie the yield improvement. Grain yield is the product of accumulating dry matter and allocating a portion of the total dry matter to the grain. The processes influencing dry matter accumulation are commonly referred to as the "source" components, while the processes influencing allocation of dry matter to the grain are referred to as the "sink" components. On the source side, changes in leaf canopy size and architecture account for only a minor portion of the improvement. The majority of the improvement in source capacity is due to visual and functional "stay-green." On the sink side, the improvement is through changes in the relationship between kernel number per plant and plant growth rate during a period bracketing silking. In a breeding context, these improvements have been made (i) in a "closed" gemplasm pool stratified into heterotic groups; (ii) through use of a pedigree method of breeding structured to mimic reciprocal recurrent selection and thereby improving both additive and nonadditive genetic effects; and (iii) by a gradual increase in plant population densities during the hybrid era as the constant source of stress during both inbred line development and hybrid commercialization. Functional stay-green and the sink establishment dynamics still represent opportunities for yield improvements. It is essential that source and sink are kept in balance, and that improvement in one accompanies a simultaneous improvement in the other. One strategy for exploiting these opportunities is to incorporate high plant population density trials into inbred line development programs.

Genetic Improvement of Grain Yield and Associated Traits in the Northern China Winter Wheat Region from 1960 to 2000

Abstract: To understand the genetic gains of grain yield in the Southern China Winter Wheat Region (SCWWR), two yield potential trials, i.e., YPT 1 including 11 leading cultivars from the Middle and Low Yangtze Valley (Zone III) and YPT 2 including 15 leading cultivars from the Southwestern China Region (Zone IV) from 1949 to 2000, were conduced during the 2001–2003 cropping seasons. A completely randomized block design of three replicates was employed with controlled field environments. Molecular markers were used to detect the presence of dwarfing genes and the 1B/1R translocation. Results showed that average annual genetic gain was 0.31% (P < 0.05) or 13.96 kg/ha/year and 0.74% (P < 0.01) or 40.80 kg/ha/year in Zones III and IV, respectively. In YPT 1, changes of all other traits were not significant, but plant height was significantly reduced. In YPT 2, the genetic improvement of grain yield was primarily attributed to the increased thousand kernel weight (TKW) (0.65%, P < 0.01) and kernel weight/spike (0.87%, P < 0.01), reduced plant height and increased harvest index (HI). The dwarfing gene Rht 8 was most frequently present (46.1%), Rht-B1b was observed in three genotypes in Zone III, and Rht-D1b was present in only one genotype in Zone IV. The 1B/1R translocation was present in four genotypes. Utilization of Italian germplasm and development of landmark cultivar Fan 7 were the key factors for grain yield improvement in SCWWR. The future challenge of wheat breeding in this region is to continue improving grain yield and disease resistance, and to develop cultivars suitable for the reduced tillage of wheat/rice double cropping. Utilization of Mexican germplasm could provide opportunities for future yield improvement.

Correlation between Heat Stability of Thylakoid Membranes and Loss of Chlorophyll in Winter Wheat under Heat Stress

Abstract: Determining mechanisms associated with heat tolerance and identifying screening methods are vital for improvement of heat tolerance in plants. The objectives of this study were to investigate the relationship between the heat stability of thylakoids and loss of chlorophyll in winter wheat (Triticum aestivum L.) under heat stress, and to examine whether chlorophyll loss can be used as an indicator of heat tolerance in wheat. We assessed heat tolerance and measured chlorophyll content in 12 cultivars of winter wheat at fl owering stage during exposure to 16-d-long heat stress. Heat tolerance was assessed using fl uorescence to determine the heat stability of thylakoids, and chlorophyll content was measured with a chlorophyll meter. Experiments were conducted under controlled conditions. Heat stress caused damage to thylakoids in all cultivars as indicated by the increase in the ratio of constant fl uorescence (O) and the peak of variable fl uorescence (P). Heat stress also caused a decline in chlorophyll content in most cultivars. A strong negative correlation between heat-induced increases in O/P and chlorophyll content was seen. The results suggest that heat-induced damage to thylakoids and chlorophyll loss are closely associated in winter wheat. Measurements of chlorophyll content with a chlorophyll meter could be useful for high throughput screening for heat tolerance in wheat.

A modified colorimetric method for phytic acid analysis in soybean

Abstract: A quantitative, reproducible, and efficient phytic acid assay procedure is needed to screen breeding populations and support genetic studies in soybeans [Glycine max (L.) Merr.]. The objective of this study was to modify the colorimetric Wade reagent method and compare the accuracy and applicability of this new method in determining seed phytic acid content in soybean with three well-established phytic acid assay methods: anion exchange column (AEC), high-performance liquid chromatography (HPLC), and 31 P nuclear magnetic resonance (NMR). The CV for repeated measurements of a low phytic acid soybean mutant, CX1834-1-6, ranged from 1.8 to 4.2% (n = 5), indicating the results were precise and reproducible. Phytic acid content of 42 soybean genotypes as determined by this method showed a correlation of 93.7 to 96.6% with the measurements by AEC, HPLC, and NMR. According to analysis of covariance, using inorganic P content as a predictor, phytic acid P content in a given sample analyzed by the four assay methods can be estimated with four linear regression models at the α = 0.01 level. Compared with HPLC, AEC, and 31 P NMR, this modified colorimetric method is simpler and less expensive for assaying a large number of samples, allowing its effective application in breeding and genetic studies of low phytic acid soybean.

Growth, Gas Exchange, Chlorophyll Fluorescence, and Ion Content of Naked Oat in Response to Salinity

Abstract: Understanding of the physiological responses of crop plants to salinity stress is of paramount importance for selection of genotypes with improved tolerance to salt stress. Two naked oat (Avena sativa L.) genotypes, 'VAO-7' and 'VAO-24', were subjected to different salt concentrations (0, 50, 100, 150, 200, and 250 mM NaCI) to determine the effects of salt levels and stress duration on seedling growth, ion content, and photosynthetic productivity. Relative growth rate (RGR) and leaf chlorophyll were determined at weekly intervals after salinity was imposed. Total leaf area, plant dry weight, photosynthetic parameters, and plant tissue ion concentrations were determined at 25 d after salinity application. Under salt stress conditions, germination rates varied greatly among the genotypes. The differences between VAO-7 and VAO-24 for most parameters measured were significant after 2 wk of stress introduction at 200 and 250 mM NaCl. Salt stress at the lowest level (50 mM) reduced total leaf area by 35% and plant dry matter by 52%. At 25 d after salt stress, plants treated with the 250 mM NaCl accumulated 36-fold more Na + , 79% more Ca 2+ , and 2.4-fold less K + than the control. Salt treatment resulted in the reduction of almost all the growth parameters and coincident increases in plant Na + and Ca 2+ concentrations. Our results indicate that there is great variability for salt tolerance among naked oat germplasms, and greater photosynthesis capacity, higher RGR, and relatively lower tissue Na + accumulation at high salt concentrations appeared to be associated with salt tolerance in naked oats.

Biofuels in Brazil: an overview.

Abstract: The demand for food, fuel, and energy resources continues to increase worldwide. Currently, there are many international efforts aimed at finding renewable, sustainable, and environment friendly solutions for these problems. The spiraling price of petroleum and the adverse effects of using nonrenewable resources are major reasons for increased interest in renewable sources of energy. Brazil, the fifth largest and fifth most populated country in the world, has been developing successful initiatives in renewable sources of energy for more than 75 yr. The production and use of ethanol from sugarcane (Saccharum L.) is a global model for ethanol production, distribution, and use; therefore, the Brazilian ethanol industry has attracted interest from scientists, producers, and governments of both developed and developing countries. Like ethanol, biodiesel is also receiving increased interest in Brazil, with the source material for biodiesel production varying widely between regions. Several oleaginous species have been used, and others are being investigated as potential sources for biodiesel production. Biodiesel was introduced much later than ethanol in Brazil with the formation of the Brazilian Energy Matrix in January 2005 and a mandatory use of at least 2% (B2) biodiesel by 2008 and 5% (B5) by 2013. This paper presents a view of the historic development of ethanol and biodiesel programs in Brazil, emphasizing the strategic role of plant genetic resources as a pillar to support future improvements through plant breeding.

Molecular Breeding to Enhance Ethanol Production from Corn and Sorghum Stover

Abstract: Political and environmental concerns have resulted in a growing interest in renewable energy, escpeially transportation fuels. In the United States the majority of fuel ethanol is currently produced from corn (Zea mays L.) starch, but grain supplies will be insufficient to meet anticipated demands. Enzymatic hydrolysis of lignocellulosic biomass such as corn and sorghum [Sorghum bicolor (L.) Moench] stover can provide an abundant alternative source of fermentable sugars. While production of cellulosic ethanol from stover is feasible from an energy-balance perspective, its production is currently non economically competitive. Along with improvements in bioprocessing, enhancing the yield and composition of the biomass has the potential to make ethanol production considerably more cost effective. This requires (i) a better understanding of how cell wall composition and structure affect the efficiency of enzymatic hydrolysis, (ii) the development of traits that enhance biomass conversion efficiency and increase biomass yield, and (iii) the development of rapid screening protocols to evaluate biomass conversion efficiency. Several genetic resources are available to improve maize and sorghum as sources of lignocellulosic biomass. This includes the use of existing mutants, forward and reverse genetics to obtain novel mutants, and transgenic approaches in which the expression of genes of interest is modified. Plant breeding can be implemented to improve biomass yield, biomass quality, and biomass conversion efficiency, either through selection among progeny obtained by crossing parents with desirables traits, or as a way to enhance the agronomic performance of promisig mutants and transgenics. Examples from currents research will be used to illustrate progress in these different areas.

Validating the Fhb1 QTL for fusarium head blight resistance in near-isogenic wheat lines developed from breeding populations

Abstract: Quantitative trait loci (QTLs) have been identified for numerous species since the 1990s using populations developed from biparental crosses. The most common methods of validating QTLs are to quantify their effects in additional mapping populations or test near-isogenic lines (NILs) developed from the original mapping population. These approaches to QTL validation fail to adequately examine the effectiveness of a QTL in breeders' populations. We have developed an alternative QTL validation method in which NILs are developed from existing breeding populations segregating for the QTL. Our objective was to validate this method using Fhbl, a major Fusarium head blight [FHB; causal agent Fusarium graminearum (Schwabe)] resistance QTL in wheat (Triticum aestivum L.). Microsatellite markers flanking the QTL region were used to develop 19 QTL-NIL pairs by sampling F 3:4 families from 13 different populations. Each pair was tested in a greenhouse point-inoculation experiment and four field FHB resistance screening nurseries. Near-isogenic lines with the Fhbl resistance allele had significant (P < 0.001) average reductions of 23% for disease severity ratings and 27% for infected kernels in harvested grain. Disease spread for 9 out of 19 total pairs was significantly (P < 0.05) lower in greenhouse point-inoculation experiments when the Fhbl resistance allele was present. The QTL validation methodology employed in this study should be broadly applicable to other quantitative traits and plant species.

Evaluating potential genetic gains in wheat associated with stress-adaptive trait expression in elite genetic resources under drought and heat stress

Abstract: While genetic resources provide an invaluable gene pool for crop breeding, the majority of accessions in germplasm collections remain uncharacterized and their potential to improve stress adaptation is not quantified. A selection of 25 elite genetic resources for wheat (Triticum aestivum L.) were characterized for agronomic and physiological trait expression in drought- and heat-stessed environments. Under drought, the physiological traits best associated with yield were canopy temperature, associated with water uptake, und carbon isotope discrimination, associated with transpiration efficiency. Under heat stress stomatal conductance, leaf chlorophyll content, and canopy temperature (associated with radiation use efficiency in this environment) were well correlated with yield. Theoretical yield gains based on extrapolating the best trait expression to the highest yielding backgrounds were also estimated. Under drought, the best expression of canopy temperature and carbon isotope discrimination suggested petential yield gains of approximately 10 and 9% above the best yielding cultivars, respectively; under heat stress, canopy temperature and remobilization of stem carbohydrates suggested potential yield gains of approximately 7 and 9%, respectively. Other physiological trait expression was associated with potential yield gains to varying degrees. When considering agronomic traits, the best expression of harvest index suggested yield gains of approximately 14 and 24% in drought and hot environments, respectively, while the combined best expression of both harvest index and final aboveground biomass suggested yield gains of 30 and 34%, respectively. Principal component analysis indicated that mass were not strongly associated with each other, suggesting potential cumulative gene action for yield if traits were combined. When comparing trait expression across drought and hot environments, several physiological traits (e.g., canopy temperature) showed closer association with each other than did performance traits, supporting the idea that such stress-adaptive traits have genetic value across stresses.

Latitudinal and Longitudinal Adaptation of Switchgrass Populations

Abstract: Switchgrass (Panicum virgatum L.) is a warm- season native grass, used for livestock feed, bioenergy, soil and wildlife conservation, and prairie restoration in a large portion of the USA. The objective of this research was to quantify the relative importance of latitude and longitude for adaptation and agronomic performance of a diverse group of switchgrass populations. Six populations, chosen to represent remnant prai- rie populations on two north-south transects, were evaluated for agronomic traits at 12 loca- tions ranging from 36 to 47°N latitude and 88 to 101°W longitude. Although the population × location interactions accounted for only 10 to 31% of the variance among population means, many signifi cant changes in ranking and adap- tive responses were observed. Ground cover was greater for northern-origin populations evaluated in hardiness zones 3 and 4 and for southern-origin populations evaluated in har- diness zones 5 and 6. There were no adaptive responses related to longitude (ecoregion). Switchgrass populations for use in biomass production, conservation, or restoration should not be moved more than one hardiness zone north or south from their origin, but some can be moved east or west of their original ecore- gion, if results from fi eld tests support broad longitudinal adaptation.

Evaluation of Genetic Diversity and Genome‐wide Linkage Disequilibrium among U.S. Wheat (Triticum aestivum L.) Germplasm Representing Different Market Classes

Abstract: Genetic diversity and genome-wide linkage disequilibrium (LD) were investigated among 43 U.S. wheat (Triticum aestivum L.) elite cultivars and breeding lines representing seven U.S. wheat market classes using 242 wheat genomic simple sequence repeat (SSR) markers distributed throughout the wheat genome. Genetic diversity among these lines was examined using genetic distance-based and model-based clustering methods, and analysis of molecular variance. Four populations were identified from the model-based analysis, which partitioned each of the spring and winter populations into two subpopulations, corresponding largely to major geographic regions of wheat production in the United States. This suggests that the genetic diversity existing among these U.S. wheat germplasm was influenced more by regional adaptation than by market class, and that the individuals clustered in the same model-based population likely shared related ancestral lines in their breeding history. For this germplasm collection, genome-wide LD estimates were generally less than 1 cM for the genetically linked loci pairs. This may result from the population stratification and small sample size that reduced statistical power. Most of the LD regions observed were between loci less than 10 cM apart. However, the distribution of LD was not uniform based on linkage distance and was independent of marker density. Consequently, LD is likely to vary widely among wheat populations. © Crop Science Society of America.

Effects of a Biostimulant on the Heat Tolerance Associated with Photosynthetic Capacity, Membrane Thermostability, and Polyphenol Production of Perennial Ryegrass

Abstract: Limited research has been published to determine the impact of amino acid based biostimulants on turfgrass stress physiology and metabolism. Physiological responses of perennial ryegrass (Lolium perenne L.) treated with or without Macro-Sorb Foliar (FOLIAR) and subjected to optimal growing conditions or high air temperature stress (20, 28, and 36°C) were investigated in vivo using three separate growth chamber experiments. Turfgrass photochemical efficiency (Fv/Fm ratio), leaf membrane thermostability, and leaf antioxidant (polyphenol) concentration were measured. Perennial ryegrass treated with 0.64 mL m-2 FOLIAR and exposed to prolonged high air temperature stress (36°C) exhibited 95% better mean photochemical efficiency and 65% better membrane thermostability than control plants. Leaf polyphenol concentrations were largely unaffected by individual treatments or temperature. No treatment differences were detected for plants maintained in the optimal temperature regime (20°C), and only photochemical efficiency treatment difference were found for plants maintained at 28°C. The results show that exogenous and sequential applications of FOLIAR improved perennial ryegrass metabolic responses in a highly controlled growth chamber environment. It remains difficult to extrapolate data obtained from growth chamber experiments to the field; therefore, caution must be taken when making turfgrass management recommendations.

Breeding for Striga Resistance in Sorghum: Exploitation of an Intricate Host–Parasite Biology

Abstract: The parasitic weed Striga Lour. has been one of the more intractable agricultural problems seriously limiting productivity of cereal and legume crops in sub-Saharan Africa. The development of crop plants with resistance to Striga has been limited because of the complexity of interactions between host, parasite, and the physical environment. We formulated a novel approach based on developing and exploiting a thorough understanding of the biology of this intricate association. We employed this knowledge-based approach to develop powerful selection assays, to conduct genetic analyses, and to characterize the range of mechanism involved in host plant resistance to Striga. Information thus generated has been used to identify unique sources of resistance to Striga, introgress these genes into selected cultivars, and deploy sorghum [Sorghum bicolor (L.) Moench] cultivars with known sources of Striga resistance either independently or in tandem as genotypes with multiple mechanisms of resistance. High yielding sorghum cultivars with Striga resistance and evident grain quality characteristics have been developed and deployed in a number of African countries to be used as cultivars per se or as a central component of an integrated Striga management program.

Pollen-Based Screening of Soybean Genotypes for High Temperatures

Abstract: Soybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures . 35C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50 Ca t 5C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 mm). Mean cardinal temperatures (Tmin ,T opt, and Tmax) were 13.2, 30.2, and 47.2C for PG and 12.1, 36.1, and 47.0C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum (Tmax), minimum (Tmin), and optimum (Topt) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat-tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30C) compared with heat-intermediate (PI 471938) and heat-sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumellae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88-5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [CO2] did not modify reproductive parameters or CTRI. The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature-tolerant genotypes and temperature-dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.

The accuracy of varietal selection using factor analytic models for multi-environment plant breeding trials

Abstract: Modeling of cultivar x trial effects for multienvironment trials (METs) within a mixed model framework is now common practice in many plant breeding programs The factor analytic (FA) model is a parsimonious form used to approximate the fully unstructured form of the genetic variance-covariance matrix in the model for MET data In this study, we demonstrate that the FA model is generally the model of best fit across a range of data sets taken from early generation trials in a breeding program In addition, we demonstrate the superiority of the FA model in achieving the most common aim of METs, namely the selection of superior genotypes Selection is achieved using best linear unbiased predictions (BLUPs) of cultivar effects at each environment, considered either individually or as a weighted average across environments In practice, empirical BLUPs (E-BLUPs) of cultivar effects must be used instead of BLUPs since variance parameters in the model must be estimated rather than assumed known While the optimal properties of minimum mean squared error of prediction (MSEP) and maximum correlation between true and predicted effects possessed by BLUPs do not hold for E-BLUPs, a simulation study shows that E-BLUPs perform well in terms of MSEP

Genotypic Variation for Three Physiological Traits Affecting Drought Tolerance in Soybean

Abstract: Three physiological traits that may affect performance of soybean [Glycine max (L.) Merr.] when soil water availability is limiting are (i) water use efficiency (WUE), (ii) regulation of whole plant water use in response to soil water content, and (iii) leaf epidermal conductance (ge) when stomata are closed. Six soybean plant introductions (PIs), eight breeding lines derived from them, and nine cultivars were compared for variability in these three traits during vegetative growth in two greenhouse studies. In the first experiment, whole plant water use, normalized both to plant size and evaporative demand (the normalized transpiration ratio, NTR), was monitored during a 10-d cycle of gradually increasing drought stress and then for an additional 2 d following rewatering. The critical soil water content at which each plant began to reduce its water use (FTSWC), was determined. The WUE was estimated as the ratio of total plant dry weight to total water used. In the second experiment, ge was determined for these same 23 genotypes by measuring leaf water vapor exchange after a 36-h dark adaptation. Substantial variation was found among genotypes for WUE, FTSWC, ge, and also the extent to which NTR recovered on rewatering. Generally, adapted cultivars had greater WUE and lower ge than did PIs. However, PI 471938 and its progeny N98-7264 were clear exceptions to this trend. An unexpected finding was that WUE was significantly negatively correlated with ge across genotypes.

Nitrogen uptake and utilization in contrasting nitrogen efficient tropical maize hybrids

Abstract: Maize cultivars with improved grain yields under nitrogen (N) stress are desirable for sub-Saharan African maize growing environments. This study assesses N uptake, N utilization, and the genotype x environment (G x E) interaction of 16 tropical maize (Zea mays L.) hybrids differing in grain yield under low-N conditions. Hybrids were evaluated under low-N, medium-N, and high-N at Harare, Zimbabwe, in 2003 and 2004 and at Kiboko, Kenya, in 2003. At maturity, N accumulation in the aboveground biomass ranged from 47 to 278 kg N ha -1 in various experiments. Grain yields ranged from 1.5 to 4.3 Mg ha -1 and 10.6 to 14.9 Mg ha -1 for the same experiments, respectively. Significant G x E interactions were observed which became more pronounced as the difference in N stress intensity between two environments increased. High grain yield under low-N was consistently associated with higher postanthesis N uptake, increased grain production per unit N accumulated, and an improved N harvest index. Additive main effect and multiplicative interaction analysis identified hybrids with specific adaptation to either low-N or high-N environments. Several hybrids produced high yields under both low-N and high-N conditions. More detailed studies with these hybrids are required to examine the underlying physiological mechanisms contributing to the N-use efficiency.

Maize Biomass Yield and Composition for Biofuels

Abstract: With the world oil reserves projected to be depleted in about 40 years at the current pace of use, emphasis has shifted to alternative sources of liquid fuel. Currently, ethanol produced from approximately 20% of corn (Zea mays L.) grain in the United States contributes approximately 3.5% of the volume and 2.5% of the energy equivalent of annual gasoline consumption. Cellulosic biomass has the potential to contribute substantially to the biofuels pool. Corn is the single-largest source of crop residue in the United States. An unaltered cell wall is recalcitrant to hydrolytic enzymes required for the conversion of its polysaccharide fraction into simple sugars before fermentation. Attempts at lowering lignin to increase stover digestibility are generally accompanied by a reduction in biomass. The complexity of the cellulose synthase system poses a challenge in increasing its activity through biotechnological means. Exploitation of natural variation may thus be a more productive route to increase the stover cellulose content. In comparison, the objective of reducing or altering hemicellulose for improved ethanol production as well as digestibility of the grain by monogastric animals may be relatively easier to accomplish through transgenic means. Availability of molecular tools for many of the steps in cell wall biosynthesis and modification has opened the heretofore inaccessible biotechnological avenues to alter the wall composition and perhaps structure for increased ethanol production.

Map Location of the Rpp1 Locus That Confers Resistance to Soybean Rust in Soybean

Abstract: Soybean rust (SBR), caused by Phakopsora pachyrhizi, was fi rst discovered in North America in 2004 and has the potential to become a major soybean [Glycine max (L.) Merr.] disease in the USA. Currently, four SBR resistance genes have been identifi ed but not mapped on the soybean genetic linkage map. One of these resistance genes is the Rpp1 gene, which is present in the soybean accession PI 200492. The availability of molecular markers associated with Rpp1 will permit marker-assisted selection and expedite the incorporation of this gene into U.S. cultivars. We compared simple sequence repeat (SSR) markers between ‘Williams 82’ and the BC 5 Williams 82 isoline L85-2378, which contains the Rpp1 resistance allele from the soybean accession PI 200492, for candidate regions that might contain Rpp1. One candidate region was found with the SSR marker BARC_Sct_187 on linkage group G. A population of BC 6 F 2:3 lines segregating for the Rpp1 resistance locus was genotyped in this region on linkage group G followed by inoculation with the P. pachyrhizi isolate India 73-1 in the USDA-ARS Biosafety Level 3 Plant Pathogen Containment Facility at Ft. Detrick, MD. The Rpp1 gene was mapped between SSR markers BARC_Sct_187 and BARC_Sat_064 on linkage group G.

Breeding for Modified Fatty Acid Composition in Soybean

Abstract: Genetic modification of the fatty acid composition of soy bean [Glycine max (L.) Merr.] oil has been successful in better meeting the needs of end users than is possible with conventional oil. Three modified oils are or have been sold commercially. Oil in which the linolenic acid (18:3) content has been reduced from 8 to 1% makes it possible to reduce or eliminate the need for chemical hydrogenation to achieved. the stability and shelf life necessary for some food applications. Elimination of chemical hydrogenation and the trans fatty acids produced by the process is important for human health. Oil in which the acid (18:1) has been increased from 25 to > 80% also have increased its stability and shell life. An oil with palmitic acid (16.0) reduced from 11 to <4% makes impossible to achieve a low content of saturated fatty acids which is desirable for cardiovascular health. The genetic changes in soybean oil were achieved by conventional breeding and genetic engineering. Mutagenesis was the conventional breeding method used to develop the major genes for reduced palmitic and linolenic acids that are in the cultivars currently grown for commercial production. Genetic engineering was used to elevate oleic acid to <80%. The purpose of this paper modifications, the inheritance of the modifications, the impact of the trait on agronomic and seed characteristics, the methods of phenotypic and genotypic selection, and the commercial status of the modified oils.

Prebreeding in Common Bean and Use of Genetic Diversity from Wild Germplasm

Abstract: Common bean (Phaseolus vulgaris t.) is the most widely consumed grain legume in the world. This cultigen was domesticated from wild P. vulgaris, an indeterminate viny plant, distributed from Mexico to Argentina in midaltitude neotropical and subtropical regions. To colgnize such diverse ecological niches, the species possesses many adaptation traits and a wealth of genetic diversity,.However, breeding programs are limited by the under-utilization of the available genetic diversity because of the necessity of prebreeding exotic material.Due to partial reproductive isolation between the domesticated Andean and Mesoamerican gene pools, hybridations between wild and domesticated types of P.vulgaris from the sam gene pool offer greater potential to enhance the variation in the crop. Evaluations of wid P. vulgaris accessions have shown resistance to insects and diseases and higher N, Fe, and Ca content in seeds, which will qltimately contribute to improvements in nutritional quality and yield. Recurrent and inbred backcross methods are being used for the transfer of bath qualitative and quantitative traits from wild into domesticated forms of P. vulgaris, specific data on yield and 100-seed weight are presented. The prebreeding efforts will be enhanced by (i) information on gene pool origins, domestication syndrome traits, molecular diversity, and mapping data of the wild forms; (ii) indirect screening for biotic and abiotic stresses and (iii) marker-assisted selection.

Nutrient Cycling in Warm-Climate Grasslands

Abstract: Nutrients cycle among pools within an ecosystem, and losses of nutrients to the environment accompany each transfer from pool to pool. Efficient recapture of nutrients by plants is critical in extensively managed grasslands if these swards are to persist. In intensively managed systems, the greatest contribution of efficient recapture of nutrients may be minimizing loss of nutrients to the environment and associated negative impacts. Regardless of management intensity, grassland management decisions should be informed by an understanding of the dynamics of nutrient cycling. A significant body of literature has emerged in recent years describing nutrient dynamics in warm-climate grasslands. In warm climates globally, grasslands are most often low-input production systems dominated by C 4 grasses. These characteristics affect nutrient cycling, resulting in very different management challenges and opportunities than in higher input, C 3 -grass or legume-dominated, grasslands. This paper will focus on warm-climate grasslands. Within that context its objectives are (i) to describe the most prominent pools of C, N, P, and K, (ii) to discuss fluxes among nutrient pools, with emphasis on plant litter and animal excreta, iii) to describe the importance, management, and dynamics of soil organic matter, and (iv) to review the impact of grazing systems on nutrient cycling.

The Value to Herbivores of Plant Physical and Chemical Diversity in Time and Space

Abstract: Whether foraging on pastures or rangelands, herbivores encounter plant species that differ in their concentrations of nutrients. They also all contain various secondary compounds that at too high doses can be toxic, but at the appropriate dose many of these toxins may have medicinal benefits. The quantity of forage an animal consumes depends on the other forages it selects because nutrients and toxins interact. Food intake also depends on an individual's morphology and physiology, and marked variation is common, even among closely related animals, in needs for nutrients and abilities to cope with toxins. Thus, individuals can better meet their needs when offered a variety of foods that differ in nutrients and toxins than when constrained to a single food. Nonetheless, we have focused on a few species, often grown in monoculture, and we have reduced concentrations of secondary compounds with little appreciation for their roles in protecting plants against herbivores, pathogens, and competitors. In nature, where diversity of plants is the rule and not the exception, eating a variety of foods is how animals cope with, and may benefit from, secondary compounds. The potential benefits of creating mixtures of plant species whose nutrient and secondary compound profiles complement one another are obvious, though much remains to be learned about how to reconstruct agro-ecosystems with plants that complement and enhance one another structurally, functionally, and biochemically.

Potential Use of Spectral Reflectance Indices as a Selection Tool for Grain Yield in Winter Wheat under Great Plains Conditions

Abstract: Selection criteria that would facilitate increased genetic gain for grain yield would be considered advantageous in plant breeding programs. We evaluated the potential of spectral reflectance indices (SRI) for assessing grain yield variability in winter wheat (Triticum aestivum L.) genotypes under Great Plains conditions. One experiment was conducted at two locations on the Oklahoma State University research farms for 1 yr, and two experiments were conducted for 2 yr at a single location. The first experiment included 25 winter wheat cultivars from the Great Plains, and the other two experiments contained two groups of 25 F 4:6 and F 4:7 recombinant inbred lines. Six reported SRI (red and green normalized difference vegetation index, RNDVI, GNDVI; simple ratio, SR; water index, WI; normalized water indices 1 and 2, NWI-1 and NWI-2), and two new normalized water indices (NWI-3 and NWI-4) were calculated at booting, heading, and early grain-filling stages using a FiefdSpec UV/VNIR spectroradiometer. Significant genotypic variation was observed for SRI and growth stages, though the booting stage was least associated with grain yield. The relationships of grain yield with WI and NWI were stronger than with the RNDVI and SR. The WI and the NWI performed better in identifying superior genotypes, either at any individual growth stage or in a combination of growth stages. Our study clearly demonstrated the potential of using SRI as a selection tool for grain yield in a winter wheat breeding program.