Showing papers in "Crop Science in 2009"

Genomic Selection for Crop Improvement

Abstract: Despite important strides in marker technologies, the use of marker-assisted selection has stagnated for the improvement of quantitative traits. Biparental mating designs for the detection of loci affecting these traits (quantitative trait loci [QTL]) impede their application, and the statistical methods used are ill-suited to the traits' polygenic nature. Genomic selection (GS) has been proposed to address these deficiencies. Genomic selection predicts the breeding values of lines in a population by analyzing their phenotypes and high-density marker scores. A key to the success of GS is that it incorporates all marker information in the prediction model, thereby avoiding biased marker effect estimates and capturing more of the variation due to small-effect QTL. In simulations, the correlation between true breeding value and the genomic estimated breeding value has reached levels of 0.85 even for polygenic low heritability traits. This level of accuracy is sufficient to consider selecting for agronomic performance using marker information alone. Such selection would substantially accelerate the breeding cycle, enhancing gains per unit time. It would dramatically change the role of phenotyping, which would then serve to update prediction models and no longer to select lines. While research to date shows the exceptional promise of GS, work remains to be done to validate it empirically and to incorporate it into breeding schemes.

Can Changes in Canopy and/or Root System Architecture Explain Historical Maize Yield Trends in the U.S. Corn Belt?

Abstract: Continuous increase in the yield of maize (Zea mays L.) in the U.S. Corn Belt has involved an interaction with plant density. A number of contributing traits and mechanisms have been suggested. In this study we used a modeling approach to examine whether changes in canopy and/or root system architecture might explain the observed trends. A maize crop model was generalized so that changes in canopy and root system architecture could be examined. A layered, diurnal canopy photosynthesis model was introduced to predict consequences of change in canopy architecture. A two-dimensional root exploration model was introduced to predict consequences of change in root system architecture. Field experiments were conducted to derive model parameters for the base hybrid (Pioneer 3394). Simulation studies for various canopy and root system architectures were undertaken for a range of sites, soils, and densities. Simulated responses to density compared well with those found in field experiments. The analysis indicated that (i) change in root system architecture and water capture had a direct effect on biomass accumulation and historical yield trends; and (ii) change in canopy architecture had little direct effect but likely had important indirect effects via leaf area retention and partitioning of carbohydrate to the ear. The study provided plausible explanations and identified testable hypotheses for future research and crop improvement effort.

Biplot Analysis of Genotype × Environment Interaction: Proceed with Caution

Abstract: Biplot analysis has been used for studying genotype × environment interaction (GE) or any two-way table. Its descriptive and visualization capabilities along with the availability of userfriendly software have enabled plant scientists to examine any two-way data by a click on a computer button. Despite widespread use, the validity and limitations of biplot analysis have not been completely examined. Here we identify and briefl y discuss six key issues surrounding overutilization or abuse of biplot analysis. We question (i) whether the retention of the fi rst two multiplicative terms in the biplot analyses is adequate; (ii) whether the biplot can be more than a simple descriptive technique; (iii) how realistic a “which-won-where” pattern is identifi ed from a biplot; (iv) what if genotypes and/ or environments are random effects; (v) how relevant biplot analysis is to the understanding of the nature and causes of interaction; and (vi) how much the biplot analysis can contribute to detection of crossover interaction. We stress the need for use of confi dence regions for individual genotype and environment scores in biplots to make critical decisions on genotype selection or cultivar recommendation based on a statistical test. We conclude that the biplot analysis is simply a visually descriptive statistical tool and researchers should proceed with caution if using biplot analysis beyond this simple function.

Ridge Regression and Extensions for Genomewide Selection in Maize

Abstract: This paper reviews properties of ridge regres- sion for genomewide (genomic) selection and establishes close relationships with other meth- ods to model genetic correlation among rela- tives, including use of a kinship matrix and the simple matching coeffi cient as computed from marker data. A number of alternative models are then proposed exploiting ties between genetic correlation based on marker data and geostatis- tical concepts. A simple method for automatic marker selection is proposed. The methods are exemplifi ed using a series of experiments with test-cross hybrids of maize (Zea mays L.) con- ducted in fi ve environments. Results underline the need to appropriately model genotype- environment interaction and to employ an inde- pendent estimate of error. It is also shown that accounting for genetic effects not captured by markers may be important.

An Alternate Wetting and Moderate Soil Drying Regime Improves Root and Shoot Growth in Rice

Abstract: A major challenge in rice (Oryza sativa L.) production is to achieve the dual goal of increasing food production and saving water. This study aimed to investigate if alternate wetting and drying regimes could improve root and shoot growth and consequently increase grain yield and water use efficiency (WUE). Two rice varieties were field-grown at Yangzhou, China in 2005 and 2006. Three irrigation regimes, alternate wetting and moderate soil drying (WMD, re-watered when soil water potential reached -15 kPa at 15-20 cm depth), alternate wetting and severe soil drying (WSD, re-watered when soil water potential reached -30 kPa), and a conventional irrigation (Cl, continuously flooded), were imposed during the whole growing season. Compared with the Cl, the WMD regime significantly increased, whereas the WSD regime reduced, root oxidation activity, cytokinin concentrations in roots and shoots, leaf photosynthetic rate, and activities of key enzymes involved in sucrose-to-starch conversion in grains. Grain yield of the two varieties, on the average, was increased by 11% under the WMD regime, and was reduced by 32% under the WSD regime when compared with that under the Cl regime. Averaged WUE of the two varieties was increased by 55% under the WMD regime and 36% under the WSD regime. We conclude that a moderate wetting and drying regime can enhance root growth which benefits other physiological processes and result in higher grain yield and WUE.

Meta-analysis of QTL associated with Fusarium head blight resistance in wheat.

Abstract: Quantitative trait loci (QTL) associated with resistance to Fusarium head blight (FHB), which is mainly caused by Fusarium graminearum Schwabe [telomorph: Gibberella zeae Schw. (Petch)], have been identified in wheat (Triticum aestivum L.) from different countries. Due to the differences of genetic backgrounds and analysis methods, the linked marker and significance levels of QTL are not consistent across studies. Such discrepancies make it difficult to select diagnostic flanking markers. Meta-analysis has been used to estimate the confidence intervals (Cls) of QTL in plant and animal genomes. The objective of this study was to cluster 249 FHB resistance QTL identified in 46 unique lines from 45 studies based on the estimated QTL Cl by meta-analysis. A total of 209 QTL conditioning FHB resistance type I, II, III and IV were classified into 43 clusters on 21 chromosomes. Among them, 119 QTL were significant and 116 QTL explained more than 10% of phenotypic variation. There are 19 confirmed QTL located on chromosomes 3A, 5A, 7A, 1 B, 3BS, 5B, 6B, and 2D. The results provide chromosome locations and linked markers for overlapping and unique QTL. Markers flanking QTL clusters can be used to pyramid diverse QTL more efficiently through marker-assisted breeding.

Impact of high nighttime temperature on respiration, membrane stability, antioxidant capacity, and yield of rice plants.

Abstract: Nighttime temperature is one of the major environmental factors infl uencing plant metabolic processes. The respiration rates, membrane thermal stability (MTS), and total antioxidant capacities of leaves were investigated in rice (Oryza sativa L.) plants when exposed to high nighttime temperature (HNT) (32°C) or ambient nighttime temperature (ANT) (27°C), and with or without potential preventive exogenous effector (chemical) treatments. The exogenous effector treatments included α-tocopherol (vitamin E), glycine betaine, and salicylic acid, which play important but different roles in inducing thermal tolerance in many plant species. Plants were subjected to an HNT through use of continuously controlled infrared heaters, starting from 2000 h until 0600 h. High nighttime temperature increased respiration rates, decreased MTS, and negatively affected the yield (by 95%). Application of salicylic acid somewhat lowered the reduction in yield due to HNT (76 vs. 95%) by decreasing the respiration rates and increasing MTS and total antioxidant capacity of rice plants.

Comparison of Weighting in Two-Stage Analysis of Plant Breeding Trials

Abstract: Series of plant breeding trials are often unbalanced and have a complex genetic structure. To reduce computing cost, it is common practice to employ a two-stage approach, where adjusted means per location are estimated and then a mixed model analysis of these adjusted means is performed. An important question is how means from the first step should be weighted in the second step. Our objective therefore was the comparison of different weighting methods in the analysis of four typical series of plant breeding trials using mixed models with fixed or random genetic effects. We used four published weighting methods and proposed three new methods. Four evaluation criteria were computed to compare methods, using one-stage analysis as benchmark. We found that the two-stage analysis gave acceptable results with fixed genetic effects. When genetic effects were taken as random in stage two, in three of four datasets the two-stage analysis gave acceptable results. In both cases differences between weighting methods were small and the best weighting method depended on the dataset but not on the evaluation criteria. A two-stage analysis without weighting also produced acceptable results, but weighting mostly performed better. In the fourth dataset the missing data pattern was informative, resulting in violation of the missing-at-random (MAR) assumption in one- and two-stage analysis. In this case both analyses were not strictly valid.

Developing a mini core collection of sorghum for diversified utilization of germplasm.

Abstract: The sorghum [Sorghum bicolor (L.) Moench] germplasm collection at the ICRISAT gene bank exceeds 37,000 accessions. A core collection of 2247 accessions was developed in 2001 to enable researchers to have access to a smaller set of germplasm. However, this core collection was found to be too large. To overcome this, a sorghum mini core (10% accessions of the core or 1% of the entire collection) was developed from the existing core collection. The core collection was evaluated for 11 qualitative and 10 quantitative traits in an augmented design using three control cultivars in the 2004–2005 postrainy season. The hierarchical cluster analysis of data using phenotypic distances resulted in 21 clusters. From each cluster, about 10% or a minimum of one accession was selected to form a mini core that comprised 242 accessions. The data in the mini core and core collections were compared using statistical parameters such as homogeneity of distribution for geographical origin, biological races, qualitative traits, means, variances, phenotypic diversity indices, and phenotypic correlations. These tests revealed that the mini core collection represented the core collection, which can be evaluated extensively for agronomic traits including resistance to biotic and abiotic stresses to identify accessions with desirable characteristics for use in crop improvement research and genomic studies. International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru PO, Hyderabad, Andhra Pradesh 502 324, India. Received 11 Jan. 2009. *Corresponding author (h.upadhyaya@cgiar.org). Abbreviations: CR%, coincidence rate; H`, diversity index; REML, residual maximum likelihood; VR%, variable rate.

Bulked Segregant Analysis Using the GoldenGate Assay to Locate the Rpp3 Locus that Confers Resistance to Soybean Rust in Soybean

Abstract: Few resistance loci to soybean rust (SBR), caused by Phakopsora pachyrhizi Syd., have been genetically mapped and linked to molecular markers that can be used for marker assisted selection. New technologies are available for single nucleotide polymorphism (SNP) genotyping that can be used to rapidly map traits controlled by single loci such as resistance to SBR. Our objective was to demonstrate that the highthroughput SNP genotyping method known as the GoldenGate assay can be used to perform bulked segregant analysis (BSA) to fi nd candidate regions to facilitate effi cient mapping of a dominant resistant locus to SBR designated Rpp3. We used a 1536 SNP GoldenGate assay to perform BSA followed by simple sequence repeat (SSR) mapping in an F 2 population segregating for SBR resistance conditioned by Rpp3. A 13-cM region on linkage group C2 was the only candidate region identifi ed with BSA. Subsequent F 2 mapping placed Rpp3 between SSR markers BARC_Satt460 and BARC_Sat_263 on linkage group C2 which is the same region identifi ed by BSA. These results suggest that the GoldenGate assay was successful at implementing BSA, making it a powerful tool to quickly map qualitative traits since the GoldenGate assay is capable of screening 1536 SNPs on 192 DNA samples in three days.

Effects of silicon and drought stress on tuber yield and leaf biochemical characteristics in potato.

Abstract: Sao Paulo State Univ, UNESP, Coll Agr Sci, Dep Crop Sci,Legeado Expt Farm, BR-18610307 Botucatu, SP, Brazil

Genome-Wide Reduction of Genetic Diversity in Wheat Breeding

Abstract: Public concerns about crop uniformity introduced by modern plant breeding and genetic vulnerability to biotic and abiotic stresses have been one of the major forces driving long-term efforts in plant germplasm conservation for future food security However, such concerns have gained little empirical support, as recent molecular diversity analyses of improved crop gene pools did not reveal much reduction from early to recent breeding efforts We conducted a genome-wide examination of 75 Canadian hard red spring wheat (Triticum aestivum L) cultivars released from 1845 to 2004 using 370 simple sequence repeat (or SSR) markers that were widely distributed over all 21 wheat chromosomes A total of 2280 SSR alleles were detected Allelic reduction occurred in every part of the wheat genome and a majority of the reduced alleles resided in only a few early cultivars Significant allelic reduction started in the 1930s Considering 2010 SSR alleles detected in the 20 earliest cultivars, 38% of them were retained, 18% were new, and 44% were lost in the 20 most recent cultivars The net reduction of the total SSR variation in 20 recent cultivars was 17% This clear-cut evidence not only supports the contention that modern plant breeding reduces the genetic diversity of Canadian wheat, but also underlies the need for conserving wheat germplasm and introducing genetic diversity into wheat breeding

QTL Analysis of Seed Iron, Zinc, and Phosphorus Levels in an Andean Bean Population

Abstract: Iron and zinc are essential micronutrients for human health often found in insuffi cient quantities in the diet. Biofortifi cation of seed crops has been undertaken to reduce micronutrient malnutrition. The objectives of this study were to identify variability for seed Fe, Zn, P, and phytic acid levels in an F 5:7 recombinant inbred line (RIL) population developed from a cross between AND696 and G19833, both common beans (Phaseolus vulgaris L.) of Andean origin. Quantitative trait loci (QTL) analysis was conducted with data from 2 yr and 2 P treatments with a previously described linkage map of AND696/ G19833. Signifi cant environmental and genetic variability for Fe, Zn, and P levels was identifi ed, and Fe and Zn levels were correlated (up to r = 0.53). Quantitative trait loci for seed Fe and Zn co-localized on three linkage groups (B1, B6, and B11). On B6, a QTL for Fe (R 2 = 0.36) was found at the same marker interval as a QTL for seed Zn (R 2 = 0.39), both derived from AND696. Quantitative trait loci for seed P were identifi ed on six linkage groups and explained 17 to 55% of the total phenotypic variation depending on year and environment.

Genetic Assessment of a Mini-Core Subset Developed from the USDA Rice Genebank

Abstract: Development of core collections is an effective tool to extensively characterize large germplasm collections, and the use of a mini-core subsampling strategy further increases the effectiveness of genetic diversity analysis at detailed phenotype and molecular levels. We report the formation of a mini-core subset containing 217 entries derived from 1794 core entries representing the genetic diversity found in more than 18,000 accessions of the USDA-ARS rice (Oryza sativa L.) germplasm collection. The mini-core was developed with PowerCore software on the basis of 26 phenotypic traits and 70 molecular markers. The 217 entries in the mini-core had a similar distribution over 15 geographical regions, with 1794 entries in the original core collection. The resultant mini-core had 6.3% of mean difference (MD%), 16.5% of variance difference (VD%), 102.7% of variable rate (VR%), and 97.5% of coincidence rate (CR%) with the core collection, which brought about full coverage of 26 traits. All 962 alleles identifi ed by the 70 markers in the core collection were captured in the mini-core, which maximized allelic richness up to 100% and resulted in an average genetic diversity (Nei index) of 0.76, ranging from 0.37 to 0.97 among the markers. In conclusion, the mini-core presented in this study is a highly suitable and representative subset of the USDA rice core collection as well as the entire USDA-ARS rice germplasm holdings. Univ. of Arkansas, Rice Research and Extension Center, 2900 Highway 130E, Stuttgart, AR 72160. Received 22 Sept. 2008. *Corresponding author (hagrama@uark.edu). Abbreviations: ASV, alkali spreading value; CR%, coincidence rate; MD%, mean diff erence; PCR, polymerase chain reaction; QTL, quantitative trait loci; SNP, single nucleotide polymorphism; SSR, simple sequence repeat; VD%, variance diff erence; VR%, variable rate.

Genomewide selection for rapid introgression of exotic germplasm in maize.

Abstract: The length of time needed for prebreeding in adapted x exotic maize (Zea mays L.) crosses has deterred breeders from exploiting exotic germplasm. My objective in this study was to determine, by simulation, the usefulness of genomewide selection for the rapid improvement of an adapted x exotic cross. I simulated F 2 , BC 1 , and BC 2 populations from an adapted x exotic maize cross. The adapted inbred had the favorable allele at L Adapted = 50 quantitative trait loci (QTL), whereas the exotic inbred had the favorable allele at L Exotic = 50, 25, 10, or 5 QTL. The joint effects of 512 markers were fitted by best linear unbiased prediction. For L Exotic ≤ 25, the maximum responses (in units of the testcross genetic standard deviation) to multiple cycles of genomewide selection ranged from 0.38 to 3.81. Responses increased as heritability increased and as the number of testcrosses that were phenotyped in Cycle 0 increased from 144 to 288. Overall, the results indicated that a useful strategy for the rapid improvement of an adapted x exotic cross involves 7 to 8 cycles of genomewide selection starting in the F 2 rather than in a backcross population, even when the number of favorable alleles is substantially larger in the adapted parent than in the exotic parent. Assuming three generations can be grown per year in a greenhouse or year-round nursery, this procedure would require only 3 yr beyond the time required to develop and phenotype the Cycle 0 testcrosses.

The Putative Mesoamerican Domestication Center of Phaseolus vulgaris Is Located in the Lerma–Santiago Basin of Mexico

Abstract: Mesoamerican food agriculture is defi ned by the milpa cropping system, consisting of maize (Zea mays L.), common bean (Phaseolus vulgaris L.), and squash (Cucurbita spp.). In recent years, a domestication center for maize has been proposed in the Balsas River basin in west-central Mexico, raising the question whether the Balsas basin was also the center of origin for Mesoamerican food agriculture in general. We conducted a survey of genetic diversity for 26 microsatellite markers in a representative sample of 155 wild and domesticated common bean from its Mesoamerican gene pool. Microsatellite diversity was analyzed with STRUCTURE, neighbor-joining tree construction, and principal coordinate analysis. Most Mesoamerican domesticated accessions clustered in a single group, suggesting a single domestication. Furthermore, the most closely related wild beans to the domesticated clade originated from a restricted region in the Rio Lerma–Rio Grande de Santiago basin in west-central Mexico, distinct from the Balsas basin. Although wild maize and Phaseolus beans grow together in the wild, they appear to have been domesticated in different regions to be reunited later on in a single cropping system. Crop domestications in Mesoamerica may therefore have a diffuse rather than a single geographic origin. Archaeological and ecological investigations into the origins of agriculture should be refocused from the arid eastern half of Mexico to the west-central part of the country.

Two alleles of ahFAD2B control the high oleic acid trait in cultivated peanut.

Abstract: A high oleic:linoleic acid ratio (O/L) in peanut (Arachis hypogaea L.) seeds is controlled primarily by two recessive genes, ahFAD2A and ahFAD2B (ol 1 and ol 2 ). Marker-assisted breeding for high O/L could become routine provided that userfriendly and economical markers could be developed that would target mutant alleles underlying the trait. Previously, a mutant allele of ahFAD2A was characterized as having a 448G>A transition, and two ahFAD2B alleles were found with either a nonsense mutation caused by a single nucleotide insertion (441_442insA) (high O/L line F435) or a transposable element insertion (Flavorunner 458). A cleaved amplifi ed polymorphic sequence (CAPS) marker targeting the 441_442insA site in ahFAD2B was designed. ‘Georgia-02C’ and ‘Georgia Hi-O/L’, derivatives of irradiation-induced high O/L mutants, showed CAPS marker and sequence data diagnostic for the genetic mutations in ahFAD2 found in the spontaneous mutant line F435. In addition, confl icting reports regarding the organization of ahFAD2 genes and ahFAD2B mutations were reexamined. Our data clearly show that molecular markers can be used to screen for known ahFAD2 mutations and that only two mutant ahFAD2B alleles are present in the U.S. high O/L cultivars. Genetic markers based on these mutations have utility for detecting seed mixtures and heterozygotes, and can accelerate introduction of the high O/L trait into peanut breeding lines. Y. Chu and P. Ozias-Akins, Dep. of Horticulture, Univ. of Georgia Tifton Campus, Tifton GA 31793; C.C. Holbrook, Research Geneticist, USDA-ARS, P.O. Box 748, Tifton, GA 31793. Funding was provided by the Georgia Seed Development Commission and the Univ. of Georgia Research Foundation Cultivar Development Program. Received 14

Genetic Variability of Seed Sugar Content in Worldwide Soybean Germplasm Collections

Abstract: Soluble sugar is an important quality trait in food-grade soybeans [Glycine max (L.) Merr.]. Desirable sugars such as sucrose, glucose, and fructose can help improve the taste and flavor of soyfood including tofu, soymilk, and natto; whereas oligosaccharides including raffinose and stachyose are indigestible by humans and animals and often cause flatulence or diarrhea. In this study, 241 plant introductions (PIs) of three maturity groups (MGs) from 28 origins were investigated for seed sugar content including glucose, fructose, sucrose, raffinose, and stachyose. Variation was detected in individual and total sugars in soybean PIs from different origins and MGs. Sucrose and stachyose are the major sugars in soybean seed. The sucrose content ranged from 1.6 to 95.4 mg g ―1 with 13 PIs containing greater than 70 mg g ―1 and 14 PIs having less than 10 mg g ―1 . The stachyose content ranged from 0.2 to 69.6 mg g ―1 with 14 PIs containing less than 10 mg g ―1 stachyose. The high sucrose and low stachyose types are the most valuable for breeding specialty soybeans for soyfood and animal feed. In addition, 30 PIs were identified as having high concentrations of glucose or fructose as major sugars. This new class of high glucose or fructose has not been reported before. While soybean germplasm with unique sugar profiles may be useful for future breeding and genetic research, environmental effects on sugar stability will need to be further investigated.

Differential Wilting among Soybean Genotypes in Response to Water Deficit

Abstract: Genotypic differences for canopy wilting have been reported for soybean [Glycine max (L.) Merr.], but no wilting data have been published, and mechanisms for differences remain unresolved. In fi eld studies in 2002 and 2003, differences for wilting among 19 genotypes were consistent across years. Plant introductions (PI 416937 and PI 471938) were among the slowest wilting genotypes, and breeding lines (93705-34 and 93705-95) were among the fastest wilting. Row spacing (18 vs. 80 cm wide) did not affect wilting, indicating that lateral rooting did not contribute to genotypic differences. In a separate fi eld study, volumetric soil water content at 15- and 50-cm depths was generally greater for slow-wilting PI 416937 than for fast-wilting 93705-95. Wilting for both genotypes responded similarly to soil water content (r 2 = 0.63–0.74). In a growth chamber study, transpiration declined similarly for fast- and slow-wilting genotypes in response to soil water defi cit. Wilting response to soil water was the same for slow-wilting PI 416937 and fast-wilting genotypes 93705-34 and A5959. Slow-wilting 93705-36 began wilting at a lower soil water content than did PI416937, 93705-34, and A5959, indicating that more than one mechanism may be responsible for slow wilting.

Composition, Vigor, and Proteome of Mature Soybean Seeds Developed under High Temperature

Abstract: The effects of high temperature treatment on soybean [Glycine max (L.) Merr.] seed composition, vigor, and proteome were investigated using mature dry seeds harvested from plants grown in environment-controlled chambers. High day/night temperatures (37/30°C) from stages R5 through R8 altered ratios of individual fatty acids to total fatty acid compared to the control (27/18°C). Concentration of sugars decreased, but total protein and phytic acid concentration were unchanged. High temperature resulted in a greater propor- tion of abnormal seeds, but normal-appearing seed exhibited reduced germination and vigor. Proteomic analysis detected 20 protein identities whose accumulations were changed by the high temperature. Fourteen spots were identified as seven subunits of seed storage proteins. The remaining six proteins were identified as those responding to abiotic stresses or having a function in respiration: (i) sucrose binding protein, (ii) Class III acidic endochitinase, (iii) heat shock protein (HSP22), (iv) late embryo abundant protein, (v) Bowman-Birk proteinase inhibitor, and (vi) formate dehydrogenase. High temperature during seed development changed soybean seed composition and decreased seed vigor, but also changed seed protein expression profiles.

Genetic Variability in Nitrogen Use Efficiency of Spring Barley

Abstract: Increasing costs of N fertilizers and the negative impact of excessive N on the environment have made improvement in nitrogen use effi ciency (NUE) a desirable goal in barley ( Hordeum vul-gare L.) breeding. Seventeen replicated trials, each consisting of 15 to 20 genotypes, were per-formed across different environments in Alberta, Canada from 1998 to 2007 to determine genetic variability in NUE. Further, 25 genotypes were grown at six environments in 2007 for analysis of the pattern of genotypic variation for NUE. Analysis of variance revealed signifi cant effects of genotype and environment on NUE. The majority of the phenotypic variation in NUE was accounted for by genotypic variance and heri-tability estimates for this trait ranged from 0.5 to 0.86. Genotypes H97097001001, H96014002, ‘Vivar’, and ‘Xena’, were superior in NUE, yield-ing 47 to 48 kg kg –1 N as compared to about 35 kg kg –1 N yield for the relatively ineffi cient geno-types. There was no clear distinction between two-rowed and six-rowed types in NUE, but rather signifi cant differences were observed among genotypes within each spike-type group. Reduction in N fertilizer requirements in barley while maintaining yield may be achieved through breeding by targeting increased yield potential in association with higher NUE.Y. Anbessa, P. Juskiw, J. Nyachiro, and J. Helm, Field Crop Develop-ment Centre (FCDC), Alberta Agriculture and Rural Development, Lacombe, AB, Canada; A. Good, Dep. of Biological Sciences, Univ., of Alberta, Edmonton, AB, Canada. Received 26 Sept. 2008. *Cor-responding author (yadeta.kabeta@gov.ab.ca).

Inheritance of Resistance to the Soybean Aphid in Soybean PI 200538

Abstract: The soybean aphid (Aphis glycines Matsumura) is a major soybean (Glycine max (L.) Merr.) insect pest. Soybean plant introduction (PI) 200538 has strong resistance to the aphid. The objectives of our research were to determine the inheritance of resistance and to map gene(s) controlling resis- tance in PI 200538. F 2 populations developed from crosses between PI 200538 and three sus- ceptible genotypes were tested for resistance and with DNA markers. F 2 plants from the cross 'Ina' × PI 200538 segregated 114 resistant to 37 susceptible and F 2 plants from the cross 'Wil- liams 82' × PI 200538 segregated 203 resistant to 65 susceptible when tested for resistance to soybean aphid biotype 1. F 2 plants from the cross LD02-4485 × PI 200538 segregated 167 resistant to 62 susceptible when tested for resistance to biotype 2. These populations fi t a 3:1 genetic ratio (P = 0.89, 0.78, and 0.52, respectively) with resistance dominant over sus- ceptibility. Segregation among F 2:3 families from the crosses supported the dominant resistance gene hypothesis. The gene mapped to soybean linkage group F, fl anked by the simple sequence repeat marker loci Satt510, Soyhsp176, Satt114, and Sct_033, located in the same region as the aphid resistance gene Rag2. Since the resis- tance gene in PI 200538 also gave resistance to soybean aphid biotypes 1 and 2, it is pos- sible that the gene is Rag2 and not a new aphid resistance gene. Therefore, PI 200538 may be an additional source of Rag2.

Effect of Maturity on Seed Composition in the Early Soybean Production System as Measured on Near-Isogenic Soybean Lines

Abstract: The effect of maturity (time to maturity) on seed composition in soybean (Glycine max (L.) Merr.) genotypes is not well understood because maturity is generally confounded with genotypic background. Therefore, the effects of maturity on seed composition were estimated in two sets of near isogenic soybean lines ('Clark' and 'Har- osoy'), where the maturity of each line within a set varied, but all had a common genotypic background. There was a positive linear relation- ship between protein concentration and maturity among isolines of the Clark set in 2004 (r 2 = 0.75; P ≤ 0.001) and 2005 (r 2 = 0.63; P ≤ 0.001). How- ever, in Harosoy isolines there was no relation- ship between protein and maturity. There was a negative linear relationship between oil concen- tration and maturity for Clark (in 2004, r 2 = 0.82, P ≤ 0.001; in 2005, r 2 = 0.91, P ≤ 0.0001) and Harosoy (in 2004, r 2 = 0.19, P ≤ 0.05; in 2005, r 2 = 0.36, P ≤ 0.01). Maturity had greater effects on seed composition than maximum tempera- ture. The results indicate that the relationship between seed composition and maturity was different between the Clark and Harosoy sets of isolines. However, the overall mean of protein and oil concentration was not different between genotypic backgrounds. This information will be useful for soybean breeding in developing new germplasm for seed composition.

Enhanced Tolerance to Multiple Abiotic Stresses in Transgenic Alfalfa Accumulating Trehalose

Abstract: Alfalfa (Medicago sativa L.) is an important forage crop in many countries with high biomass production and the third-most-cultivated crop in the United States, with high protein content and potential use as biofuel. Here we describe the use of a chimeric translational fusion of yeast trehalose-6-phosphate synthase (EC 2.4.1.15) and trehalose-6-phosphate phosphatase (EC 3.1.3.12) genes to engineer stress tolerance in alfalfa. The gene fusion was overexpressed using either the constitutive 35S promoter or the stress-regulated rd29A promoter. Transgene insertion in the genome was checked by polymerase chain reaction and transcript expression by reverse transcription polymerase chain reaction. Several independent transgenic plants were selected in the presence of kanamycin and further analyzed. Yeast gene encoding trehalose-6-phosphate synthase (TPS1)-yeast gene encoding trehalose-6-phosphate phosphatase (TPS2) gene expression under the 35S promoter led to plants with stunted growth and less biomass, whereas TPS1-TPS2 expression driven by the rd29A promoter improved growth and provoked a significant increase in plant biomass at the foliage level in the different transgenic lines. Trehalose accumulated in all the different lines at similar levels under stress conditions. Transgenic plants displayed a significant increase in drought, freezing, salt, and heat tolerance. This is the first time that genetic engineering of trehalose metabolism is reported in alfalfa and demonstrates that it can improve multiple stress protection in this crop. Thus, the yeast TPS-TPP fusion protein represents a great potential for generating stress-tolerant crop plants for agriculture.

Summer drought survival strategies and sustainability of perennial temperate forage grasses in Mediterranean areas.

Abstract: Perennial grasslands provide numerous agroenvironmental benefits due to continuous soil cover. In Mediterranean areas, chronic summer drought is expected to increase as a result of climate changes. Plant adaptations that protect meristematic tissues include dehydration delay, dehydration tolerance, and summer dormancy. Summer dormancy can only be reliably tested in plants not subjected to water deficit. Under summer irrigation, complete dormancy is manifested by cessation of growth in association with full senescence of foliage and induced dehydration of leaf bases. Incomplete dormancy occurs when leaf growth is partially constrained and associated with moderate levels of foliage senescence. Summer dormancy is under hormonal control and is induced under increasing photoperiod and temperature. Recent results show that drought cannot induce summer dormancy under early-spring short days, although a water deficit under late-spring long days reinforces it and could enhance drought survival. Dehydration tolerance and dormancy are independent phenomena. Summer dormancy has been correlated with superior survival after severe summer droughts in many perennial grass species. This trait has potential for improving cultivars able to meet agronomic and environmental goals.

Mapping and Confirmation of a New Allele at Rpp1 from Soybean PI 594538A Conferring RB Lesion–Type Resistance to Soybean Rust

Abstract: Soybean rust, caused by Phakopsora pachyrhizi (H. Sydow & Sydow), is a destructive soybean (Glycine max (L.) Merr.) disease and identifi - cation of new resistance genes is essential for effective rust management. Our research objectives were to map and confi rm the loca- tion of resistance gene(s) in PI 594538A using a population of 98 F 3:4 lines from a cross between PI 594538A (reddish-brown (RB) lesions) and the susceptible cultivar Loda (tan (TAN) lesions). The lines were inoculated with the P. pachyrhizi isolate ZM01-1 from Zimbabwe. The RB resis- tance in PI 594538A mapped on linkage group G as a single dominant gene. This gene is likely an allele of Rpp1 or a new closely linked gene because it mapped within 1 cM of Rpp1 and ZM01-1 produced RB lesions on PI 594538A and TAN lesions on PI 200492, the original source of Rpp1. The mapping of the new Rpp1 allele, named Rpp1-b, was confi rmed in a sec- ond population.

Genetic variability of transpiration response to vapor pressure deficit among soybean cultivars

Abstract: Simulation studies have demonstrated that the existence of a limitation on maximum transpiration rate (TR) at high air vapor pressure deficit (VPD) in water-limited conditions could result in significant yield increases. A genotype of soybean [Glycine max (L.) Merr.] (PI 416937) has been identified both with a slow-wilting phenotype in the field and limited TR above a VPD breakpoint (BP) of 2 kPa. Until now, there has been no full documentation of any other soybean genotype that has a restriction on TR at high VPD. The objective of this study was to extend the observations on TR response to VPD to a wider genetic base. Seven soybean genotypes were studied: three cultivars of broad genetic background and four new lines of diverse backgrounds with PI 416937 in their pedigrees. Data collected across a VPD range of ∼1 to ∼3.5 kPa for each genotype showed a two-segment TR response to VPD for two cultivars, neither of which was derived from PI 416937. Since three progeny of PI 416937 expressed slow-wilting in the field, these results indicate that the slow-wilting phenotype may also result from a mechanism other than the TR response to VPD. Identification of two new genetic selections with limitation of TR at high VPD indicates there is more than one genetic source for this potentially beneficial trait for water-limited environments.

Understanding Soybean Maturity Groups in Brazil: Environment, Cultivar Classification, and Stability

Abstract: Maturity classifi cation is an important concept to provide the best allocation of resources for soybean [Glycine max (L.) Merr.] research and commercialization. A similar maturity group system used in North America is being used for some seed companies in Brazil and needs research to improve its use. This study evaluated the maturity stability of 48 midwestern and 40 southern Brazilian commercial cultivars ranging from North American maturity groups VI to VIII at 15 locations. Relative maturity groups were attributed to all cultivars. All trials were planted in the fi rst half of November. The effect of location was very important in infl uencing the number of days to maturity, number of days to fl owering and reproductive growth period (RGP). The genotype × environment interaction, although statistically signifi cant, was much lower than the individual effects of environment and genotype for all traits and regions. Genotype × latitude and genotype × altitude, considering also years of evaluation, were generally low or nonsignifi cant. A recommended list was developed of the most stable genotypes and, consequently, of the most suitable check genotypes for each maturity group classifi cation in the southern and midwestern regions. Results indicate that the use in Brazil of a maturity group system similar to that used in North America to classify soybean genotypes is an effi cient method for describing relative maturity on a broad environmental basis.

Interspecies transfer of resistance to anthracnose in lentil (Lens culinaris Medic.).

Abstract: Lentil, Lens culinaris subsp. culinaris Medic., is an important legume crop on the Canadian prairies. Anthracnose, a fungal disease caused by Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore, is a major barrier to seed yield and quality in lentil. Pathogenicity testing has revealed two races, Ct1 and Ct0, of C. truncatum in western Canada. No cultivar or landrace of cultivated lentil has been reported with resistance to anthracnose race Ct0. A search for Ct0 resistance in the wild species identified a high frequency of resistant accessions in Lens ervoides (Brign.) Grande. To incorporate higher levels of resistance from L. ervoides to the two races of anthracnose, a cross was made between a susceptible L. culinaris cultivar, Eston, and a resistant accession of L. ervoides germplasm, L-01-827A, which has both Ct0 and Ct1 resistance. Embryo rescue technique was used to obtain an F 1 hybrid. Single-seed descent was used to advance the individual F 2 plants to F 7:8 recombinant inbred lines. Evidence of transfer of resistance to both anthracnose races Ct1 and Ct0 from the wild species to cultivated lentil is presented. Chi-square tests of goodness of fit indicated that resistance to race Ct1 and race Ct0 may be conferred by two recessive genes. However, these results may be skewed due to variable fertility encountered in development of the population. Selection of resistant lines for use in pyramiding genes in breeding programs should result in a more durable level of resistance to anthracnose in lentil.

Characterization, Genetic Variation, and Combining Ability of Maize Traits Relevant to the Production of Cellulosic Ethanol

Abstract: Maize (Zea mays L.) stover has been identified as an important feedstock for the production of cellulosic ethanol. Our objectives were to measure hybrid effect and combining ability patterns of traits related to cellulosic ethanol production, determine if germplasm and mutations used for silage production would also be beneficial for feedstock production, and examine relationships between traits that are relevant to selective breeding. We evaluated grain hybrids, germplasm bred for silage production, brown-midrib hybrids, and a leafy hybrid. Yield and composition traits were measured in four environments. There was a 53% difference in stover yield between commercial grain hybrids that were equivalent for other production-related traits. Silage germplasm may be useful for increasing stover yield and reducing lignin concentration. We found much more variation among hybrids than either in vitro ruminal fermentability or polysaccharide concentration. Correlations between traits were mostly favorable or nonexistent. Our results suggest that utilizing standing genetic variation of maize in breeding programs could substantially increase the amount of biofuels produced from stover per unit area of land.