US Germplasm Research Articles

Performance and phenotypic stability of maize hybrids containing exotic introgressions in multi‐environment trials

AbstractMaize (Zea mays L.) grown in the US Midwest contains only a small fraction of the genetic diversity present in the species. Maize populations from other parts of the world may contain genetic variation that could be used to improve or increase the diversity of US germplasm. This study was conducted to assess the performance and phenotypic stability of hybrids containing diverse exotic introgressions across North American environments. Doubled haploid (DH) lines were created by the Germplasm Enhancement of Maize project from backcross 1 families that used 27 open‐pollinated populations from Latin America as donor parents and PHZ51, a non‐Stiff Stalk inbred developed in Iowa, as the recurrent parent. DH lines were testcrossed with LH195, a Stiff Stalk inbred developed in Iowa, and hybrid field trials were performed at 24 environments in the United States and Canada. Experimental hybrids had variable flowering time, plant and ear height, and test weight, but none had significantly greater yield than the PHZ51 × LH195 hybrid. The slopes of linear reaction norm models were significantly lower for the experimental hybrids than the US‐adapted reference hybrids for three traits: yield, growing degree units (GDU) to anthesis, and GDU to silking. The results suggest that unfavorable alleles and phenotypic stability should be considered when exotic open‐pollinated populations are used in US maize breeding.

Genetic diversity and population structure analyses and genome-wide association studies of photoperiod sensitivity in cotton (Gossypium hirsutum L.).

Genetic diversity and population structure analyses showed progressively narrowed diversity in US Upland cotton compared to land races. GWAS identified genomic regions and candidate genes for photoperiod sensitivity in cotton. Six hundred fifty-seven accessions that included elite cotton germplasm (DIV panel), lines of a public cotton breeding program (FB panel), and tropical landrace accessions (TLA panel) of Gossypium hirsutum L. were genotyped with cottonSNP63K array and phenotyped for photoperiod sensitivity under long day-length conditions. The genetic diversity analysis using 26,952 polymorphic SNPs indicated a progressively narrowed diversity from the landraces (0.230) to the DIV panel accessions (0.195) and FB panel (0.116). Structure analysis in the US germplasm identified seven subpopulations representing all four major regions of the US cotton belt. Three subpopulations were identified within the landrace accessions. The highest fixation index (FST) of 0.65 was found between landrace accessions of Guatemala and the Plains-type cultivars from Southwest cotton region while the lowest FST values were between the germplasms of Mid-South and Southeastern regions. Genome wide association studies (GWAS) of photoperiod response using 600 phenotyped accessions identified 14 marker trait associations spread across eight Upland cotton chromosomes. Six of these marker trait associations, on four chromosomes (A10, D04, D05, and D06), showed significant epistatic interactions. Targeted genomic analysis identified regions with 19 candidate genes including Transcription factor Vascular Plant One-Zinc Finger 1 (VOZ1) and Protein Photoperiod-Independent Early Flowering 1 (PIE1) genes. Genetic diversity and genome wide analyses of photoperiod sensitivity in diverse cotton germplasms will enable the use of genomic tools to systematically utilize the tropical germplasm and its beneficial alleles for broadening the genetic base in Upland cotton.

Meta‐analysis of apple (Malus × domestica Borkh.) fruit and juice quality traits for potential use in hard cider production

Societal Impact StatementThe production of hard cider is a burgeoning industry in North America. However, traditional European cider‐specific apples are largely unsuitable for production in modern systems and have not been widely adopted. Evaluation of the biochemical variability in apples can provide a better characterization of varieties for use in hard cider production. Many varieties exhibited extensive variability in biochemical traits. Varieties with high phenolics and acidity displayed greater plasticity of these traits between seasons, which supports the concept of “vintage quality” and opens new marketing opportunities. This study provides valuable insight for apple producers to integrate cider‐specific and nonspecific varieties into their production systems.Summary The North American fermented beverage market has undergone extensive growth in the fermented apple juice (hard cider) sector over the last decade. Traditional hard cider producing regions such as England, France, and Spain have historically utilized cider‐specific apples that have desirable balances between sugar, organic acid, and phenolics. However, in North America, culinary apples (lower acidity and phenolics) are predominantly used, and information distinguishing the varieties with novel use for hard cider production is lacking. In this study, we evaluated variation of four major apple biochemical traits (total soluble solids, pH, titratable acidity, and total phenolics) as they relate to use for hard cider production by using a meta‐analysis approach. We analyzed the variation in cider quality traits across 47 published works and more than 800 unique apple varieties, including an additional analysis of 142 varieties from cider apple germplasms in the United States. The biochemical traits of many varieties exhibited plasticity, and the characterization of a subset of varieties using two cider classification system revealed that most belonged to the “sweet” or “sharp” (acidic) categories rather than “bitter” (high phenolic content). We also compared the classification of a subset of varieties from two US germplasm resources across two seasons and found varieties that have high percent phenolics and/or malic acid experienced greater biochemical plasticity and potential classification change across vintages. Ultimately, this work provides information regarding the variability in apple biochemical traits and also suggests a unique opportunity for producers to market “vintage” quality.

A chromosome-scale reference genome of trifoliate orange (Poncirus trifoliata) provides insights into disease resistance, cold tolerance and genome evolution in Citrus.

SUMMARYTrifoliate orange (Poncirus trifoliata), a deciduous close relative of evergreen Citrus, has important traits for citrus production, including tolerance/resistance to citrus greening disease (Huanglongbing, HLB) and other major diseases, and cold tolerance. It has been one of the most important rootstocks, and one of the most valuable sources of resistance and tolerance genes for citrus. Here we present a high‐quality, chromosome‐scale genome assembly of P. trifoliata. The 264.9‐Mb assembly contains nine chromosomal pseudomolecules with 25 538 protein‐coding genes, covering 97.2% of the estimated gene space. Comparative analyses of P. trifoliata and nine Citrus genomes revealed 605 species‐specific genes and six rapidly evolving gene families in the P. trifoliata genome. Poncirus trifoliata has evolved specific adaptation in the C‐repeat/DREB binding factor (CBF)‐dependent and CBF‐independent cold signaling pathways to tolerate cold. We identified candidate genes within quantitative trait loci for HLB tolerance, and at the loci for resistance to citrus tristeza virus and citrus nematode. Genetic diversity analysis of Poncirus accessions and Poncirus/Citrus hybrids shows a narrow genetic base in the US germplasm collection, and points to the importance of collecting and preserving more natural genetic variation. Two phenotypically divergent Poncirus accessions are found to be clonally related, supporting a previous conjecture that dwarf Flying Dragon originated as a mutant of a non‐dwarfing type. The high‐quality genome reveals features and evolutionary insights of Poncirus, and it will serve as a valuable resource for genetic, genomic and molecular research and manipulation in citrus.

Genetic Diversity, Population Structure, and Marker-Trait Association for Drought Tolerance in US Rice Germplasm.

Drought is a major constraint in some rice-growing areas of the United States. Its impact is most severe at the reproductive stage resulting in low grain yield. Therefore, assessment of genetic and phenotypic variation for drought tolerance in US rice germplasm is necessary to accelerate the breeding effort. Evaluation of 205 US rice genotypes for drought tolerance at the reproductive stage revealed tolerant response in rice genotypes Bengal, Jupiter, Cypress, Jazzman, Caffey, and Trenasse. Harvest index and fresh shoot weight were identified as important traits to explain the majority of variability among the genotypes under drought tolerance. Genotyping with 80 SSR markers indicated a low level of genetic diversity in US germplasm. Population structure analysis grouped the genotypes into eight clusters. The genotypes from California, Louisiana, and Arkansas formed distinct subgroups. Texas genotypes were similar to those from Louisiana and Arkansas. Marker-trait association analysis showed significant association of RM570 and RM351 with grain yield, spikelet fertility, and harvest index whereas shoot dry weight showed association with RM302 and RM461. The drought-tolerant genotypes identified in this study and the SSR markers associated with drought tolerance attributes will be helpful for development of improved drought-tolerant rice varieties through marker assisted selection.

Haplotype Characterization of the sd1 Semidwarf Gene in United States Rice.

Genomic data from diverse germplasm used for application in targeted breeding germplasm. Six SNPs identified that can characterize all haplotypes present at SD1 locus in diverse rice. Three alleles of the SD1 gene identified in US rice germplasm including two semidwarf alleles. Two SNPs identified and validated that differentiate the SD1 allele present in US germplasm. KASP assays designed for both SNPs for use in high-throughput breeding applications. Plant height is an important target in US rice (Oryza sativa L.) breeding programs and the large effect of the sd1 semidwarf gene makes it a suitable target for marker-assisted selection. Although the deletion underlying the semidwarf allele is known and a gel-based DNA marker is available, this marker is not ideal for applied breeding because of throughput and cost constraints. The objectives of this study were to characterize the haplotype diversity at the SD1 locus within US rice germplasm and develop a single nucleotide polymorphism (SNP) assay for breeding applications. The International Rice Research Institute (IRRI) SNP-Seek database was used to characterize the haplotype diversity present at the SD1 locus across a set of rice accessions and seven haplotypes were identified. The US rice germplasm was not well represented in the IRRI database, so a set of six SNPs was identified that could differentiate all detected haplotypes. These SNPs were designed into Kompetitive allele specific polymerase chain reaction (KASP) assays and screened across 359 elite US genotypes. Of the seven haplotypes, two were present within the US germplasm, one of which was the semidwarf deletion allele. A third haplotype was observed within the US medium-grain germplasm and demonstrated to be a semidwarf allele derived from the induced mutation in the 'Calrose76'. Two SNPs were identified that distinguish the three SD1 haplotypes present in the US germplasm. These SNPs were validated across the US germplasm and two biparental populations.

Evaluation of Genetic Diversity of Proso Millet Germplasm Available in the United States using Simple‐Sequence Repeat Markers

Proso millet (Panicum miliaceum L.) is the best rotational crop in most dryland production areas in the semiarid US High Plains because of the highest water use efficiency among all cereal crops and short growing season. In the United States, it is used for birdseed, but it is used mostly for human consumption in Asia and Europe. Genomic resources and genetic research of this crop are limited. There is no report of molecular marker‐based genetic diversity analysis of the US germplasm, which is important for its genetic improvement. The objective of this study was to evaluate genetic diversity of US proso millet germplasm based on DNA markers. A set of 90 proso millet genotypes (landraces and cultivars) and 100 simple‐sequence repeat (SSR) markers were used. Cluster analysis was based on unweighed pair‐group method with arithmetic average (UPGMA) and principal component analysis (PCA) using NTSYSpc software. A total of 1287 alleles with size range from 40 to 1500 bp were amplified by the 100 SSR markers. The US proso millet germplasm used in this report is highly genetically diverse. The genotypes formed one major and two minor groups, which correspond to their geographic origin, pedigree, and morphoagronomic traits with few exceptions. All the cultivars developed in the United States remained together in a subcluster within Group 2. Many of these SSR markers with high resolving power were very informative and could be useful for further genetic diversity studies of proso millet. This study would have significant implications for future proso millet genetic improvement.

Genetic diversity, population structure and marker trait associations for seed quality traits in cotton (Gossypium hirsutum).

Cottonseed contains 16% seed oil and 23% seed protein by weight. High levels of palmitic acid provides a degree of stability to the oil, while the presence of bound gossypol in proteins considerably changes their properties, including their biological value. This study uses genetic principles to identify genomic regions associated with seed oil, protein and fibre content in upland cotton cultivars. Cotton association mapping panel representing the US germplasm were genotyped using amplified fragment length polymorphism markers, yielding 234 polymorphic DNA fragments. Phenotypic analysis showed high genetic variability for the seed traits, seed oil range from 6.47-25.16%, protein from 1.85-28.45% and fibre content from 15.88-37.12%. There were negative correlations between seed oil and protein content.With reference to genetic diversity, the average estimate of FST was 8.852 indicating a low level of genetic differentiation among subpopulations. The AMOVA test revealed that variation was 94% within and 6% among subpopulations. Bayesian population structure identified five subpopulations and was in agreement with their geographical distribution. Among the mixed models analysed, mixed linear model (MLM) identified 21 quantitative trait loci for lint percentage and seed quality traits, such as seed protein and oil. Establishing genetic diversity, population structure and marker trait associations for the seed quality traits could be valuable in understanding the genetic relationships and their utilization in breeding programmes.

Ex situ conservation of Holstein-Friesian cattle: Comparing the Dutch, French, and US germplasm collections

Holstein-Friesian (HF) gene bank collections were established in France, the Netherlands, and the United States to conserve genetic diversity for this breed. Genetic diversity of HF collections within and between countries was assessed and compared with active male HF populations in each country by using pedigree data. Measures of genetic diversity such as probability of gene origin inbreeding and kinship were calculated. The cryobanks have captured substantial amounts of genetic diversity for the HF compared with the current populations. A substantial part of the US, French, and Dutch collections seems to be genetically similar. On the other hand, the US collection in particular represents an interesting reservoir of HF genes of the past. Gene banks can play an important role in conserving genetic diversity within livestock breeds over time, and may support industry in the future when needed.

Polymorphism in the GBSS gene affects amylose content in US and European rice germplasm

The present study was conducted to investigate the relationship between waxy allelic forms and amylose in European and US rice germplasm. These allelic forms were defined according to the single-nucleotide polymorphisms (SNP) found in the leader intron 5′ splice site (G → T), exon 6 (A → C) and exon 10 (C → T). The combination of these three SNPs accounted for 89.2% of the variation in apparent amylose content in a pedigree of 85 US rice varieties and 93.8% of the variation among 279 accessions in a European germplasm collection. The allelic forms TAC and TCC were found in low amylose varieties. All varieties with intermediate levels of apparent amylose had the GCC allele. High levels of apparent amylose varieties had either the GAT and GAC allele. The sequence AG TTATA in the intron 1 distinguished the low amylose varieties from the other classes regardless of any other base changes. Intermediate amylose varieties can be distinguished from those with high apparent amylose by changes in either exon 6 or exon 10. However the simplest interpretation of the data is that the tyrosine/serine change in exon 6 is responsible for the lower levels of Granule bound starch synthase (GBSS) protein and thus lower levels of amylose in intermediate vs. high amylose verities.

Development of unique and novel lines for early-maturing hybrids: moving GEM germplasm northward and westward

Future maize (Zea mays L.) genetic gains are dependent on the incorporation of unique and useful genetic diversity to breeding programs actively improving germplasm and developing cultivars. Our ultimate goal is to increase the genetic diversity currently available in early maturing maize hybrids by developing novel lines that can be utilized competitively in the northern US Corn Belt. A long-term breeding project (EarlyGEM) was initiated to move US Germplasm Enhancement Maize (GEM) germplasm northward and westward. Nine out of 152 breeding crosses were adapted and data from one breeding cross is presented. Five hundred BC1:S1 lines derived from (AR16026:S17-66-1-B × ND2000) × ND2000 were advanced, selected, and crossed to several commercial testers for early and late generation hybrid testing. Experiments were arranged in various partially balanced lattice designs and grown across 23 North Dakota (ND) environments. Data showed experimental GEM-derived hybrids had better grain yield (10.4 vs. 9.2 t ha−1), test weight (72.5 vs. 70.1 kg h L−1), extractable starch (67.8 vs. 64.2%) and fermentable starch, grain oil (4.3 vs. 3.5%), and grain protein (10.5 vs. 9.4%) when compared to popular hybrids at similar grain moisture at harvest. This is the first research incorporating GEM-derived tropical and late-temperate genetic materials for inbred line development representing a relative maturity (RM) below 90 days. As a consequence of these breeding efforts GEM materials were adapted to the northern US Corn Belt and are not only sources of useful and unique novel genetic diversity but also competitive products for industry use as requests for experimental EarlyGEM lines have been extensive. This research has practical implications with regards to new ways of conducting maize breeding for high latitudes.

Broadening the genetic base of European maize heterotic pools with US Cornbelt germplasm using field and molecular marker data

Maize (Zea mays L.) breeders are concerned about the narrowing of the genetic base of elite germplasm. To reverse this trend, elite germplasm from other geographic regions can be introgressed, but due to lack of adaptation it is difficult to assess their breeding potential in the targeted environment. The objectives of this study were to (1) investigate the relationship between European and US maize germplasm, (2) examine the suitability of different mega-environments and measures of performance to assess the breeding potential of exotics, and (3) study the relationship of genetic distance with mid-parent heterosis (MPH). Eight European inbreds from the Dent and Flint heterotic groups, 11 US inbreds belonging to Stiff Stalk (SS), non-Stiff Stalk (NSS), and CIMMYT Pool 41, and their 88 factorial crosses in F(1) and F(2) generations were evaluated for grain yield and dry matter concentration. The experiments were conducted in three mega-environments: Central Europe (target mega-environment), US Cornbelt (mega-environment where donor lines were developed), and Southeast Europe (an intermediate mega-environment). The inbreds were also fingerprinted with 266 SSR markers. Suitable criteria to identify promising exotic germplasm were F(1) hybrid performance in the targeted mega-environment and F(1) and parental performance in the intermediate mega-environment. Marker-based genetic distances reflected relatedness among the inbreds, but showed no association with MPH. Based on genetic distance, MPH, and F(1) performance, we suggest to introgress SS germplasm into European Dents and NSS into European Flints, in order to exploit the specific adaptation of European flint germplasm and the excellent combining ability of US germplasm in European maize breeding programs.

Spring barley accessions with dual spot blotch and net blotch resistance

Spot blotch and net blotch are common foliar diseases of barley in the upper midwestern United States and are capable of causing significant reductions in both the yield and quality of the crop. Currently, there are no cultivars grown in the region that possess high levels of resistance to net blotch, and recent evidence suggests that the durable spot blotch resistance present in six-row malting types may be vulnerable to virulent isolates of Cochliobolus sativus. To identify new sources of resistance, over 5000 accessions of barley from the USDA National Small Grains Collection and Texas barley breeding program were evaluated for their reaction to spot blotch and net blotch in field nurseries established at Fargo and Langdon, North Dakota, respectively. Eighteen accessions that exhibited a true spring type habit and did not have any known midwestern US germplasm in their parentage were evaluated in additional field and greenhouse tests. All 18 accessions were confirmed to carry field resistance to both diseases, but their levels of resistance varied. Seedling tests also were conducted in the greenhouse to determine whether the selected accessions carried broader resistance against different pathotypes of each pathogen. Several accessions were susceptible to one or more of the pathogen isolates, indicating potential vulnerability of their field resistance. Of the 18 accessions evaluated in this study, 8 (CIho 2291, CIho 7021, PI 58228, PI 83794, PI 428626, PI 434771, PI 467387, and Tx 7934) exhibited the broadest resistance across different pathogen isolates as revealed in the seedling tests and may be the best sources of dual spot blotch and net blotch resistance for barley breeding programs. Key words: Hordeum vulgare, Cochliobolus sativus, Pyrenophora teres, field resistance, host-parasite interactions. Les taches helminthosporiennes et les rayures réticulées sont des maladies foliaires courantes de l'orge dans les États du Haut-Midwest américain où elles peuvent entraîner d'importantes baisses tant sur le plan du rendement que sur celui de la qualité. À ce jour, aucun des cultivars semés dans cette région ne possède de taux élevé de résistance aux rayures réticulées, et certains cas récents suggèrent que la résistance durable aux taches helminthosporiennes affichée par certains types d'orge de brasserie à six rangs peut s'avérer précaire lorsque mis en présence d'isolats virulents de Cochliobolus sativus. Afin de déterminer de nouvelles sources de résistance, plus de 5000 accessions d'orge provenant de la National Small Grain Collection (USDA) et du programme de sélection du Texas ont été évaluées relativement à leur réaction aux taches helminthosporiennes et aux rayures réticulées dans des pépinières volantes à Fargo et à Langdon, dans le Dakota du Nord. De plus, 18 accessions qui affichaient un développement caractéristique des types de printemps, et qui ne possédaient dans leur ascendance aucun germoplasme « Midwest » connu, ont été évaluées au cours d'essais en serre et en champ. On a confirmé que les 18 accessions étaient porteuses de résistance horizontale, mais que les taux de résistance variaient. Des tests en serre ont également été effectués sur des plantules afin de déterminer si les accessions choisies étaient plus résistantes à différents pathovars de chaque agent pathogène. Plusieurs accessions étaient réceptives à l'égard de un ou de plusieurs isolats d'agent pathogène, indiquant une possible précarité de leur résistance horizontale. Des 18 accessions étudiées au cours de cette étude, 8 (CIho 2291, CIho 7021, PI 58228, PI 83794, PI 428626, PI 434771, PI 467387 et Tx 7934) affichaient le taux de résistance le plus élevé relativement à divers isolats d'agents pathogènes, comme l'ont montré les tests effectués sur les plantules. Dans le cadre de programmes de sélection, ces dernières peuvent par conséquent s'avérer les meilleures sources de résistance aux taches helminthosporiennes et aux rayures réticulées pour l'orge. Mots-clés : Hordeum vulgare, Cochliobolus sativus, Pyrenophora teres, résistance horizontale, interactions hôte-parasite.

Evaluation of chlorophyll fluorescence as a tool for the identification of drought tolerance in upland cotton

Chlorophyll fluorescence (CF) is one tool used by researchers to quantify plant water status during periods of limited water availability. The research reported herein was designed to evaluate a CF-based protocol as a tool for use in cotton, Gossypium spp. breeding programs for the identification of drought tolerant genotypes. Twenty genotypes were selected to represent diverse and distinct US germplasm pools. Replicated tests were performed in Lubbock and College Station, TX in 2006 and 2007. Dryland and irrigated treatments, as main plots, were applied in a randomized complete block design, split to genotypes. CF measurements were taken at mid-bloom and late bloom growth stages. Source leaf tissue was harvested at predawn and subjected to high temperature incubation with CF measurements subsequently taken hourly for 5 h. Drought stressed plants had not mobilized their carbohydrate reserves from their source leaves overnight and thus maintained cell viability and therefore higher CF values throughout the incubation and measurement period with the opposite being true for non-stressed plants. Fiber lint yield and fiber properties were measured for comparison with the CF data. Genotype × treatment effects complicated the classification of genotypic response to drought. Few and inconsistent correlations were found among CF values and lint yield or fiber properties. Data suggested that this procedure provides little potential in selecting plants for drought tolerance when plants are grown under field culture.

An updated ‘Essex’ by ‘Forrest’ linkage map and first composite interval map of QTL underlying six soybean traits

DNA marker maps based on single populations are the basis for gene, loci and genomic analyses. Individual maps can be integrated to produce composite maps with higher marker densities if shared marker orders are consistent. However, estimates of marker order in composite maps must include sets of markers that were not polymorphic in multiple populations. Often some of the pooled markers were not codominant, or were not correctly scored. The soybean composite map was composed of data from five separate populations based on northern US germplasm but does not yet include 'Essex' by 'Forrest' recombinant inbred line (RIL) population (E x F) or any southern US soybean cultivars. The objectives were, to update the E x F map with codominant markers, to compare marker orders among this map, the Forrest physical map and the composite soybean map and to compare QTL identified by composite interval maps to the earlier interval maps. Two hundred and thirty seven markers were used to construct the core of the E x F map. The majority of marker orders were consistent between the maps. However, 19 putative marker inversions were detected on 12 of 20 linkage groups (LG). Eleven marker distance compressions were also found. The number of inverted markers ranged from 1 to 2 per LG. Thus, marker order inversions may be common in southern compared to northern US germplasm. A total of 61 QTL among 37 measures of six traits were detected by composite interval maps, interval maps and single point analysis. Seventeen of the QTL found in composite intervals had previously been detected among the 29 QTL found in simple interval maps. The genomic locations of the known QTL were more closely delimited. A genome sequencing project to compare Southern and Northern US soybean cultivars would catalog and delimit inverted regions and the associated QTL. Gene introgression in cultivar development programs would be accelerated.

A USA–Africa collaborative strategy for identifying, characterizing, and developing maize germplasm with resistance to aflatoxin contamination

Aflatoxin contamination of maize by Aspergillus flavus poses serious potential economic losses in the US and health hazards to humans, particularly in West Africa. The Southern Regional Research Center of the United States Department of Agriculture, Agricultural Research Service (USDA-ARS-SRRC) and the International Institute of Tropical Agriculture (IITA) initiated a collaborative breeding project to develop maize germplasm with resistance to aflatoxin accumulation. Resistant genotypes from the US and selected inbred lines from IITA were used to generate backcrosses with 75% US germplasm and F(1) crosses with 50% IITA and 50% US germplasm. A total of 65 S(4) lines were developed from the backcross populations and 144 S(4) lines were derived from the F(1) crosses. These lines were separated into groups and screened in SRRC laboratory using a kernel-screening assay. Significant differences in aflatoxin production were detected among the lines within each group. Several promising S(4) lines with aflatoxin values significantly lower than their respective US resistant recurrent parent or their elite tropical inbred parent were selected for resistance-confirmation tests. We found pairs of S(4) lines with 75-94% common genetic backgrounds differing significantly in aflatoxin accumulation. These pairs of lines are currently being used for proteome analysis to identify resistance-associated proteins and the corresponding genes underlying resistance to aflatoxin accumulation. Following confirmation tests in the laboratory, lines with consistently low aflatoxin levels will be inoculated with A. flavus in the field in Nigeria to identify lines resistant to strains specific to both US and West Africa. Maize inbred lines with desirable agronomic traits and low levels of aflatoxin in the field would be released as sources of genes for resistance to aflatoxin production.

The Impact of US and CGIAR Germplasm on Maize Production in China

Wide adoption of a few kinds of homogeneous germplasm would reduce crop genetic diversity, increase crop vulnerability to stresses, and reduce the stability of crop production. The introduction and utilization of foreign germplasm is a sustainable solution for broadening the genetic diversity and promoting periodical replacement of varieties. The genetic contribution and economic impact of foreign germplasm, particularly those of US and CGIAR (Consultative Group on International Agricultural Research, referred to as the CG system) materials, on China's maize production are evaluated on the basis of an analysis of variety pedigree information from 20 major maize-producing provinces in China from 1982 to 1997. The results indicated that the contribution of US and CG germplasm to Chinese maize production continues to increase, particularly CG germplasm, which has shown a rapid increasing trend since the 1990s. If the genetic contribution of US germplasm is increased by 1%, maize yield will gain by 0.2% (0.01 t ha −1). If contribution of CG germplasm, which has greater production potential, is increased by 1%, maize yield will gain by 0.025 t ha −1. A policy should be implicated by the government in this direction to encourage breeders to focus more on the use and improvement of CG germplasm. The US germplasm has been utilized extensively in China so that it can offer germplasm resources for maize breeding efforts.

Registration of N98–4445A Mid‐Oleic Soybean Germplasm Line

Soyabean (Glycine max) germplasm line N98-4445A, which originated as an F5 single plant selection from the three-way cross N94-2473 × (N93-2007-4 × N92-3907), was developed and released in 2002 by the USDA-ARS in cooperation with the North Carolina Agricultural Research Service. N78-4445A has group IV maturity, indeterminate growth habit, white flowers and tawny pubescences. Seeds are shiny yellow with brown hila. N98-4445A has moderate levels of resistance to Soyabean mosaic virus. This line has a concentration of oleic acid in the seed oil that is approximately 550 g/kg, which is 340-380 g/kg greater than commercial soyabean cultivars and 47 g/kg more than the highest oleic acid concentration available in US germplasm collection. The germplasm will be a useful genetic resource for breeding mid-oleic soyabean cultivars, i.e. those with oleic acid concentrations between 400 and 700 g/kg. Increased oleic acid in this line causes a correlated decrease in polyunsaturated fatty acids, giving the added advantage of linolenic acid concentrations less than 30 g/kg.

Genetic analysis infers Dt loci underlie resistance to Fusarium solani f. sp. glycines in indeterminate soybeans

Improved resistant cultivars are being developed to better withstand the sudden death syndrome (SDS) of soybean (Glycine max L. Merr.) caused by Fusarium solani (Mart.) Sacc. f. sp. glycines (Fsg) (renamed F. virguliforme). Field trials to identify and select SDS-resistant cultivars take several years and are expensive. Selection of seedlings in the greenhouse and marker assisted selection are faster and cheaper. Selection for loci contributing SDS is well established for southern US germplasm sources (Forrest, Pyramid) but untested in northern germplasm. The aim was to find DNA markers associated with loci contributing seedling resistance to F. solani in the northern germplasm cultivars Minsoy and Noir. The greenhouse assay used plants grown for 3 wk in F.solani inoculated soil. Disease severity (DS) was recorded for 2000 recombinant inbred lines (RIL) from Minsoy × Noir1 (M×N) after F. solani infestation and compared to the DS of non-infested controls. Minsoy was partially resistant and Noir1 was relatively susceptible to F. solani. The heritability of DS was 48%. Comparison of alleles at 247 loci with the DS trait identified three regions associated with DS. Two regions within a 16 cM region of linkage group L (U14) were identified by markers SAT99 (P = 0.0006, R2 = 7%) and SATT6 (P = 0.0013, R2 = 5%). One region on linkage group C1 (U10b_ was identified by A063_1 (P = 0.0011, R2 = 5%). Interacting loci explained an additional 12% (A280 and SAT99) and 10% (R28 and SATT6) of the variability in DS, mainly by increasing resistance in susceptible class at each quantitative trait loci (QTL). These loci jointly explain the major portion (34%) of heritable resistance to F.solani. The QTL did not correspond with the known loci that condition resistance in the field in southern US germplasm. The QTL were in regions of the genome that were previously determined to alter determinacy, plant morphology, leaf shape, stem thickness, plant height, maturity and water use. Here Minsoy was taller, had thicker stems, produced more root mass and more shoot mass than Noir 1 during Fsg infestati on. Height (r = 0.15, P = 0.03), root weight (r = 0.3, P = 0.0002) and shoot weight r = 0.4, P = 0.0001) were significantly negatively correlated with resistance to SDS. Therefore, we conclude the SDS resistance is a pleiotropic effect of shoot and root characters in Minsoy and Noir that may confound selection for resistance to SDS in North American germplasm. Key words: Determinacy, genetic map, soil borne disease, Fusarium solani f. sp. glycines, soybean, Fusarium virguliforme

Characterization of the end-use Quality of Soft Wheat Cultivars from the Eastern and Western US Germplasm ‘Pools’

AbstractSoft wheat (Triticum aestivum L.) improvement could be enhanced by the identification of germplasm with superior end-use quality traits. Due to the geographic and historical separation of eastern and western US soft wheat germplasm ‘pools’, genetic differences in end-use quality may exist among cultivars arising from these two pools. To identify such differences, 30 US soft wheat cultivars were evaluated in ‘head-to-head’ trials over 3 years in Washington state. Cultivars were classified as: eastern soft red winter (SRW), eastern soft white winter (ESWW), western soft white (WSWW) and western Club. These four soft wheat cultivar classifications clearly differed systematically for some of the quality traits examined. The Club wheat cultivar group had the highest flour yield and flour ash. The Club group also had the lowest mixograph dough water absorption. Milling score (which incorporates break flour yield) was highest for Club and ESWW. Eastern soft red and white wheat cultivar groups had lower flour ash and alkaline water retention capacity (AWRC) compared to the western Club and soft white wheats; ESWW had the lowest AWRC of any classification. Cookie diameter was greatest for the ESWW group, followed by the SRW and Club groups (which were not significantly different), and then by the WSWW group. Individual cultivars with exceptional quality traits were also identified. These results indicate that the four US soft wheat germplasm pools differ, and they may be valuable genetic resources for ‘inter-pool’ wheat improvement.