Highly specific seed market classes for cowpea and other grain legumes exist because grain is most commonly cooked and consumed whole. Size, shape, color, and texture are critical features of these market classes and breeders target development of cultivars for market acceptance. Resistance to biotic and abiotic stresses that are absent from elite breeding material are often introgressed through crosses to landraces or wild relatives. When crosses are made between parents with different grain quality characteristics, recovery of progeny with acceptable or enhanced grain quality is problematic. Thus genetic markers for grain quality traits can help in pyramiding genes needed for specific market classes. Allelic variation dictating the inheritance of seed size can be tagged and used to assist the selection of large seeded lines. In this work we applied 1,536-plex SNP genotyping and knowledge of legume synteny to characterize regions of the cowpea genome associated with seed size. These marker-trait associations will enable breeders to use marker-based selection approaches to increase the frequency of progeny with large seed. For 804 individuals derived from eight bi-parental populations, QTL analysis was used to identify markers linked to 10 trait determinants. In addition, the population structure of 171 samples from the USDA core collection was identified and incorporated into a genome-wide association study which supported more than half of the trait-associated regions important in the bi-parental populations. Seven of the total 10 QTLs were supported based on synteny to seed size associated regions identified in the related legume soybean. In addition to delivering markers linked to major trait determinants in the context of modern breeding, we provide an analysis of the diversity of the USDA core collection of cowpea to identify genepools, migrants, admixture, and duplicates.
Core Ideas Incorporation of resistance to Charcoal Rot is an important goal for soybean breeding programs. Single nucleotide polymorphisms and haplotypes associated with Charcoal Rot resistance will be an important breeding component. Genome wide association studies that use haplotype information can afford new insights into the traits determinants. Incorporation of resistance to Charcoal Rot (CR), caused by the soil‐borne fungus Macrophomina phaseolina (Tassi) Goid., is an important goal for soybean [Glycine max (L.) Merr.] breeding programs. However, the limited accessible information on sources and hereditary mechanisms related to resistance has impeded progress, as reflected in the lack of commercial CR‐resistant soybean varieties around the world. The identification of single nucleotide polymorphisms (SNPs) and haplotypes associated with CR resistance will be an important breeding component. In this study, a genome wide association study (GWAS) was undertaken to identify genomic regions controlling CR resistance in a soybean association mapping panel, using single nucleotide polymorphism (SNP) markers and haplotype information. The soybean varieties (N = 169) were field‐evaluated on a site with a history of heavy CR infestation in Citrus Research Center and Agricultural Experiment Station (CRC‐AES) at the University of California, Riverside, USA, and genotyped with 6000 SNP markers. Symptoms of mortality were evaluated for 12 wk after the first symptoms of infection. Two SNP‐based haplotypes were found associated with CR in the genome‐wide haplotype association analysis. Two associations of stable haplotypes for CR, haplotype TAC and CGA of the markers Gm08_18909193_A_G, Gm08_44422211_T_C, and Gm19_34320762_A_C were identified. These markers are associated with other important disease resistance genes in the soybean genome. These findings will allow breeders to improve tropical soybean breeding for CR resistance. A haplotype‐based GWAS can provide more information into the genetic basis of CR resistance that could not be captured by the single marker approach.
RESUMO -O milho (Zea mays L.) é uma planta de clima tropical que exige calor e umidade para produzir satisfatoriamente e proporcionar rendimentos compensadores. Diversos fatores podem comprometer a germinação das sementes e a emergência de plântulas no campo, merecendo destaque a semeadura em solos com baixas temperaturas. Em regiões que predominam condições de baixas temperaturas, seria importante o uso de sementes mais tolerantes a essa condição de estresse. Sementes de milho apresentam variabilidade genética para a germinação a baixas temperaturas. O objetivo deste trabalho foi classificar genótipos de milho quanto a tolerância das sementes à baixa temperatura de germinação, identificando àqueles com potencial para utilização em semeadura precoce. Avaliaram-se 16 genótipos provenientes do programa de melhoramento de milho da empresa KSP Sementes e Pesquisas Ltda., sendo 10 linhagens em diferentes estádios endogâmicos, seis populações de fecundação aberta e três híbridos simples comerciais, recomendados para semeadura precoce na Região Sul do Brasil. A avaliação da qualidade fisiológica das sementes foi feita pelos testes de germinação, primeira contagem de germinação, comprimento de plântula, biomassa seca, área foliar e radicular nas temperaturas de 25°C e 10°C. Foram realizadas análises eletroforéticas para os sistemas isoenzimáticos da fosfatase ácida, esterase e peroxidase. Os resultados permitiram classificar os genótipos quanto à tolerância das sementes à baixa temperatura, evidenciando que há variabilidade entre eles e potencialidades para serem usados em semeadura precoce na região sul do Brasil.Termos para indexação: Zea mays, baixa temperatura, emergência precoce. EVALUATION OF CORN GENOTYPES FOR USE IN EARLIER SOWING UNDER LOW TEMPERATURESABSTRACT -Corn (Zea mays L.) is a characteristic plant of tropical climates that requires heat and humidity to produce satisfactorily and to provide compensatory incomes. Several factors can compromise seed germination and plant emergence in the field, and it is important to consider sowing in soils with low temperatures. In regions where low temperature conditions predominate, the use of more tolerant seeds to this stress condition would be important. Corn seeds present genetic variability for germination at low temperatures. The objective of this study was to classify corn genotypes for germination at low soil temperatures. Sixteen 16 genotypes from the breeding corn program of the company KSP Sementes and Pesquisas Ltda. were evaluated, 10 lines at different endogamic stages, six cross pollination populations and three 3 single commercial hybrids, recommended for earlier sowing in southern Brazil. The physiological quality was evaluated by the tests of germination, first count of germination, plant growth, dry matter, shoot and root area AT 25°C and 10°C. The eletroforetic patterns of the isoenzimatic systems of the acid phosphatase,
The root-knot nematode (RKN) species Meloidogyne javanica (MJ) causes substantial root damage and yield loss in susceptible soybean [Glycine max (L.) Merr.] cultivars. In this study, a genome wide association study (GWAS) was undertaken to identify genomic regions controlling RKN resistance in a soybean associationmapping panel, using single nucleotide polymorphism (SNP) markers and haplotype information. This study was carried out with a sample (n = 124) from the Coodetec soybean gene bank, including some commercial Brazilian varieties.For the phenotypic evaluations MJ inoculum was obtained from roots of cultivar CD 206, a highly susceptible soybean used to maintain MJ for studies at Coodetec. The cultivars CD 208 and BRS CONQUISTA were used as resistant checks while CD 206, R7, and Nidera NA 5909 RG were used as susceptible checks and all 124 lines were genotyped with 6,000 SNP markers. MJ resistance determinants in the soybean panel were linked to SNPs with significant effects, with nine SNPs distributed along chromosomes 7, 13, and 20. The observed average MJ resistance in the group of soybean entries with haplotype GCT, ACC, ACT, and GCC in the markers Gm20_44446670_G_A, Gm13_29739984_C_A and Gm07_8166605_T_C, respectively, represents moderately resistant genotypes. Gm13_29739984_C_A and Gm07_8166605_T_C discriminated resistant and susceptible cultivars better than the marker Gm20_44446670_G_A. These results are particularly promising for soybeanbreeding programs, by not only identifying new resistance-associated haplotypes, but also suggesting new genetic mechanisms in RKN-resistance sources.
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