Pod dehiscence of soybean: Identification of quantitative trait loci

The dehiscence of pods (shattering) prior to harvest is an undesirable trait of soybean, Glycine mau (L.) Merr. Pod dehiscence (PD) is relatively uncommon in modern North American soybean cultivars, but is often observed when unimproved germplasm or the wild species, G. soja Siebold & Zucc., are used as parents to introgress useful genes or to develop genetically diverse breeding populations. In light of the potential for efficient selection using DNA markers, the objective of this study was to identify quantitative trait loci (QTL) that condition resistance to PD. A map of 140 linked restriction fragment length polymorphism (RFLP) markers was constructed using 120 F-4-derived lines from a soybean population (Young x PI 416937) that segregated for resistance to PD. These lines were scored for PD on a visual scale of 1 to 10 at both Athens, Georgia, and Windblow, North Carolina, in 1994. Heritability of pod dehiscence was 92%. Associations of marker loci with QTL that condition resistance to PD were tested using homozygous RFLP class means in a single-factor ANOVA. A total of five putatively independent RFLP markers were associated with PD at both locations and in a combined analysis over locations. A single RFLP locus on linkage group J of the USDA/Iowa State University map accounted for 44% of the variation in PD score. Epistasis was observed between one pair of significant marker loci. These results establish the genomic location of one major and a few minor QTL, identify an epistatic interaction, and indicate transgressive segregation which is plausibly the result of susceptibility alleles contributed by the resistant parent.