No abstract

HighlightWe identified different expression levels of FT5a, an ortholog of FLOWERING LOCUS T, as the molecular basis of a quantitative trait locus that promotes flowering under long-day conditions in soybean.

In yellow soybean, seed coat pigmentation is inhibited by post-transcriptional gene silencing (PTGS) of chalcone synthase (CHS) genes. A CHS cluster named GmIRCHS (Glycine max inverted-repeat CHS pseudogene) is suggested to cause PTGS in yellow-hilum cultivars. Cold-induced seed coat discoloration (CD), a commercially serious deterioration of seed appearance, is caused by an inhibition of this PTGS upon exposure to low temperatures. In the highly CD-tolerant cultivar Toyoharuka, the GmIRCHS structure differs from that of other cultivars. The aim of this study was to determine whether the variation of GmIRCHS structure among cultivars is related to variations in CD tolerance. Using two sets of recombinant inbred lines between Toyoharuka and CD-susceptible cultivars, we compared the GmIRCHS genotype and CD tolerance phenotype during low temperature treatment. The GmIRCHS genotype was related to the phenotype of CD tolerance. A QTL analysis around GmIRCHS showed that GmIRCHS itself or a region located very close to it was responsible for CD tolerance. The variation in GmIRCHS can serve as a useful DNA marker for marker-assisted selection for breeding CD tolerance. In addition, QTL analysis of the whole genome revealed a minor QTL that also affected CD tolerance.

The number and distribution of branches in soybean plants influence seed yield through effects on the efficiency of light utilization as well as on tolerance to lodging. We have developed recombinant inbred lines (RILs) from a cross between two experimental determinant lines, which differ in branching number. The 172 RILs were divided into four maturity groups according to their alleles for two maturity loci, E1 and E3, and were planted separately to avoid confounding effects of competition. The late-maturity RIL groups with the E1 genotype were grown in two different locations, whereas the early-maturity RIL groups with the e1 genotype were planted at one location. Analysis of all lines resulted in the identification of five quantitative trait loci (QTLs) for branching number, designated qBr1 to qBr5. Among these QTLs, qBr1 and qBr2 were mapped to the proximal regions of the E1 and E3 loci, respectively. The other three QTLs were mapped to regions distant from any known maturity loci and were detected only in the presence of the E1 genotype, indicating that they interact with qBr1. Our results suggest that branching number might be controlled genetically by the identified QTLs, even though the maturity loci substantially affect branching phenotype.

Lodging tolerance (LT) is an important trait for high yield and combine-harvesting efficiency in soybean [Glycine max (L.) Merr.]. Many previous studies have investigated quantitative trait loci (QTLs) for lodging score (LS) in soybean. Most of the investigated QTLs were located in the proximal region of maturity or growth habit loci. The aim of this study was to identify genetic factors for LT not associated with maturity or growth habit. QTL analysis was performed using a recombinant inbred line (RIL) population derived from a cross between ‘Toyoharuka’ (TH), a lodging-tolerant cultivar, and ‘Toyomusume’ (TM). The genotypes of TH and TM were estimated as both e1e2E3E4 and dt1. The average LS over 4 years was used for QTL analysis, identifying a major and stable QTL, qLS19-1, on chromosome 19. The LS of the near-isogenic line (NIL) with the TH allele at Sat_099, the nearest marker to qLS19-1, was significantly lower than the NIL with the TM allele at that position. The TH allele at Sat_099 rarely had a negative influence on seed yield or other agronomic traits in both NILs and the TM-backcrossed lines. Our results suggest that marker-assisted selection for qLS19-1 is effective for improving LT in breeding programs.