[Show abstract][Hide abstract] ABSTRACT: In Hokkaido, northern Japan, soybean [Glycine max (L.) Merr.] crops are damaged by cold weather. Chilling temperatures result in the appearance of cracking seeds (CS) in soybean crops, especially those grown in eastern and northern Hokkaido. Seed coats of CS are severely split on the dorsal side, and the cotyledons are exposed and frequently separated. CS occurrence causes unstable production because these seeds have no commodity value. However, little is known about the CS phenomenon. The aims of this study were to identify the cold-sensitive stage associated with CS occurrence and to develop a method to select CS-tolerant lines. First, we examined the relationship between chilling temperatures after flowering and CS occurrence in field tests. The average temperature 14 to 21 days after flowering was negatively correlated with the rate of CS. Second, we evaluated differences in CS tolerance among soybean cultivars and breeding lines in field tests. 'Toyohomare' and 'Toiku-238' were more CS-tolerant than 'Yukihomare' and 'Toyomusume'. Third, we developed a selection method in which plants were subjected to 21-day chilling-temperature treatment from 10 days after flowering in a phytotron. This enabled comparisons of CS tolerance among cultivars. This selection method will be useful for breeding CS-tolerant soybeans.
[Show abstract][Hide abstract] ABSTRACT: 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.
Theoretical and Applied Genetics 10/2010; 122(3):633-42. · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pod set, a critical process for legume crop productivity, is sensitive to environmental stress such as low or high temperature or drought. At higher latitudes, pod set at low temperatures is one of the most important processes for efficient soybean production. The present study was carried out to determine which flower developmental stage was most sensitive to low temperature and how low temperature interrupts the pod setting process. Soybean flowers at various developmental stages were subjected to low temperatures, and the percentage elongation of pods was subsequently measured. Two low temperature-sensitive stages were found. The first was an early developmental stage approximately 12.5 days before the anthesis of individual flowers. The second stage occurred 3–4 days before anthesis. An investigation of the pollen grain number on stigma suggests that insufficient pollination causes low pod set under low temperature stress at both temperature-sensitive stages. Tetrad-shaped abnormal pollen grains were observed when flowers were subjected to low temperature at the first sensitive stage; thus, this stage might be the tetrad stage or the stage prior to tetrad formation. Furthermore, at the first sensitive stage, pollen development deficiency was one of the causes of poor pod set under low temperature conditions.
Environmental and Experimental Botany 02/2010; 69(1):56-62. · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Low temperature is among the critical environmental factors that limit soybean production. To elucidate the genetic basis for chilling tolerance and identify useful markers, we conducted quantitative trait loci (QTL) analysis of seed-yielding ability at low temperature in soybean (Glycine max), using artificial climatic environments at usual and low temperatures and recombinant inbred lines derived from a cross between two contrasting cultivars in terms of chilling tolerance. We identified a QTL of a large effect (LOD > 15, r (2) > 0.3) associated with seed-yielding ability only at low temperature. The QTL was mapped near marker Sat_162 on linkage group A2, where no QTL for chilling tolerance has previously been identified. The tolerant genotype did not increase the pod number but maintained the seed number per pod and single seed weight, namely, the efficiency of seed development at low temperature. The effect of the QTL was confirmed in a segregating population of heterogeneous inbred families, which provided near-isogenic lines. The genomic region containing the QTL also influenced the node and pod numbers regardless of temperature condition, although this effect was not primarily associated with chilling tolerance. These results suggest the presence of a new major genetic factor that controls seed development specifically at low temperature. The findings will be useful for marker-assisted selection as well as for understanding of the mechanism underlying chilling tolerance in reproductive organs.
Theoretical and Applied Genetics 04/2009; 118(8):1477-88. · 3.51 Impact Factor