Ten cultivars of local vegetable-type soybean (Dadacha bean lines) were examined for physiological and ecological traits, and for morphological traits associated with growth and yield characteristics in 2007 and 2009. Most of the cultivars of Dadacha bean lines had green hypocotyls and white flowers, excluding two cultivars which had purple hypocotyls and purple flowers. The seed coats of the cultivars of Dadacha bean lines were brown and seeds were flat and elliptic, with wrinkles at various levels. Although immature pods were harvested as edamame 35 days after flowering from early to late August, the harvest delayed over 5-6 days in 2009. Characteristics associated with yield were better in 2009 and also showed clear variations among cultivars. There were significant positive correlations between days before flowering and yield-associated characteristics, i.e., total plant weight, weight of pod with stem, number of pods and weight of pods. Significant highly positive correlations were found among the characteristics of the number of pods, total plant weight, number of pods, and weight of pods. A medium-type cultivar, Shirayama-dadacha, showed slightly higher yield ability. The pods weighed around 140-185 g per plant. In consideration of their influence on eating quality, free amino acids and sugars in immature cotyledons were analyzed. Twenty-three amino acids, including GABA, AABA, and ornithine, were detected. Immature cotyledons of all cultivars of Dadacha bean lines contained over 800 mg total free amino acids, higher than those of 2 normal vegetable-type soybean cultivars. Three amino acids, glutamic acid, asparagine and alanine, were abundant, comprising about 55%. Among sugar molecules, sucrose, glucose, fructose and inocitol were detected in immature cotyledons of all vegetable-type cultivars. In both 2007 and 2009, immature cotyledons of the cultivars of Dadacha bean lines had total sugar of 4-5 g/100 g FW, while those of normal vegetable-type cultivars had relatively low sugar contents, about 3 g/100 g FW. Analysis of variance revealed that variations in the contents of total free amino acids and total sugars among cultivars were highly significant, and year to year variation of these contents was also significant. Significant positive correlations between the contents of total free amino acids and total sugar were found.

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We performed quantitative trait locus (QTL) analysis for cold tolerance at the booting stage (CT), heading date (HD) and culm length (CL) using 84 recombinant inbred lines derived from a cross combination between temperate japonicas Hokkai-PL9 (cold-tolerant) and Hokkai287 (cold-sensitive). CT was evaluated by fertility after cold water treatment. Three QTLs for CT were detected on chromosomes 1 (qCTB1.1 and qCTB1.2) and 8 (qCTB8.1), and Hokkai-PL9 allele at all three QTLs increased the level of CT. Phenotypic variance explained (PVE) of qCTB1.1, qCTB1.2 and qCTB8.1 were 18.8%, 11.8% and 14.2%, respectively. Three QTLs for HD were detected on chromosomes 2 and 3 (two QTLs), and nine QTLs for CL were detected on chromosomes 1, 2, 3 (three QTLs), 8, 9 (two QTLs) and 11. No QTLs for HD and CL were detected in the same region as QTLs for CT. The effects of the Hokkai-PL9 allele of QTLs for CT significantly increased CT, suggesting that QTL combination is effective for CT improvement.

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