Due to high costs of irrigation, limited availability of irrigation water in many locations and/or lack of irrigation capabilities, genetic improvement for drought tolerance is an effective method to reduce yield loss in soybean [Glycine max (L.) Merr.]. Slow wilting and minimal yield reduction under drought are important traits in evaluating drought tolerance. Two maturity group III soybean plant introductions (PIs, PI 567690 and PI 567731) and two elite cultivars (DKB38-52 and Pana) were evaluated with and without irrigation on a sandy soil. Drought was imposed by withholding irrigation at full bloom and continued until moderate wilting was shown by the fast leaf wilting in the check cultivar, Pana. Then, irrigation was resumed until maturity. Genotypes were scored for leaf wilting during the stress period, and yields were assessed at the end of the growing season and used to calculate a drought index. Yields of the exotic PIs were lower than those of the checks under both drought and well-watered conditions. However, the PIs exhibited significantly lower wilting and less yield loss under drought (higher drought index) than check cultivars. The two PIs may have useful genes to develop drought-tolerant germplasm and cultivars and maybe useful in genetic and physiological studies to decipher mechanisms responsible for improving yield under limited water availability.

This study aimed to elucidate the role played by Enterobacter asburiae KE17 in the growth and metabolism of soybeans during copper (100 μm Cu) and zinc (100 μm Zn) toxicity. When compared to controls, plants grown under Cu and Zn stress exhibited significantly lower growth rates, but inoculation with E. asburiae KE17 increased growth rates of stressed plants. The concentrations of plant hormones (abscisic acid and salicylic acid) and rates of lipid peroxidation were higher in plants under heavy metal stress, while total chlorophyll, carotenoid content and total polyphenol concentration were lower. While the bacterial treatment reduced the abscisic acid and salicylic acid content and lipid peroxidation rate of Cu-stressed plants, it also increased the concentration of photosynthetic pigments and total polyphenol. Moreover, the heavy metals induced increased accumulation of free amino acids such as aspartic acid, threonine, serine, glycine, alanine, leucine, isoleucine, tyrosine, proline and gamma-aminobutyric acid, while E. asburiae KE17 significantly reduced concentrations of free amino acids in metal-affected plants. Co-treatment with E. asburiae KE17 regulated nutrient uptake by enhancing nitrogen content and inhibiting Cu and Zn accumulation in soybean plants. The results of this study suggest that E. asburiae KE17 mitigates the effects of Cu and Zn stress by reprogramming plant metabolic processes.

Korea is a centre of genetic diversity for both cultivated [Glycine max (L.) Merr] and wild (Glycine soja Sieb. and Zucc.) soybeans. Wild soybean is native to some of the 3 000 islands surrounding the Korean peninsula. The objective of this study was to estimate genetic diversity of wild soybeans collected from 24 inhabited islands off the southern coast of Korea. Forty simple sequence repeat markers covering the 20 soybean chromosomes were used to estimate genetic diversity among 66 wild accessions collected from 24 islands. Accessions collected from the islands were similar to the Korean mainland accessions for diversity index. Molecular variation between island and mainland populations was about 8% (P = 0.001) and 91.6% within wild soybean populations. Genetic variation (P = 0.001) among and within the island wild soybean populations was 9.8% and 90.2%, respectively. Wild soybeans from the islands may be specifically adapted to the adverse conditions such as wind, flooding, salt and drought and may have useful genes tolerance to various abiotic stresses and resistance to biotic traits.Key words: genetic diversity -Glycine soja -soybeansoybean germplasm -wild soybean Wild soybean (Glycine soja Sieb. & Zucc.), known as the direct progenitor of cultivated soybean [Glycine max (L.) Merr.], is widely distributed in China, North Eastern Russia, Korea, Japan, and Taiwan (Hymowitz and Singh 1987, Chung andSingh 2008). Wild soybean accessions originating from different geographical regions harbour genetic differences. Gorman (1984) examined more than 100 G. soja accessions for 15 enzymes from various geographical regions and concluded that Korean accessions have significantly higher diversity than those from China. High genetic diversity in Korean G. soja accessions has been demonstrated by comparing variation in agronomic traits and molecular markers (Park and Hur 1979, Kim et al. 2003, Lee et al. 2005, Kim and Park 2005. Analysis of nine enzymes (Aco, Aph, Dia, Enp, Est, Idh, Lap, Mpi, and Pgm) in 383 accessions from Japan and 28 accessions from Korea showed that Korea is a major centre of genetic diversity and may be the centre of origin of wild soybean (Abe et al. 1992). Yu and Kiang (1993) compared genetic variation at 35 loci for 17 isozymes and the protein Kunitz trypsin inhibitor among 172 wild soybean accessions collected from six regions of South Korea and concluded that South Korea is a major centre of diversity for G. soja. Single sequence repeat (SSR) markers have been used to examine genetic diversity in wild soybean accessions of South Korea (Choi et al. 1999, Cho et al. 2006. Both studies concluded that genetic diversity was very high in the South Korean wild soybean populations. Lee et al. (2008) compared genetic diversity among G. soja accessions (n = 274) collected from broad regions of South Korea and China using 46 SSR markers covering all 20 soybean linkage groups. Their results indicated that genetic diversity index among wild accessions was high and similar for both countries.Soybean b...