Leaf shape polymorphism and its relationship to other characteristics of wild soybean (Glycine soja) in China

The Chinese genebank contains 6169 wild soybean (Glycine soja) accessions collected from 25 provinces. In this study, leaf shape and a suite of other morphological characteristics were analyzed in order to examine the relationship between leaf shape and other characteristics of wild soybeans. The accessions were classified into the following six groups based on leaf shape: accessions with round leaves, ovate-round leaves, elliptical leaves, lanceolate leaves, line leaves and leaves classified as `other'. Correlations between the leaf shape and other qualitative characteristics were analyzed. Differences on quantitative traits among groups were evaluated. We found that accessions with round leaves were primarily characterized by obvious main stems, gray pubescence, white flowers, non-sooty seed coats, yellow seed coats, brown hilum, high 100-seed weight, low protein content and high oil content. In contrast, accessions with line leaves were characterized by twining stems, brown pubescence, purple flowers, sooty seed coats, black seed coats, black hilum, low 100-seed weight, high protein content and low oil content. We infer that there exists a continuous evolutionary spectrum based on the leaf length-to-width ratio of wild soybeans where round leaf and line leaf accessions represent diametric extremes. Along this evolutionary spectrum, accessions with line leaves tend to be wild types, while accessions with round leaves represent more recently evolved varieties. Finally, accessions with lanceolate, ellipse, ovate-round and other leaves occupy their own specific positions along this evolutionary spectrum.