Botany and Cytogenetics of Soybean

Soybean [Glycine max (L.) Merr.], an economically important dicot legume, is a member of the family Fabaceae and belongs to the genus Glycine Willd. Based on classical and molecular taxonomy, the genus Glycine has been divided into two subgenera; the subgenus Soja (Moench) F.J. Hermann includes soybean and its wild annual progenitor G. soja Sieb. & Zucc. Both species contain 2n = 40 chromosomes, are cross-compatible, produce fertile F1 plants, and belong to the primary gene pool. The subgenus Glycine consists of 26 wild perennial species. Vegetative and reproductive morphology of soybean has been examined extensively. The cytogenetic knowledge of soybean lags far behind that of other model economically important crops (viz. rice, maize, wheat, tomato), because its somatic chromosomes are symmetrical and only one pair of satellite chromosomes can be identified. Molecular linkage maps have been associated with specific chromosomes, and soybean genome has been sequenced. The soybean breeders, worldwide, are confined to crossing within the primary gene pool; thus, genetic base of soybean is very narrow. Wild perennial Glycine species of the tertiary gene pool have been recently exploited to broaden the genetic base of modern soybean cultivars.