It was attempted, though in vain, to cross soybean with Glycine species of the subgenus Glycine.
Utilization of wild species for improving their cultivated counterparts is steadily increasing in various crops (HARLAN, 1976). Exploitation of the wild progenitors is the most reasonable approach since a cultigen and its wild progenitor are genetically members of the same species and gene transfer between them is a relatively simple task. Exploitation of other wild species, such as those which belong to the secondary or tertiary gene pools of the cultigen (HARLAN & DE WET, 1971) is much more difficult since various types of isolating mechanisms that prevent gene flow between different biological units must be overcome. On the other hand, because of genetic remoteness of these wild species from the cultigen there is a good possibility that they possess variation in characteristics of economic value which is missing in the cultivated germplasm, e.g., pest and disease resistance.
The genus Glycine WILLD. is currently divided into two subgenera, Glycine and Soja (MOENCH) F. J. HERM. The subgenus Soja includes the cultivated soybean, Glycine max (L.) MERR1LL and its wild progenitor G. soja SIEB. and Zucc. The subgenus Glycine contains six parennial wild species: Glycine canescens F. J. HERM., G. Clandestina WENDL., G. falcata BENTH., G. latrobeana (MEISSM.) BENTH., G. tabacina (LABILL.) BENTH. and G. tomentella HAYATA (HYMOWITZ & NEWELL, 1979). In the past few years a sizeable collection of species belonging to the subgenus Glycine has been assembled at the Department of Agronomy, University of Illinois, Urbana, and a study aiming at assessing intra and interspecific variation was initiated (NEWELL & HYMOWITZ, 1978). However, from a plant breeding point of view it is important to have concrete information not only regarding the ranges of variation but also the possible exploitation of these species for improving the cultivated soybean. In other words, it is crucial to determine the rate of crossability between the cultigen and these wild species, the behavior of F 1 hybrids and their progeny.