WIDE HYBRIDIZATION BETWEEN BRAZILIAN SOYBEAN CULTIVARS AND WILD PERENNIAL RELATIVES

Employing a different culture strategy, we obtained a greatly improved frequency of embryo rescue in intersubgeneric soybean hybrids. Succes sful crosses were obtained in 31 different genotype combinations betwe en nine Brazilian soybean lines as the female parents and 12 accession s from Glycine canescens, G. microphylla, G. tabacina and G. tomentell a. The hybrid pod retention rate dropped to about 10% during the first 8 days after pollination and stayed largely unchanged up to the 20th day. Immature harvested seeds fell into three size groups: Group 1, sm aller than 1.3 mm (mostly empty seed coats); Group 2, 1.9-5.0 mm; Grou p 3, larger than 5 mm (from selfing). A total of 90 putative hybrid em bryos were rescued using a highly enriched B5 medium to nourish the ne wly dissected embryos. The growing embryos were then placed in a high osmotic, modified B5 medium to induce maturation and dormancy. Schenk and Hildebrandt medium was used to germinate the dormant, partially de hydrated, physiologically mature embryos. Approximately 37% of the res cued embryos developed into plantlets in vitro, and approximately 8% g rew into mature plants in the greenhouse. Morphological, cytological a nd isoenzyme patterns confirmed the hybrid status of all seven mature plants, all of which were generated using G. tomentella G 9943 as the paternal parent. It was observed that all soybean lines crossed with G 9943 were capable of producing mature hybrid plants. There was no cor relation between the initial size of Group 2 seeds and plant survival rate. The hybrids were cloned by grafting and treated with colchicine. One of the treated plants displayed chromosome doubling.