58 YEARS OF GENETIC-IMPROVEMENT OF SHORT-SEASON SOYBEAN CULTIVARS IN CANADA

Soybean [Glycine mar (L.) Merr.] production in short-season areas has increased greatly because of improvements in cultivars and production practices. Previous studies of genetic improvement in soybean have rep orted yield increases of 0.5 to 1% per year. To evaluate the genetic i mprovement of short-season germplasm, 41 cultivars ranging from maturi ty group 000 to 0, released from 1934 to 1992, were grown for 8 statio n-years in Ontario and Quebec. Yield, maturity, plant height, lodging score, 100-seed weight, seed protein and oil levels, and yield stabili ty were regressed on year of release to determine if improvements have been made. Yield has been improved about 0.5% per year during the per iod under study; however, since 1976 yield has been improved about 0.7 % per year. There is evidence that the rate of genetic improvement of seed yield is accelerating. Significant lodging reduction was also obs erved. Seed protein levels have been reduced 4 g kg(-1) yr(-1) and see d oil levels have increased 4 g kg(-1) yr(-1). Although yield has been increased, yield stability has remained constant.