Agronomic changes of soybean cultivars released during 1950 to 2006 in Heilongjiang Province

To clarify the aim characteristics for soybean high-yield breeding,soybean cultivars released during 1950 to 2006 in Heilongjiang Province were used to investigate agronomic characteristics. The results show that there was significantly positive correlation between yield and year of cultivar release. The soybean yield increased by 1.27% per year. The number of pod and seed per plant also increased by 0.54% and 0.98% per year, respectively, while 100-seed weight didn't change with year of cultivar release. Over the more 50 years of genetic improvement, soybean height decreased by 14.0%, plant dry weight and harvest index increased by 25.8% and 35.1%, respectively. Resistances of lodging, diseases and pests of seed were improved as well. Furthermore, these characteristics were significantly related to yield and yield components. However, the crop growth rate and LAI (leaf area index) during the V3 (the third trifoliolate) to the R2 (the full bloom) stage had no linear relationship with year of cultivar release, and consequently, yield. It was suggested that plant dry weight, harvest index and lodging resistance are crucial for genetic yield improvement.