Heterosis,Combining Ability and Their Genetic Basis of Yield among Key Parental Materials of soybean in Huang-Huai Valleys THE ANALYSIS OF COMBINING ABILITY IN WHEAT CULTIVARS FOR QUALITY AND AGRONOMIC CHARACTERS Study on Combining Ability and Heritability Analysis of Main Economic Characters for Cauliflower STUDIES ON RECURRENT SELECTION FOR SPECIFIC COMBINING ABILITY IN TWO MAIZE POPULATIONS