Studies on the Combining Ability of Agronomic Characters in Early-Seasoned Hybrid Rice

Sixty early-season hybrid rice combinations were made by the incomplete diallel design using 6 cytoplasmic male sterile lines and 10 restorer lines.The effects of combining ability for 12 agronomic characters of these combinations and their parents were analysed under the same conditions of cultivation.The results showed that the additive effects were predominant for the characters such as plant height,panicle length,effective panicle number,maximum tiller number, seed-bearing panicle percentage,plump or total seeds per panicle,seed set,1 000-grain weight,growth duration,expected and observed yields and that the general combining ability was not closely correlated with phenotypic value in the parents nor the specific combining ability in the combinations made,but significantly and positively correlated with over-standard heterosis of the combinations made.Therefore,it was suggested that the parents with high combining ability,superior and mutually complementary agronomic characters should be chosen in making combinations of early-season hybrid rice.