Variation in quantitative characters and heterosis in F₁ rice (Oryza sativa L.) hybrids as affected by male sterile cytoplasm

In hybrid breeding programme based on cytoplasmic-genic male sterility, the effect of sterility inducing cytoplasm on agronomic traits is of considerable importance. In rice (Oryza sativa L.) there are reports showing that sterile cytoplasm reduced the productive capacity of hybrids compared with normal cytoplasm of the maintainers. Forty eight hybrid combinations including 24 AIR hybrids and their reciprocals were evaluated and mean values for 15 different characters were compared. It was found that there is significant difference between direct hybrids and their reciprocals for almost all characters except days to flowering, total dry matter production, panicle length and 100 seed weight. This difference in performance of these two sets of hybrids can be attributed to cytoplasmic effect. Even though these are the average performances of the two groups of hybrids, when different cross combinations are compared, it can be seen that these are cross specific and each cross differs in their performance. Evaluation of heterosis expressed by different hybrids revealed that number of reciprocal hybrids expressing positive and significant heterosis for grain yield was high compared to direct hybrids. All these explain the possible negative influence of sterile cytoplasm on quantitative characters.