| Rice blast caused by Pyricularia grisea is one of the most destructive and widespread diseases in most rice growing regions of world, for which the rice breeding based on the heridity of host resistance has been the most economical and effective control measure. But new resistant cultivars usually become susceptible to the new predominant pathogenic races (groups) after 3 - 5 years of cultivation. So genetic studies on blast resistance in rice are great importance. This paper investigated the heterosis of hybrid rice in resistance to leaf blast by the conventional methods; gene effect by the augmented NC II design; combining ability and inheritability in resistance to leaf blast and neck blast by incomplete diallel methods, during seedling and adult stages respectively. The major results are as follows: 1. Genetic analysis of the leaf blast resistance of hybrid riceFor 7 CMS lines,7 restorers and 7x7 incomplete diallel crosses, the resistance to leaf blast was evaluated by inoculating with the mixed spore liquid of 37 pathogenic races of 7 groups during seedling stage and by setting up infector row in blast zone during adult stage. Heterosis, combining ability, inheritability and gene effect of resistance to leaf blast in hybrid rice were analyzed by four indices (disease plant rate, area of leaf lesion, the index of spore layer scales of lesions and disease index).The heterosis analysis results suggested that the resistance of hybrid rice to leaf blast during both seedling and adult stage had a strong heterosis, and a considerable variation among the crosses. On mean heterosis, the average values of the resistance during seedling and adult stage were among -41.30%~-20.24%, -39.65%--28.76%, respectively, and 63.27%-77.55%, 53.06%-75.51% of the 49 tested crosses had negative heterosis. On heterosis over the better parent, the average values were all above 0, but 14.29%-24.45% and 32.65%-42.86% of the 49 crosses had negative heterosis. The range of heterosis over the better parent during the 2 stage were all great, respectively among -100%-811.78%, -100%-1999.55%. The ranges of mean heterosis were relatively less, with the values of -100%-213.22% and -100%-186.29%.The combining ability analysis results suggested that the resistance of hybrid rice to leaf blast during both seedling and adult stages were controlled by additive and non-additive heredity components, but additive heredity component was predominant. The additive heredity component of the restorers was more important than that of the CMS lines, but the latter had significant effect on the resistance of its cross progeny FI. Having better GCA of resistance to leaf blast during both seedling and adult stage than the other tested parents had, 2 CMS lines (K42A,K40A) and 2 restorers( DuoHui No.l,Chenghui 149 ) had greater utilization potential. Having better GCA and bigger variance of SCA of resistance to leaf blast during adult stage, Jinhui No. 1 could be^ 2002utilized as excellent parent in the resistance breeding.The heritability analysis results indicated that the heritability of resistance to leaf blast during both seedling and adult stage of hybrid rice were very high, and basically consistent. The general heritability (h2B) were among 86.29%~96.48%, 88.04%~ 91.23%, respectively. The narrow heritability (h2N) were respectively among 52.40%~ 68.16%, 53.79%~66.25%. The h2N value was bigger than the h2B-h2N during each stage, which showed that the resistance to leaf blast during both stages of hybrid rice was controlled by additive and non-additive heredity components, but additive heredity component was predominant. The result was consistent to that of combining ability analysis.The resistance gene effect analysis was conducted by the methods of the augmented NCII design and hereditary model test proposed by Mo Huidong et al. in 1991. Covariance analyses and variance analyses of Wr+Vr and Wr-Vr indicated that the resistance heredity of hybrid rice to leaf blast during both seedling and adult stage was inconsistent to additive-dom...
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