Combining Ability And Heterosis For Agronomic And Quality Characters Of Japonica Hybrid Rice (Oryza Sativa L.)

The combining ability and heterosis for the major agronomic and quality characters were studied with the BT-type CMS lines newly bred and restorer lines widely used by the NCâ…¡design. The main results were summerized as below.1. The combining ability for 13 agronomic characters was studied with 12 new BT-type japonica sterile lines and 8 restorer lines by NCâ…¡4 design. Both general combining ability (GCA) and specific combining ability (SCA) of all the characters were significant at 1% level except for the number of panicles per plant in which the SCA was insignificant. The GCA was more important than SCA in most characters. The SCA for number of filled grains of main panicle, seed setting rate, grain weight per plant and harvest index was greater compared to other characters. The other characters were influenced more greatly by restorer lines than by sterile lines, except panicle length, panicle neck length, seed setting rate and harvest index. GCA and SCA effects were independent each other. Hybrid japonica rice had stronger heterosis over mid-parent, but heterosis over parent and competitive heterosis of most characters were not strong. There was a significant positive relationship between the combining ability and heterosis. Based on the GCA and SCA of the parents, sterile lines Liuyan A, Danyang 941A, 98G26A, 99-9A, Xiangjing 8016A, 95122A and restorer lines C418, J16, Wan 161, C76 were recommendable.2. The combining ability and heterosis for 12 quality characters were studied with 9 new BT-type japonica sterile lines and 5 restorer lines by NCâ…¡design. General combining ability (GCA) variance of all characters was significant or highly significant. Except milled rice length and length/width ratio, specific combining ability (SCA) variance was significant or highly significant for other characters. Milled rice ratio, head rice ratio, tasted value and amylose content were controlled by both additive and non-additive effect, other characters were mainly controlled by additive effect. Grain shape and tasted quality characters were influenced by sterile lines and restorer lines, while milling quality and appearance quality characters were mainly influenced by restorer lines. Most quality characters of hybrids rice showed the measurements between their parents except milled rice ratio, head rice ratio and tasted value showed heterosis over parent. There was a significant or highly significant positive relationship between the combining ability and heterosis for most characters. Based on the GCA effect and SCA variances of the parents, sterile lines 95122A and Xiangjing 8016A and restorer lines J16 and R187 were recommendable and can be widely used for high quality breeding for japonica hybrid rice.3. The flowering habits of 7 BT-type CMS lines newly bred were studied. The results showed that the flourishing flowering of all sterile lines was later than that of C418. The opening angles of spikelets of all sterile lines were smaller. The stigmas could not exsert except 95122A and 99-12A with low stigma exsertion rate. The order of outcross seed setting percentage from big to small is Liuyan A, 99-12 A, Xiangjing 8016A, 95122A, Danyang 941 A, 99-9A, 98G26A.4. Genetic diversity among 30 Japonica rice was studied using the SSR molecular marker, and relationship between genetic distance based on SSR markers and yield heterosis was discussed. The materials consisted of 30 parents and 200 F₁ hybrids with a diallel crossing design. The results indicated that 64 SSR markers detected 185 alleles among 30 parents with 2.9 on the average. Polymorphic index content (PIC) values varied from 0.064 to 0.844 with an average of 0.380. Cluster analysis by UPGMA classified 30 parents in seven groups based on genetic similarity corresponding to the heterotic groups determined by their pedigree analysis. The correlations between the genetic distance and yield heterosis and hybrid performance were significant except total spikelets per panicle, but the values were too small(-0.361⁰.359) to predict heterosis. The research indicated that molecular markers could be used as a useful tool for assigning heterotic group and measuring genetic diversity. .