A Primary Study On The Genetic Basis Of Grain Shape-Related Traits Through Chromosome Segment Substitution Lines In Rice (Oryza Sativa L.)

Rice (Oryza sativa L.) is one of the major food crops in Asia and even the whole world. However it will be a big challenge for breeders to improve the yield and quality of rice at the same time, because the yield and quality traits are usually negative correlation. Grain shape-related trait is one of the main breeding characters in rice, and it not only affects the yield but also affects quality of rice. Although researchers have done extensive research to study the genetic mechanism of grain shape over the past decade. However, the genetic basis of rice grain shape trait remains unclear. Therefore, it will be important to demonstrate genetic basis for high yield and good quality in rice breeding.In this study, we use two sets of CSSLs which derived from a japonica cultivar Asominori and an indica cultivar IR24 and the F1 populations which backcross with the recipient parents. The genotypes of the CSSLs were made up SSR markers. Combining with grain shape phenotypic data, we analysed additive-dominant QTL loci using the Icimapping software in four environments. At the same time, we detected heterotic loci affecting grain shape traits in F1 populations. The main conclusions are as following:1. SSR genotype map construction:The genotype of the NAIS and NIAS CSSLs are build by 131 pairs and 126 pairs of SSR markers, respectively. In the NAIS,9% family are SSSL,50% family contains from 2 to 3 donor segments,8% family contains from 4 to 5 donor segments,9% family contains more than 6 donor segments. Overlapping fragments accumulated up to 211; in average each family contains 3.29 donor segments. Each fragment is repeated in 1.61 family. In the NIAS,15% family are SSSL,49% family contains from 2 to 4 donor segments,21% family contains from 5 to 6 donor segments, 12% family contains more than 7 donor segments. Overlapping fragments accumulated up to 209; in average each family contains 3.66 donor segments. Each fragment is repeated in 1.65 family.2. Phenotypic variation of grain shape traits are as following:the grain width and length-width ratio of NAIS have no obvious difference in two environments except grain length and grain size. It show that japonica varieties are more suitable to grow under the condition of long sunshine.The grain shape traits of NIAS show better in E2. They are expressed in moderate LWR and larger Grain size. It shows that indica varieties are more suitable to grow in the more rain and fertile area. From the whole phenotype of CSSLs, there is little difference comparing with the background parents. While from the single family, transgressive segregation is obvious.3. With the data of grain shape, we use the QTL-Icimapping software to test the additive-dominance QTL in 4 groups. We detected 3 additive-dominant QTLs which influenced GL in NAIS and NAISF1. qGL2-1-I has both additive and dominant effect, but the other 2 loci just have additive or dominant effect.6 additive-dominant QTLs influenced GW. qGWl-1-I has both additive and dominant effect in Guiyang environment. 6 additive-dominant QTLs influenced LWR. qLWRl-1-I has both additive and dominant effect in two environments.4 additive-dominant QTLs influenced GS, but just have additive or dominant effect. We detected 2 additive-dominant QTLs which influenced GL in NIAS and NIASF1. qGL3-1-A and qGL4-1-A have both additive and dominant effect in Guiyang environment. However, qGL3-1-A shows additive QTL, and qGL4-1-A shows dominant QTL in Nanjing environment, respectively.5 additive-dominant QTLs influenced GW. qGW2-1-A has both additive and dominant effect in Nanjing.4 additive-dominant QTLs influenced LWR. qLWR3-1-A and qLWR5-1-A have both additive and dominant effect in two environments.2 additive-dominant QTLs influenced GS, but just have additive or dominant effect.4. Calculating the value of Hmp and combining genotype data in two environments, we test the heterosis loci in F1 group. In japonica, we detected 1 HL associated with grain length which nears RM411 has obvious advantage.1 HL associated with grain width nears RM493.2 HL associated with length-width ratio which near RM411 and RM493. In indica background, we detected 1 HL associated with grain length which nears RM3467.1HL associated with LWR nears RM3467. But there is no stable HL about GW and GS.5. For these additive-dominance QTL loci, we analyse the genetic basis of the grain shape traits by calculating the average degree of |D/A|. The results show that in japonica background the genetic basis of GL is mainly additive effect, while over-dominant and part dominant are the main genetic basis for grain width. The genetic basis of length-width ratio is mainly part dominant. While dominant effect is the main genetic basis of grain size. In indica background, part dominant is the main genetic basis of grain length, grain width and length-width ratio. Dominant effect is the main genetic basis of grain size.6、From the distribution of additive and dominant QTL on chromosome, these QTLs are mainly distributed on chromosome 1,2,3,4,5,6,10,12 and prevalently have pleiotropism effects. So it is possible that the pleiotropic QTL may be one of the genetic basis of grain shape-related traits.