Study On Inheritance And Correlation For Grain Yield And Quality Traits, QTL Mapping For Heat Tolerance And Molecular Marker-assisted Selection For Amylose Content In Rice

Now,cultivation of the good quality and new rice(Oryza sativa L.) hybrid combinations,which are insensitive to environment with high and steady yield,has been the most important goal for rice breeding.Improvement of heat tolerance of rice is getting more and more stringent,as seed setting rate decreasing remarkably caused by high temperature resulted in serious lost of rice yield in recent years.In this paper,in order to avoid influences from environment and interactive effect of environment and genotype,the inheritance of grain yield and quality traits,the correlation and the stability among these traits were studied systematically by utilization of the data come from the experiment in 4 ecological trial places representing different environment in Sichuan Province,and 24 diallel crossing combinations derived from 5 cytoplasm male sterile lines and 3 restorer lines of good rice quality besides zhenshan97A and Minghui63.Among the total,the research results of stability of the quality characters,correlation of the quality characters and other characters were reported for the first time,and the possible technical routes for breeding good quality hybrid rice combinations that are insensitive to environment with high and steady yields in our province were discussed.The genetic linkage map including 157 SSR markers was constructed with a recombinant inbred line(RIL) population consists of 168 lines from a cross of Oryza sativa indica Zhongyouzao No.8 and Oryza sativa japonica Fengjin,and the quantitative traits loci(QTL) analysis on heat tolerance in earing period was done by using composite interval graphic method and the difference of seed setting rate between normal and high temperature as heat resistance index.Three new heat tolerance QTLs were detected in the second,third,fifth linkage groups,respectively. According to the reported sequence difference between waxy gene Wx~a and Wx~b of non-glutinous rice,two pairs of dominant sequence tag site(STS) molecular markers were designed to distinguish Wx~a from Wx~b based on the special site between the two genotypes, moreover,the two markers were used for study on improving quality of cytoplasm male sterile line by marker-assisted selection method,and a high-quality sterile line passed the Province-level assessment,and 3 combinations participated in region test trials.The purpose for this study is to provide theoretical references and technical foundations for the breeding of the good quality and new hybrid combinations,which are insensitive to environment with the high and steady yield and the rice genetic improvement of heat resistance.The main findings are as follow:1.Genetic and correlation researches of yield and quality traits of hybrid rice1.1 The main reasons for less combination numbers(30.43%) and lower increasing range (0.66～4.05%) in grain yield than Shanyou63 were lower seed-setting rate of experimental combinations and lower general combining ability of cytoplasm male sterile lines. Comparing the national standard for good quality rice with the index of experimental combinations,the key problems were higher chalky grain rate bigger chalky degree and lower head rice rate.1.2 Genotype effect and trial effect of rice yield,grain length,grain width,ratio of grain length and width,chalky grain rate,chalky degree,brown rice rate,milling rice rate,head rice rate,amylose content,gel consistency and gelatinization temperature were significant at 1%level,the interactive effects between genotype and site for all traits except GT were significant at 1%level too,which implied that the genetic improvement and stability evaluation of rice yield and quality characters are both important.1.3 Both improvement of combination ability of parents and aplegamy of combinations have significant effects on higher yield and quality characters except gelatinization temperature.Improvement of restorer lines play the most important role in yield(62% relative importance),the next is combination of sterile lines(24%),evaluation and screening of combinations(14%).The sterile lines play the most important role in quality improvement,but relative importance is different for different rice breeding targets,and the strategies of rice improvements should be different too.1.4 Of all the quality characters,chalky grain rate and chalky degree were of lowest stability,head rice rate,gel consistency and amylose content were of lower stability,but grain length and width ratio,brown rice rate and other traits were of higher stability. Among 4 trial sites,there was the best discriminating ability for chalky grain rate and chalky degree in Yibin,amylose content in Nanchong,head rice rate and gelatinization temperature in Chengdu of Sichuan Province,respectively.1.5 The correlation analysis among rice quality characters indicates that it is hard to combine all the quality characters perfectly.There are facilitative significant or extremely significant correlations among appearance characters,processing and flavor characters;and to increase grain length or grain length and width ratio are good for the improvement of the appearance and flavor characters,but not good for promoting the head rice rate and milling rice rate.The increasing of amylose content is facilitative to the addition of the head rice rate.1.6 The correlation analysis between the rice yield character and quality character indicates that it is not easy to combine high quality and high yield.The main reason is that high yield needs more single-ear weight which is harm to the appearance quality but good to the head rice rate.The yield character constitution of ear number type is harm to the head rice rate but good to other quality character improvements.1.7 The correlation analysis between rice quality and its stability indicates that there is no significant correlation between stable index of single quality character and its phenotypic value,so it is possible to breed varieties of high-quality rice insensitive to environment. High chalky degree is harm to stability of the brown rice rate and milling rice rate,and promoting the stability of the chalky grain rate and chalky degree are positive to the head rice rate.The indirect selection of stability of low chalky grain rate and low chalky degree are important for the improvement of the appearance and processing characters.1.8 All of the correlation coefficient among rice yield,its stability and stability of every quality trait were not significant;which implied it was possible to combine high yield with stability of yield and the quality traits.2.QTL analysis of rice heat tolerance in heading period2.1 By composite interval mapping method of software windows QTL Cartographer 2.0,it was determined that three heat tolerance QTLs qhts-2,qhts-3 and qhts-5 with significant additive effects located in the second,third,fifth linkage groups respectively,the rang of contribution rate was from 6.59%to 10.72%,the co-contribution rate was 28.01%.The action manner for qhts-3 was mainly additive effect;qhts-2 and qhts-5 were mainly over-dominant effects.The heat tolerance QTL qhts-2 and qhts-5 detected in the second and fifth linkage groups were reported for the first time.The qhts-3 is a new QTL,which location is different from the only heat tolerance QTL previously reported between markers RZ892 and RG100 in the third linkage groups.2.2 The correlation between the Cheng's index and heat tolerance index,spikelet fertility of the RIL population under natural field and high temperature environment was not significant,repetitively,which implied that the RIL population of japonicalinous distribution didn't impact on QTL mapping.The extremely significant positive correlation between spikelet fertility under natural field and high temperature environment,and between heat tolerance index and spikelet fertility under natural field and high temperature environment respectively,but extremely significant negative correlation between rate of high temperature seed setting and the heat tolerance index,implied that it was very necessary for selection of heat tolerance material to be conducted under normal and high temperature environment.3.Molecular marker assisted selection of amylose content in rice3.1 Two sequence tag site(STS) dominant markers Wi10-1 and Wi10-2 specially identifying non- glutinous rice Wx allele genes Wx~b and Wx~a were constructed.3.2 The two molecular markers,the correlation coefficient between which and amylase content is up to 0.905,can accurately identify Wx~bWx~b and Wx~aWx~a.3.3 The designed two markers were used to breed cytoplasm male sterile line of hybrid rice by marker-assisted selection for Wx allele genes Wx~b during lower generation's period of maintainer and cytoplasm male sterile line.A new cytoplasm male sterile line Luxiang 618A with good quality was bred and has passed technical identification in Sichuan Province in 2006;moreover,three good quality combinations derived from Luxiang 618A have taken part in national or provincial rice region experiment.