Genetic Mechanism Of Heterosis For Rice Milling And Appearance Quality In An Elite Rice Hybrid

Developing high yield and good quality hybrid rice is the need of food security and people’s living standards.The genetic mechanisms of heterosis for rice yield and its components have been extensively studied,but there are few studies on heterosis of grain quality traits.In this study,in order to understand genetic mechanism of heterosis for rice milling quality（brown rice rate,milled rice rate,and head milled rice rate）,appearance quality（degree of endosperm chalkiness and percentage of grains with chalkiness）and grain yield per plant in xian rice,QTL mapping was conducted using 1,061 recombinant inbred lines（RILs）derived from a cross of xian rice varieties Quan9311B（Q9311B）and Wu-shan-si-miao（WSSM）,and backcross F₁ population（BC₁F₁s）developed by crossing the RILs with Quan9311A（Q9311A）as experiment materials to analyze the phenotype and mid-parent heterosis in Hefei and Nanning environments.The haplotypes of all candidate genes in important QTL intervals were analyzed by 732 accessions from 3K materials,the candidate genes related to rice quality traits were predicted,and the genetic basis of rice quality heterosis was revealed.The main results were as follows:1.In the two environments,the RILs and BC₁F₁s had wide segregations in milling and appearance quality traits,and Quan-you-si-miao（QYSM）showing various degrees of heterosis for milling and appearance quality.The BC₁F₁s had relatively smaller heterosis for milling and appearance quality compared with QYSM.2.A total of 142 different main QTL（M-QTL）were identified for grain milling and appearance quality and grain yield per plant of the RILs and BC₁F₁s and corresponding mid-parent heterosis in Hefei and Nanning by constructing genetic linkage map.Among them30 M-QTL were commonly identified in both environments.Most additive loci detected in the RILs didn?t have heterotic effects but some of them did contribute to the performance of BC₁F₁s.3.A total of 198,119 and 90 epistatic QTL（E-QTL）were identified in RILs,BC₁F₁s and corresponding mid-parent heterosis,respectively,and epitasis had more contributions to the milling quality traits with heterotic effect than the appearance quality and yield traits.The heterosis of yield was mainly determined by single-locus overdominance,while the heterosis of rice milling and appearance quality was mainly determined by single-locus overdominance and epistasis.4.A total of seven QTL regions were identified on chromosomes 1,2,4,5,8 and 10,which simultaneously affected several traits of yield,milling and appearance quality in the same environment.Among them,three（four）QTL regions harboring opposite（consistent）directions of favorable allele effects for yield and grain quality were identified,which probably demonstrated the existence of partial genetic overlaps between yield and grain quality.5.Among the 24 M-QTL affecting five milling and appearance quality detected simultaneously in the two environments,seven heterotic M-QTL were selected for candidate gene analysis.Total of 14 candidate genes for the seven M-QTL were identified based on haplotype analyses,and performances of the haplotypes were characterized in xian and geng populations,combined with the bioinformatics function of the candidate genes,we discussed the most likely candidate genes.