GSR Lines Evaluation At Vietnam And Joint Mapping Of Leaf-rolling Trait In Rice(Oryza Sativa L.)

Rice is the main food of billions of people around the world and the global demand for rice is still increasing.As one of the most important crops,it has been grown in the arable lands of 140.49 million hectares and produced 667.93 million tons in Asia,accounting for 90.15% of world rice output.However,rice has also been a crop commonly request more input to maintain satisfying grain yield.This condition has now been changed by a project named Green Super Rice(GSR)Project chaired by CAAS in coorperating with IRRI aiming at the development of GSR varieties for adaptation to climate change and achieve grain yield with less input.This research contains two major parts,including: 1)evaluate GSR advanced backcross lines(BILs)and identify suitable elite lines for Vietnam,2)jointly analysis with BILs together with RILs as well as the germplasms collected by GSR projects for leaf rolling traits which may contribute to the future improvement of GSR in a population scale.Major conclusions were listed as following:1.Result of the Green Super Rice research projects in Vietnam in the period 2012-2017 has been very successful.Some elite lines were identified to be suitable for Vietnam.Based on three tests of 12 rice lines(result from screening of 754 imported GSR BILs)across three rice crop seasons at two locations in Phu Yen Province,four promising GSR lines were finally identified,namely GSR65,GSR90,Nam Uu 1245 and GSR38.Results of trials production and demonstration model of two GSR lines(GSR65,GSR90)in Phu Yen Province have further shown that the GSR lines,GSR65 and GSR90 reached the realized grain yield of 7.98 and 8.17 ton/ha,with 11.9% and 14.6% higher in comparing to the local control ML48(7.13 ton/ha).Cultivating techniques for GSR65 and GSR90 have also been developed.2.The leaf rolling(V-shaped or curled)trait has long been considered by experienced breeders to be a key trait for ideal plant type not only in Xian(indica)hybrid rice breeding but also in Geng(japonica)inbred breeding.Leaf rolling traits may futher help in GSR breeding with less input by both improving the photosynthesis,water-use efficiency,and micro-environment associated to disease resistances in a population scale.Thus,a preliminary joint-analysis was further carried out for this trait.Linkage mapping using a set of 262 highly variable RILs together with supporting evidences from BILs from two cultivars(Minghui 63 and 02428)with minor differences in leaf rolling index(LRI)was performed together with GWAS mapping with a random subset from the 3K Rice Genomes Project(3K RGP).Allele mining with representative SNPs and identification of the elite germplasm for the improvement of leaf rolling trait were also performed.Most favorable alleles at the detected loci were found to be contributed by various 3K RGP germplasms.By a re-scanning of the candidate region with more saturated SNP markers,we dissected the region harboring g Rl4-2 into three subregions,in which the average effect on LRI was 3.5% with a range from 2.4 to 4.1% in the third subregion,suggesting the presence of a new locus or loci within this region.The representative SNPs for favorable alleles in the reliable QTLs which were consistently identified in both linkage mapping and GWAS,including q Rl4,q Rl5,q Rl6,q Rl7 a,and q Rl7 b will be useful for future molecular breeding programs for ideal plant type improvement for our next generation of GSR.In a word,this research has not only identified elite lines from GSR BILs for Vietnam,but also make a technique stock for the future GSR improvement in a population scale by a joint analysis with the RIL together with BIL as well as GSR project germplasm collections.