Molecular Mapping Of Quantitative Trait Loci Using Recombinant Inbred Lines And Near-isogenic Introgression Lines In Rice(Oryza Sativa L.)

Quantitative trait loci (QTLs) underlying grain yield components and related traits segregating in 292 F13 recombinant inbred lines (RILs) derived from the rice cross of Lemont/Teqing were mapped using molecular markers and mixed linear mode approaches. To confirm and characterize the detected QTLs, a set of near iso- genic introgression lines (NIILs) in the Teqing (indica) background was constructed using Lemont (japonica) as the donor. The NIILs were genotyped with SSR markers and phenotyped for 14 traits of agronomic importance. The genetic constitution of the NIILs with regard to the donor genomic segments and distribution they contained and associated phenotypic changes were characterized and summarized as follows: 1. Genetic dissection of panicle number per plant, spikelet number per panicle and its related traits in rice The genetic mechanism underlying panicle number per plant (PN), spikelet number per panicle (SNP) and its components in rice was dissected using 292 F13 recombinant inbred lines (RILs) and a complete linkage map. The RILs showed tremendous transgressive segregation for all traits studied. SNP was largely determined by panicle branching number while panicle length traits contributed indirectly to SNP through their influences on panicle branching number. Fifty-one main-effect QTLs and 45 epistatic QTL pairs affecting these traits were identified and mapped to all 12 rice chromosomes. Collectively, these QTLs explained over 60% of the total variation of individual traits in the RILs. Most main-effect QTLs tended to affect more than one related trait, providing insights into the genetic basis of the trait correlation. Almost all SNP-QTLs were attributable to one or more of its contributing components. Branching number traits had greater contributions to SNP than length traits, in which the first had twice as many QTLs mapped in the same regions with SNP as the latter. Only two PN-QTLs were mapped in the near regions with the QTLs of those related traits of SNP, providing useful information for marker-aided 4 improvement of both PN and SNP. Some main-effect QTLs having large effects provided good candidates for marker-aided selection to improve the sink size. These included QPn4 for panicle number, QPbn3b, QPbn4 and QPb14 for panicle branching and length. 2. Genetic dissection of grain weight and its related traits in rice The genetic determinants affecting grain weight (GWT) and its 6 component traits (grain length, grain width, grain thickness, lengtblwidth, grain volume and grain density) in rice was dissected using the same RILs. The RILs showed tremendous transgressive segregation for all traits studied. GWT was positively correlated with all other grain traits. Significant negative associations existed between grain width, thickness, volume and grain density, which could be associated with grain quality. Forty-eight main-effect QTLs and 38 epistatic QTL pairs affecting these traits were identified, collectively explaining over 55% of the total variation of individual traits. Most QTLs affecting related grain traits tended to map to their genomic locations in clusters but in different locations from QTLs of SNP and its components, indicating pleiotropy was the primary genetic basis for the trait correlation and these two major components of the primary sink were genetically independent. QG13 had larger effect on GWT through increasing grain volume, at which the Lemont allele w...