Genetic Analysis And Validation Of The Quantitative Resistance And Its Related Traits Of Rice To The Stem Borer

Rice stem borers (RSB) such as the striped stem borer (Chilo suppressalis (Walker)) (Lepidoptera:Pyralidae) are destructive and widespread insect pests throughout the rice growing regions in Asia. The genetic mechanism of the RSB resistance is complex, and not to be understood now. The aims of research in the dissertation were to analyze the quantitative trait of rice resistance to the rice stem borers (RSB), detect related quantitative trait loci (QTLs), and explain the resistance element of the genetic population. The results will be significance for RSB resistance molecular breeding in the future.The genetic population adopted involving 154 doubled-haploid lines of a population derived from a cross between CT9993 (RSB susceptible tropical Japonica breeding line) and IR62266 (moderately resistant indica rice culture). All the doubled-haploid lines were screened to assess their levels of resistance to RSB by measuring the dead heart (DH) and white head (WH) on different days after sowing (DAS) (40 DAS,55 DAS,70 DAS,85 DAS,100 DAS respectively). A mixed-model-based composite interval mapping method (MCIM) was performed to identify QTLs for RSB tolerance.Next, we selected three main effect QTLs of RSB resistance which also related to PH or TN, and constructed near-isogenic lines (NILs) which the chromosome position of these QTLs were isolated by using marker associated selection (MAS) method. Three SSR markers RM102, RM210, RM219 separate adjacent to three QTLs and several chromosome segment substitution lines in the population lines were selected out for the experiment. The NILs would be used to study the isolation genetic effects of these QTLs as a single Mendelian factor. Afterward, the NILs were employed to verify primarily the isolation QTLs genetic effect in the field expression. In the two growing season experiments, the PH, TN, RSB resistance and other traits was investigated, and rice stem infested with the striped stem borer (SSB) larvae in laboratory experiment to evaluate the stem resistance to SSB infestion.The results showed that the majority of the favorable resistant alleles with additive effects came from the resistance parent IR62266. Four major QTLs, the qSBR-1-35, qSBR-3-28, qSBR-8-24 and qSBR-9-7 were detected on chromosome 1,3, 8 and 9 respectively, which considered to be valuable for further resistance breeding programs. The epistasis analysis indicated that about half of QTLs from CT9993 have positive epistasis effects for the RSB resistance. As the prediction of genetic effects, the study will be contributed to the rice breeding program for RSB resistance.Since the previous studies indicated that the RSB resistance were correlated to rice phenotype such as plant height (PH) and tiller number (TN), advanced research was conducted to analyse the genetic effects between RSB resistance and PH/TN, and map the QTLs of PH and TN. The results showed that the genetic effects correlation coefficients between RSB resistance and PH/TN were extremely significant; it could be assumed that such RSB resistance-related genes must be related to PH/TN. Further more, some QTLs of PH/TN were mapped on the same location as those QTLs of RSB resistance. For example, the chromosome regions near the molecular marker RZ698 and EM11₁1 detected simultaneously influencing the PH and resistance, and regions near EM14₁, BCD855, RG476 and EM11₁1 were also detected to influence the PH and resistance simultaneously. It conferred one gene was located on these QTLs which had different genetic effects on PH/TN and RSB resistance.By using the NILs, we verified the QTLs genetic effects. The results showed that the chromosome segment of qtl-1-35 substitution NILs had significant difference in PH trait, then the qtl-8-24 substitution NILs had significant difference in TN trait. The results were consistent to the presumed QTLs genetic effects. Concurrently, it makes sure the SSR markers'efficiency in the MAS of the target QTLs.Finally, conditional QTL mapping of RSB resistance, PH and TN at different DAS indicated that the related genes (QTLs) expressed differently in different periods of traits dynamic development. The main effect QTLs qtl-8-25 and qtl-9-7 showed significant genetic effects of RSB resistance before 55 DAS. QTL qtl-8-25 affected TN in early stage of rice growth and QTL qtl-9-7 played oppositively genetic effects on PH between 55 DAS and 70-85 DAS of rice growth. While QTL qtl-1-35 which expressed from 55 DAS to 70 DAS significantly affected the PH. Based on the uncondition QTL mapping results before, the genetic mechanism of the RSB resistance main effect QTLs at the molecular level was advanced analysised.