Genetic Analysis And QTL Mapping Of Resistance To White-backed Planthopper In Guangxi Wild Rice Y11 And Indica Rice Variety IR13427-45-2MR-5

The white-backed planthopper（WBPH,Sogatella furcifera Horváth）belongs to the Delphacidae of Homoptera family and is one of the main pests in rice production.The white-backed planthopper mainly gathers at the base of the rice stalk,sucks the nutrients in the phloem through the needle stick,and secretes saliva to block the transduction tissue.In severe cases,the plant may fall down or even die,causing serious yield loss.In addition,the white-backed planthopper is also the main transmission vector of viral diseases such as Southern rice black-streaked dwarf virus（SRBSDV）,which seriously threatens rice production.The white-backed planthopper damages almost all rice-growing areas in China,and the average annual damage area in China exceeds 200 million acres of land.Because of its strong migratory habit,it has increased the difficulty of prevention and control.For a long time,the application of chemical pesticides has been the main measure to control the white-backed planthopper.However,the long-term excessive use of chemical pesticides not only pollutes the environment,destroys the ecological balance,increases production costs,but also promotes the development of resistance to the white-backed planthopper.New types of prevention and control are needed.Cultivating and promoting insect-resistant varieties is considered to be the most cost-effective and effective measure to control the white-backed planthopper.In the early stage,many scientific research institutions and researchers at home and abroad have made some achievements in the discovery of rice varieties resistant genes/QTLs to white-backed planthoppers through the screening of white-backed planthopper resistance sources.However,due to the high reproduction rate of the white-backed planthopper and the strong adaptability of resistant varieties,after the introduction of some resistant varieties previously bred,huge environmental pressure prompted the white-backed planthopper to accelerate the evolution process,resulting in the loss of resistance of the variety.Therefore,it is necessary to continuously discover new resistance genes and breed new rice varieties with long-lasting resistance to the white-backed planthopper through multi-gene aggregation.Preliminary research in the laboratory found that Guangxi wild rice Y11 from Guangxi Academy of Agricultural Sciences and indica rice variety IR13427-45-2MR-5 from International Rice Research Institute have certain resistance to white-backed planthopper.On this basis,this study completed the genetic analysis and QTL detection of the above-mentioned two varieties of white-backed planthopper resistance.The main results are as follows:1.Genetic analysis and QTL mapping of Guangxi wild rice Y11 resistance to white-backed planthopperThrough the rice seedling standard seedbox screening test,the resistance of Guangxi wild rice Y11 and Guanghui 998 was tested for white-backed planthopper resistance,and it was found that the death rate of Guanghui 998 seedlings was 96%,and that of Guangxi wild rice Y11 was only 26%.The above results indicate that Y11 is highly resistant to white-backed planthopper,while Guanghui 998 is highly susceptible.In the early stage,the Guangxi Academy of Agricultural Sciences constructed the Guangxi wild rice Y11/Guanghui998 BC₃F₈ genetic segregation population.This study completed the identification of the resistance of the 228 families of the genetic segregation population to the white-backed planthopper,and found that its resistance levels are continuously distributed,indicating that the white-backed planthopper resistance of Y11 may be controlled by multiple sites.Subsequently,226 pairs of KASP markers were used to construct a genome-wide genetic map with a total length of 1384.65 c M and an average genetic distance between markers of 6.13 c M.Inclusive composite interval mapping（ICIM）was used to detect the quantitative trait locus（QTL）of rice resistance to white-backed planthopper.Three QTLs were detected,located on the second,sixth and eleventh chromosome,and they were named q WBPH2,q WBPH6 and q WBPH11.The LOD values of the 3 QTLs were 4.8,2.5 and 3.7,respectively,which could explain the phenotypic variation of the population 9.3%,2.3%and 5.6%of the 3 QTLs.Among them,q WBPH2 is located in the second chromosome id2013634 and id2015636 marker 16.17 c M range,the additive effect is-0.2.q WBPH6 is located in the sixth chromosome id6006868 and id6007754 marker 7.39 c M range,the additive effect is-0.07.q WBPH11 is located in the eleventh chromosome id11005456 and K＿id11007840 marked the 18.53 c M interval,the additive effect was-0.17.According to the positive or negative additive effect,the resistance alleles of q WBPH2,q WBPH6 and q WBPH11 are from Guangxi wild rice Y11.2.Indica rice variety IR13427-45-2MR-5 resistance to white-backed planthopper genetic analysis and QTL mappingAfter group inoculation identification at the seedling stage,when the seedling death rate of japonica rice variety 02428 reached about 90%,the seedling death rate of indica rice variety IR13427-45-2MR-5 was about 42%,indicating that 02428 is highly susceptible,while IR13427-45-2MR-5 Medium resistance to white-backed planthopper.In order to analyze the genetic basis of IR13427-45-2MR-5 resistance to white-backed planthopper,this study used IR13427-45-2MR-5 and 02428 to construct an F₂ genetic segregation population,and completed 81 F_2:3 families of white-backed planthoppers.Identification of white-backed planthopper resistance and suitability test（χ²）showed that the white-backed planthopper resistance of IR13427-45-2MR-5 is a quantitative trait controlled by multiple genes.Using 179 pairs of KASP markers with polymorphism between IR13427-45-2MR-5and 02428,a genome-wide genetic map with a total length of 2051.65 c M and an average genetic distance between markers of 11.46 c M was constructed.The QTL for white-backed planthopper resistance was detected by the inclusive composite interval mapping（ICIM）method.As a result,two QTLs were detected on the third and twelfth chromosomes,which were named q WBPH3 and q WBPH12,and the LOD value was 3.7 And 2.9,respectively,can explain 11.1%and 14.2%of the population’s phenotypic variation.Among them,q WBPH3 is located in the 7.99 c M interval of the third chromosome id3008314 and id3009116 markers,the additive effect was 0.16;the q WBPH12 detected on the twelfth chromosome is located in the 20.63 c M interval of the two markers K＿id12007742 and K＿id12009549,the additive effect was 0.14.The discovery of the above-mentioned QTLs for white-backed planthopper resistance provides useful genetic resources and corresponding molecular markers for the breeding of resistant varieties through marker-assisted selection（MAS）,and is also a gene for white-backed planthopper resistance.The cloning and clarification of resistance mechanism laid the foundation.