Fine Mapping Of QTLs QWBPH3.2 And QWBPH11 Conferring The Resistance To Whitebacked Planthopper In Rice

Whitebacked planthopper(WBPH,Sogatella furcifera Horváth)is a kind of seasonal migratory pest,which belongs to Delphacidae of Homoptera.It mainly accumulates at the lower part of rice(Oryza sativa L.)plants and damages rice by sucking nutrients from the phloem.When WBPH attacks crops in large quantities,it will cause necrosis of rice basal tissues,lodge or death of the plants and great loss of the yield.WBPH is a serious threat to rice production,which not only causes mechanical damage to plants by feeding or laying eggs,but also transmits the southern rice black-streaked dwarf virus(SRBSDV).Because WBPH has a wide range of hosts and migrates seasonally,the management for this pest is difficult.For a long time,farmers rely on pesticides to control WBPH infestation.However,the excessive application of pesticides pollutes environment,kills natural enemies,and causes drug resistance of pests,which reduce the efficiency of pesticides,increase the dosage and form a vicious cycle.Rice resistance to WBPH is one of the most effective measures for the comprehensive control of insect pests.It can inhibit the growth,development and reproduction of pests,and does not increase the farmers cost of rice production.Based on the screening of resistant rice sources against WBPH,researchers have made some achievements in breeding new rice cultivars and mechanisms under insect resistance.Moreover,some WBPH-resistant genes or quantitative trait loci have been identified.As the reproduction rate of WBPH is very high,the selection pressure may speed up the evolution of the population.Therefore,it is necessary to excavate new resistant sources continuously and develop resistant rice cultivars for renewal.So far,only one gene has been fine mapped and no gene has been cloned.The molecular mechanism of rice resistance to WBPH is still poorly understood.Therefore,it is urgent to fine-map and clone rice WBPH-resistant genes for elucidating the molecular mechanism of rice resistance to WBPH.Therefore,we screened the resistance of 24 rice resources to WBPH in this study.It was found that IR54751-2-44-15-24-2(abbreviated as IR54751)was highly resistant to WBPH.In further study,IR54751 and the F1 derived from IR54751/02428 were resistant to WBPH at tillering stages.In resistance mechanism study,IR54751 showed stronger antixenosis and tolerance against WBPH than susceptible cultivar 02428.There was no difference between IR54751 and 02428 in antibiosis.In summary,the WBPH resistance of IR54751 is contributed by antixenosis and tolerance.In this study,an F2 population was constructed from a cross between IR54751 and japonica rice 02428.It was found that WBPH resistance levels of 118 F2:3 lines showed a normal distribution.Therefore,the resistance of IR54751 to WBPH was controlled by multiple quantitative trait loci(QTLs).The genetic map of IR54751/02428 F2 population containing 118 individuals was constructed by using 127 molecular markers with polymorphism between two parents.The markers were distributed evenly on the chromosomes of rice,and the map genetic distance was 1504.12 cM totally.Based on this map,we detected 4 WBPH resistance QTLs using the software QTL IciMapping 4.1.They are qWBPH3.1,qWBPH3.2,qWBPHll and qWBPH12 respectively,with LOD values of 3.8,8.2,5.8 and 3.9 respectively,accounting for 8.2,21.5,13.9 and 10.4%of the phenotypic variation.Their additive effects were 0.66,-1.51,-1.25 and-0.95 respectively.In conclusion,the resistance allele at qWBPH3.1 locus comes from 02428,while the resistance alleles at q WBPH3.2,q WBPH11 and q WBPH12 come from IR54751.In order to fine map qWBPH3.2,we constructed BC1F2 and BC2F2 population through the backcrossing of 02428 and the lines containing q WBPH3.2 resistance allele,selected by linkage markers.We found 74 recombinant lines from the population,using markers InDel3-17 and C3-2265.By identifying WBPH resistance level of the recombinant progenies,we delimited qWBPH3.2 in an 134-kb region flanked by C3-2220 and C3-2233.Besides,the individuals containing heterozygous q WBPH11 locus in F2 population was selected to construct F3 population.Totally,22 recombinant lines were screened from 1270 lines with the molecular markers linked with qWBPH11.Through the resistance identification of recombinant progenies and development of internal markers,we located the qWBPH1l at a 450-kb interval between DJ53973 and SNP56 on chromosome 11.The discovery of above resistance resources and the mapping of QTLs for WBPH provide useful genetic resources for the breeding of new WBPH-resistant rice cultivars.Fine mapping of the two QTLs qWBPH3.2 and qWBPH11,conferring resistance against WBPH,lays the foundation for cloning resistance genes and elucidating resistance mechanism in rice.