Mapping Of QTLs For Resistance To Rice Black-streaked Dwarf Disease

Rice is one of the most important grain crops around the world.High yield and stable yield of rice is the livelihood problem of people all over the world.But,the production of rice is seriously affected by diseases and insect pests,which is an urgent problem to be solved.Rice black-streaked dwarf disease is a viral disease of rice transmitted by the small brown planthopper.Once rice black-streaked dwarf disease reach epidemic proportions,the tremendous yield losses will be occurred.It is the most effective method to breed the resistant varieties to control RBSDV.To develop resistant varieties,it is important to screen germplasm that shows RBSDV resistance and to identify the genes/quantitative trait loci(QTLs)underlying.However,the RBSDV resistance is controlled by quantitative trait locus(QTL),and no completely RBSDV-immune germplasm is currently available.Studies on RBSDV disease are characterized by procedural difficulties that include complex epidemic factors,the need for large-scale surveys,and a prolonged research cycle,which make the systematic and in-depth investigation of RBSDV a great challenge.There have been very few studies on the inheritance or breeding strategies associated with RBSDV resistance.Therefore,there is an urgent need to identify highly resistant resources to map QTLs for breeding resistance cultivars in order to reduce the damage caused by RBSDVD.In this study,222 recombinant inbred lines(RILs)which were developed from the cross between ER36 and L5494 and 140 chromosome segment substitution lines(CSSLs)by using Wuyujing 3 as recurrent parent and Dular as donor parent were used to locate the quantitative trait locus(QTL)for RBSDV resistance,and a near isogenic line that harbors qRBSDV-lIR36 derived from 93-11 in the Nipponbare(O.sativa spp.japonic'a)genetic background was used to detect the RBSDV-resistant QTL from 93-11(O.sativa spp.indica)at the qRBSDV-1IR36 locus.The main results are as follows:(1)A set of 222 recombinant inbred lines(RILs)derived from the cross between L5494(a susceptible japonica variety)and IR36(a resistant indica variety)had been constructed for RBSDV-resistant QTL mapping.With natural infection test,the RBSDV incidences of L5494 and IR36 were 84.26%and 28.70%.The disease incidence of RILs was ranged from 11.21%to 89.81%.A total of 134 molecular markers with obvious polymorphism between IR36 and L5494 were analyzed in 222 recombinant inbred lines,and a linkage genetic map was constructed.The map covered a total length of 1475.97 cM with an average interval of 11.1 cM between adjacent markers.Four RBSDV-resistant QTLs were discovered using IciMapping 4.0 Software,three of which,qRBSDV-1IR36,qRBSDV-2IR36 and qRBSDV-9IR36,were from the resistant parent ER36,and one,qRBSDV-615494,was from the susceptible parent L5494.qRBSDV-1IR36,qRBSDV-2IR36,qRBSDV-6L5494 and qRBSDV-9IR36 locate on chromosome 1,2,6 and 9,which explained 12.64%,16.00%,10.82%and 8.43%of the phenotypic variations.(2)N9,a near isogenic line that harbors the qRBSDV-1IR36 derived from 9311 in the Nipponbare genetic background,was used in 2017 and 2018.The incidences of N9 were significantly lower than Nipponbare in both two years,from which a RBSDV-resistant QTL from 93-11(O.sativa spp.indica)at the qRBSDV-1IR36 locus was confirmed.(3)To improve the resistance of Wuyujing 3 to rice stripe virus disease,we developed a set of backcross introgression lines in former study.Among these lines,T1012 showed high resistance to rice black-streaked dwarf viral disease.152 polymorphic molecular markers were used to detect the introgresed segments in T1012.Seven introgressed segments were detected on chromosome 1,3,4,5,7,10 and 11.With marker-assisted selection and backcross,a total of 140 CSSLs were constructed from the cross between T1012 and Wuyujing3.(4)Using a field test,the incidence of T1012 was 19.4%in 2016,and the incidences of Wuyujing3 were 37.0%and 41.4%in 2016 and 2017,respectively.The incidences of CSSLs were ranged from 16.7%to 80.0%and from 10.8%to 81.7%in both years,indicating that the resistance of T1012 to RBSDV was controlled by quantitative trait loci.Two resistant QTLs,qRBSDV-1 T1012 and qRBSDV-4T1012 on chromosome 1 and chromosome 4,were detected in 2016,which explained 8.85%and 14.16%of the phenotypic variations.In 2017,qRBSDV-4T1012 on chromosome 4 was detected and explained 9.28%of the phenotypic variations.All these QTLs were from the resistant parent T1012.(5)In 2018,thirteen lines harboring the different sizes of introgressed segments on chromosome 4 were selected from the CSSLs population to inoculate with natural infection.By analyzing the incidences of these lines,two linked QTLs,named qRBSDV-4-1T1012 and qRBSDV-4-2T1012,were found to locate in the interval of 0-1.87Mb and 2.02Mb-4.44Mb,respectively,on chromosome 4.