| Rice blast caused by the fungus Magnaporthe oryzae is one of the most devastating rice diseases worldwide,and cause high yield losses.Planting Rice varieties with genetic resistance is the most efficient and economical way to reduce yield losses from this disease.The AVR genes in M.oryzae are known to be highly unstable,and resistance based on a single R gene can be easily overcome shortly after its deployment,suggesting an urgent need to stack major blast R genes for adequate and relatively durable resistance in varieties.Pi-ta and Pi-b were the first two blast resistance(R)genes cloned with a wide resistance spectrum.In this study,on one side,a recombinant inbred lines(RILs)population of Cybonnetx Saber(CS)were inoculated by 4 races(10 isolates),and rice balst resistance QTL were mapped and their effect including Pi-ta and Pi-b were assessed.On the other side,yield related traits were evaluated in a two-year field experiments,and their QTL were mapped.Futher more,the correlation between Pi-ta,Pi-b and the yield related traits,their QTL were also analyzed.The results were summaried as the followings:1.It was demonstrated that rice seedlings from V1 to V4 stages were very susceptible by synchronous inoculation and separating stages inoculation with M-202 and Nipponbare.Due to the leaf areas in V3 to V4 stages are larger and the the disease leisions are more visible and recorded than the V1 to V4 stage,so rice seedlings in V3 to V4 are the most suitable stages for inoculation.After the V5 stage,adult plant resistance(APR)will be enhanced and meanwhile their susceptibility was reduced,and no visible symptoms were found when inoculation was done at V9 to V10 stages.2.A linkage map for the CS-RILs was constructed using 179 polymorphic SNP markers.And 6 rice blast resistance QTLs were mapped including two major resistance genes Pi-ta and Pi-b,four minor resistant QTLs,TBR3,qBR8,qBR9,qBRll,which were located at chromosome 3,8,9,11,respectively.Nine yield related traits QTLs were also mapped,five of them were 1000 grain weight QTLs,TGW3,qTGW2,qTGWl,qTGWl1,qTGW12 accounting for 26.62%,12.40%,13.13%,7.10%,and 4.29%phenotypic variation(PVE)respectively;two of them were panicle length QTLs qPL3,qPL1 with a PVE of 12.94%and 11.13%,respectively;and the other two of them were Panicle weight QTLs qPW2 qPW3 with a PVE of 8.09%and 6.64%,respectively.Of them,qPW2 is a new QTL.3.Additive to additive epistatic interaction between Pi-ta and Pi-b was detected.The mean additive effect of Pi-ta were 6.30%(0-100%)indicating that Pi-ta may reduce the disease area by 6.30%,and accounted for 38.65%phenotypic variation.The mean additive effect of Pi-b were 5.29%(0-100%)and accounted for 23.93%phenotypic variation.The additive to additive epistatic effect between Pi-ta and Pi-b was 5.05%(0-100%)indicating that they can decrease the disease by an additional 5.05%of disease area,they can account for an additional 17.77%of the phenotypic variation for the disease resistance in this population.Besides,The additive to additive epistatic interation between major resistant gene Pi-b and minor QTL qBR9,Pi-ta and qBR9,Pi-b and qBR3,Pi-ta,Pi-b and qBR8,were also detected.A total of 30 recombinant inbred lines with blast resistance QTLs were selected for breeding via a marker assisted selection(MAS)approach.4.The correlation between Pi-ta and Pi-b and 1000-grain weight was low in Cybonnetx Saber mapping populations 2016.And the correlation was also low betwee this two major resistance genes and the 1000-grain weight,panicle weight,panicle length and branch number.Some resistant RILs with high yield were excavated thanks to the low correlation btween Pi-ta,Pi-b and the yield related traits,which will provid the elite resouces of breeding for resistace and high yied. |
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