| Rice is one of the most important food crops in China.With the increasement of the population,the demand for rice continues growing.Rice sheath blight(SB),caused by Rhizoctonia solani Kuhn,is one of the most important diseases affecting rice production.Development of rice variety with resistance to SB is the most economical and effective approach to control the disease.In addition,development of salt-tolerant rice variety for plant in the area along the beach is an important approach to increase rice production.Both SB resistance and salt tolerance are quantitative traits and controlled by multiple genes.Identifying of new SB-resistant and salt-tolerant varieties and genes are of great significance.In this study,two sets of populations,one is mainly consisted of domestic varieties named Population I and the other is from different countries named Population II,were used to screen new SB-resistant and salt-tolerant varieties.Meanwhile,combined with high-density SNP genotype of each variety,genome-wide association studies(GWAS)were used to detect genes/QTLs associated with SB resistance,agronomic traits and salt tolerance.The main results are as follows:1.Some agronomic traits were measured for 175 cultivars in Population I,and the results showed that this Population has a certain genetic diversity.Through genome resequencing,about 200,000 valid SNP polymorphic markers,with an average inter-space of lL85 Kb,were obtained.Through GWAS,we detected 131,131,5,170,73 and 257 SNP markers significantly associated with panicle length(PL),grain length(GL),grain width(GW),grain length-to-width ratio(GLAV),plant height(PH)and heading date(HD),respectively.According to the distribution regions of these markers,12,5,1,11,8 and 11 QTLs associated with PL,GL,GW,GL/W,PH and HD were inferred,respectively.Most of these QTLs were found localized in previously cloned QTLs or genes or their neighbouring regions.Some new QTLs for these traits were detected in this study either.2.We evaluated the SB resistant phenotypes of 175 varieties in Population I and 5 control varieties using artificial inoculation in field as well as in growthcnamber using isolate stem.We found that both methods can effectively distinguish 5 control varieties into different resistant types as previously reported.Totally,we found 5 and 8 new SB-resistant germplasms from field and growthchamber conditions,respectively,and among them Gannong 3425 and Ewan 5 were the two varieties selected in both methods.Through GWAS,we detected 107,70 and 54 SNP markers associated with disease ratings(DR)in field,lesion length(LL)and relative lesion length(RLL)in growthchamber,respectively.According to the markers location,we determined 11,6 and 11 SB resistance QTLs associated with DR,LL and RLL,respectively.Compared with the previous reports,we found that 22 out of these QTLs located in or near the previous SB resistance QTLs,like qSB-11LE,qSB-2YSB,qSB-9TQ and so on.3.Salt tolerance of 229 cultivars in Population ? and 5 control cultivars was evaluated at booting stage in greenhouse,which resulted in 4 new rice germplasms(BR24,Palmyra,Eh la Chiu and Taducan)with stong salt tolerance.The relative panicle lengths and seed setting rates of the 4 germplasms after salt treatment were higher than those of the salt-tolerant controls,and the relative contents of Na+was similar as those of the three salt-tolerant controls.Through GWAS,we detected 60,123 and 15 SNP markers associated with the contents of Na+and K+,and the ratio of Na+/K+,respectively.According to position of each marker,15,20 and 3 salt-tolerant QTLs associated with the contents of Na+and K+,the ratio of Na+/K+were identified.Six of these QTL regions were found contain the known salt tolerance genes,like OsFH1?WAK32?VDAC2 and so on,and the remaining 32 loci were probably new QTLs for salt tolerance.The above results provide new genetic information and germplasms for molecular breeding towards SB-resistant and salt-tolerant varieties,which are of great significances in practice. |
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