| Drought is one of the global disastrous abiotic stress,which causes huge losses to agricultural production every year.In China,maize has the largest planting area among main planting crops(rice,wheat,potato,soybean,et al.),which was affected severely by drought stress.In addition,because maize germplasm bases in China is relatively narrow,it is of great significance to cultivate and improve new varieties of drought-tolerant maize.In this study,two recombinant inbred lines(RIL)populations,designated as C5 and C6,were subjected to drought stress at seedling stage,screened out drought tolerant materials and detected quantitative trait locus(QTL)affecting drought tolerance-related traits(plant growth amount,relative chlorophyll content,fresh/dry weight,plant relatively water content and leaves motality under drought stress),by inclusive composite interval mapping method.The Genotyping-by-Sequencing(GBS)technique was used to perform genotyping for two RIL populations,and high-density genetic maps were constructed for QTL mapping.The main results are as follows:(1)The drought resistance pot experiment was carried out at seedling stage at two experimental locations(Fenjiang and Duoying from in Ya'an)in 2016.The relative chlorophyll content,growth amount,fresh weight,dry weight,plant relative water content and leaves mortality of each recombinant inbred line were measured after 40 days of well water and water stress management.The variance analysis,heritability estimation,correlation analysis and principal component analysis(PCA)of each phenotypic data were carried out.Significantly difference were observed for all the traits between under well water and water stress conditions,which indicating that the measured criterias can well reflect the differences of plant growth under well water and water stress conditions.Relative high heritabilitics(0.61-0.92)was found for all the traits and significant correlation among most of the traits were observed.According to the principal component analysis,it was also found that the cumulative contribution ratios of the first three PCs for C5 and C6 were both more than 85%,where the plant relative water content played positively role in the first PC but the leaves mortality did negetively.(2)The drought tolerance of the two RIL populations was evaluated by comprehensive drought tolerance index(D value).Compared the mean and coefficient of variation of the D values among the two RIL populations at two experimental locations,it was found that the drought tolerance of C5 RIL population was stronger than that of C6 RIL population,and the overall drought tolerance of C5 RIL population was more stable than C6 RIL population.According to the D values of the two experimental locations,the RILs were divided into three different types:drought-sensitive,moderate-drought-resistant and drought-resistant.RIL 146 and RIL 174 of C5 RIL population were were identified as drought-resistant type at both locatios,while RIL 128 was drought-sensitive;in C6 RIL population,RIL 39 and RIL 231 were identified as drought-resistant type,while RIL 143,RIL 172 and RIL 381 were divided into drought-sensitive group.(3)A total of 955690 SNP(Single Nucleotide Polymorphism)were obtained in both the C5 and C6 RIL populations using GBS technique.After filtering,the linked SNPs were merged into one block marker by similarity/linkage method,a genetic map containing 1275 block markers was constructed for the C5 RIL population and a genetic map containing 945 block markers was constructed for the C6 RIL population.Then QTL mapping was performed using inclusive composite interval mapping.35 drought-related QTL were detected in C5 RIL population,among which 23 were detected in Fenjiang and 12 were detected in Duoying.41 drought-related QTL were detected in C6 RIL population,among which 18 were detected in Fenjiang and 23 were detected in Duoying.Considering the results of the two populations,18,10,7,16,8 and 17 QTL associated with relative chlorophyll content,growth amount,fresh weight,dry weight,plant relative water content and leaves mortality were detected,respectively.(4)Based on the association mapping results for survival rate under drought stress in a panel consisted of 368 maize inbred lines,40 genes containing SNPs significantly associated with the survival rate under drought stress were identified located in 30 drought-tolerance-related QTL detected in this study.Expression analysis was carried out for the 40 significantly associated genes in materials with different drought tolerant sensitivity.There were 18 out of the 40 genes responding significantly to drought stress.At the same time,compared to the drought-tolerance-related QTL during mature period in C5 and C6 RIL populations that identified by Lu,8 consistent QTL for drought tolerance at seedling and mature stages were identified.Seven of them were from the C6 population while the rest one was from the C5 population.The results found this study would provide theoretical and genetic basis for revealing maize drought tolerant genetic architecture and molecular marker assisted selection in maize drought tolerant breeding. |
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