QTL Meta-analysis And Bulked Segregant Sequencing Of Gray Leaf Spot Resistance In Maize

Maize gray leaf spot(GLS) is one of the most serious foliar diseases all over the world, which was caused by the fungal pathogen Cercospora zeae-maydis Tehon & Daniels. Gray leaf spot in maize has become increasingly serious in China since the 1990 s, and it has been an important foliar disease especially in northeast and southwest China maize growing zones. Therefore, it will be of great theoretical significance and practical value to understand the genetic mechanism and breed for GLS resistance in maize. In this research, a preliminary study of resistance to GLS in maize was carried out in the following two aspects: meta-analysis of GLS resistant QTL and de novo bulked segregant sequencing of resistance vs. susceptible plants. The main results are given as follows:1. By integrating a total of 65 available quantitative trait loci(QTL) for GLS in maize based on IBM2 2008 neighbors, 11 consistent QTL were identified using meta-analysis approach. These QTL were found on chromosome bins 1.05, 1.06, 2.03, 2.07, 3.02, 4.05, 5.03, 5.05, 7.02, 8.07, and 9.03, and the corresponding positions on the genetic map were 442.21, 528.27, 228.10, 478.00, 74.65, 311.59, 169.62, 302.35, 205.05, 422.70, 257.93 cM. Consensus QTL regions located on chromosome bins 1.05 and 1.06 with more reports and phenotypic contributions were selected to search for genes on MaizeGDB website, with 324 genes identified. Since most resistance proteins contain conserved motifs, 324 genes were projected onto Oryza sativa and Arabidopsis thaliana genomes on the website of Phytozome. As a result, seven and three genes that located on chromosome bins 1.05 and 1.06 were selected to be as candidate genes for resistance to GLS in maize.2. About 25-30 plants from each of extreme resistant and susceptible plant groups were selected from one F2 population that developed from Suwan1 and HM04 and one BC1F1 population that developed from Suwan1 and HM01, and each population included about 500 individuals. A total of five bulks were developed to perform genotyping by bulked segregant sequencing, with two resistant(bulks 1 and 2) and one susceptible(bulk 3) bulks from F2, and one resistant(bulk 4) and one susceptible(bulk 5) bulks from BC1F1. Bulked segregant sequencing analysis indicated that 26 and 22 putative loci were identified by comparison analysis of bulk 1 vs. bulk 3, bulk 2 vs. bulk 3 in F2, while 32 putative loci were identified by comparison analysis of bulk 4 vs. bulk 5 in BC1F1. Among these loci, four(on chromosomes 4, 5, 7, and 10) were identified in both the F2 and BC1F1 populations, of which the first three were consistent with the loci identified by meta-analysis. Moreover, for the three candidate regions that were resistant to GLS with significant difference in bulked segregant sequencing analysis, one candidate gene for GLS resistance in each region was selected using bioinformatics methods.In summary, three consistent loci for GLS resistance were identified in this study using QTL meta-analysis and bulked segregant sequencing analysis, which were located on chromosomes 4, 5 and 7. These candidate resistant regions can be targeted for further genetics and breeding of GLS in maize.