Identification Of Resistant Varieties To Southern Corn Rust And Mapping Of Resistance QTL

Maize is an important food crop in China,which has the characteristics of high yield,wide adaptability,rich nutritional value and wide use and so on.Puccinia polysora Underw through the air and causes Southern corn rust in maize production areas.Due to climate change,variety replacement,and changes in cultivation systems and other reasons,Southern corn rust has become serious in recent years,posing a great threat to maize production.Promoting planting of disease-resistant varieties is the most economical and effective way to control the disease,and mapping QTLs for resistance to Southern corn rust in maize can provide theoretical guidance for breeding of disease-resistant varieties.Maize varieties with high resistance to Southern corn rust are scarce in production.In this study,85 maize varieties of different types were screened and identified for resistance to Southern corn rust.At the same time,using the S₁₂of RIL population constructed by inbred lines 80007 and 80044 as materials,according to the phenotypic data of three environments,combined with the constructed high-density genetic linkage map,QTL mapping of Southern corn rust resistance was carried out.The main results are as follows:1.Through artificial inoculation,85 different types of maize varieties were identified for their resistance to Southern corn rust.The results showed that there were only 7 highly resistant varieties,26 resistant varieties,20 moderately resistant varieties,18 susceptible varieties and 14 highly susceptible varieties,accounting for 8.2%,30.6%,23.5%,21.2%and16.5%of the identified materials,respectively.In this study,seven varieties with high resistance to Southern corn rust were selected to provide scientific basis for rational seed use,disease control and food security.2.The"80007×80044"RIL population and its parents were identified for their resistance to Southern corn rust.The parent 80007 was resistant to Southern corn rust,and the parent80044 was susceptible to Southern corn rust.The RIL population showed continuous variation,which was consistent with the genetic characteristics of quantitative traits and could be used for QTL mapping.3.The"80007×80044"RIL population and its parents were genotyped using the Maize6K SNP chip of the Infinium platform,and 1150 SNP markers were finally obtained through screening.The genetic linkage map was constructed using QTL Ici Mapping V4.2software.The total length of the map is 2197.2c M,which was evenly distributed on 10 maize chromosomes,and the average distance between markers is 1.9c M.The map constructed in this experiment meets the requirements of QTL mapping.4.Through the QTL mapping analysis of resistance to Southern corn rust in three environments of Huangliu（natural disease）in Hainan in the winter of 2021,Mazhuang（artificial inoculation）in Taian in the summer of 2022,and Huangliu（natural disease）in Hainan in the winter of 2022,it was found that:A total of 2 main QTLs were mapped in Hainan in 2021,named qSCR6-2 and qSCR7-2,which explained 13.25%and 11.22%of the phenotypic variation,respectively.In 2022,only one major QTL resistant to Southern corn rust was mapped on chromosome 6 in Taian,and it was named qSCR6-3,which explained18.94%of the phenotypic variation.Three QTLs resistant to Southern corn rust were mapped in Hainan in 2022,named qSCR6-4,qSCR6-5,and qSCR10,respectively.By analyzing the QTL mapping results of the three environments,it was found that qSCR6-2,qSCR6-3 and qSCR6-4 on chromosome 6 were the same resistance sites,explaining 13.25%,18.94%and8.64%of the phenotypic variation,respectively.The resistance sites were all from the parent80007,located between markers PZE-106041753 and markers PZE-106037747,and the physical location was 92.3Mb-104.8Mb.5.According to the localization interval of qSCR6-2 and the genotype of the gene chip,we screened 18030,18123,18179,18276,and 18332 lines with 5 target intervals as heterozygous segments from the RIL population.The genotype data of the gene chip is the data of the S₆generation of the RIL population,which is different from the generation number of the current population QTL mapping,so it is necessary to identify the genotypes of these 5lines.After identification,the target intervals of these 5 lines were all homozygous,so these families could not be used directly.Through further genotype screening,13 lines were selected and 8 hybrid combinations were selected,and the next fine mapping was carried out by using the hybrid progenies.