Genetic Diversity Of Maize Germplasm Resistant To Southern Rust And Mapping Of Resistance Gene

Maize?Zea mays L.?is an annual gramineous food crop with the largest planting area and the highest total yield in the world as well as in China.Southern corn rust is a worldwide airborne disease caused by Puccinia polysora Underw..The occurrence of this disease is often closely related to climatic conditions,especially the active path of typhoon,with sudden and outbreak,it is difficult to effectively control this disease in production practice.Sowing and utilization of resistant varieties is the safest,economical and effective measure to control southern rust,but most of the major cultivars are susceptible.Therefore,breeding resistant varieties is an important target for maize breeding.Resistance to germplasm is an important material basis for breeding.Therefore,in order to avoid the risk of resistance breakdown due to a single resistance source,excellent germplasm resources with different backgrounds need to be screened for resistances to southern corn rust,and then resistance gene loci,to be discovered and mapped.The main results in this study are as follows:Firstly,maize germplasm resources were screened against southern rust.A total of 903 maize accessions were screened for resistance to Southern Corn Rust in Nanning,Guangxi and Changping,Beijin from 2013 to 2015.And the SSR markers were adopted in genetic diversity analysis of the selected partially resistant materials.In Nanning,Guangxi and Changping,Beijing,both of the results showed that among the 903 germplasm,8 inbred lines were highly resistant to southern corn rust,accounting for 0.88%of the total germplasm.Twenty-nine germplasm,including 27 inbred lines and 2 landraces were resistant to this disease,accounted for 3.2%of total accessions;100 germplasm was moderately resistant,accounted for 3.2%of total accessions;In addition,181 and 585 accessions were susceptible and highly susceptible,accounting for 20.0%and 64.8%of the total materials,respectively.It can be seen that maize germplasm with high resistance to southern corn rust is relatively scarce and hence the highly resistant accessions expressed in both areas are the valuable resources.There exists difference in resistance to southern corn rust among maize germplasm from different geographical areas;and the resistant germplasm was most frequently screened from Inner Mongolia,followed by Shanxi.Secondly,genetic diversity of germplasm resistant to southern rust was analyzed.Fourty-two pairs of polymorphic SSR primers were detected and a total of 141 alleles were amplified in the 50 accessions,including 139 polymorphic bands,with polymorphic site percentage?PPB?of 98.58%.The average number of alleles?Na?was 1.98,the average effective number of alleles?Ne?was 1.59,with the average Nei's gene diversity?H?of 0.34.The average polymorphism information content?PIC?and Shannon's information index?I?were 0.78 and 0.51,respectively.Using UPGMA analysis,the 50 maize accessions were classified into two groups,of which the first group contains five heterosis subgroups with relatively high genetic diversity,which can provide reference information for the selection and utilization of resistance sources for breeding.Thirdly,the QTL loci associated with resistance to southern rust were mapped.The susceptible inbred Huangzaosi was used as the female parent and the resistant cultivar W456 as the male parent to construct an F₂ population derived from a cross between the susceptible inbred Huangzaosi and resistant W456 was used for genetic analysis and for mapping resistance gene.The 1:3 ratio of resistant to susceptible plants indicated that the resistance is controlled by one recessive gene in W456.Using the mapping population containing 240 individuals,a framework of linkage map comprising of 200 SSR markers was constructed to map resistance genes.The map covered 3331 cM of the maize genome with an average marker interval of 16.6 cM.QTLs associated with resistance to southern rust in maize were analyzed using the QTL Ici Mapping V4.1 package for inclusive composite interval mapping.As a result,six QTLs such as qSCR3,qSCR7,qSCR8-1,qSCR8-2,qSCR9 and qSCR10 were detected on chromosomes 3,7,8,9 and 10,respectively.These six QTLs were flanked by markers umc2105 and umc1729,umc1066 and bnlg2271,umc1904 and umc1984,umc1984 and bnlg1651,umc1957 and bnlg1401,and umc2034 and umc1291,respectively.The phenotypic variance explained?PVE?ranged from 2.61%to 24.19%,which could explain62.3%of the total phenotypic variation.The QTL locus on chromosome 10 accounted for 24.19%of the phenotypic variation,which is a major QTL responsible for resistance to southern rust in maize,and further narrowed its positioning range to 2.51 cM,the distance to the flank marks is 2.15cM and 0.36cM,respectively.It can provide a reference for cultivating resistant varieties.Finally,discovery of southern rust resistance gene in maize was performed.In this study,genetic variations related to resistance to southern rust was analyzed by whole genome re-sequencing in Huangzaosi×5364 F ₂ population.A total of 2 candidate regions related to disease resistance traits were obtained,with the total interval of 14.96 Mb,and 1,415 genes were annotated in this region.Among them,395 genes were non-synonymous mutation SNP?single nucleotide polymorphism?loci and 114 were frameshift mutation genes,which were located on chromosomes 4 and 10.Functional enrichment analysis showed that 145 genes accounted for 42.27%of the total number of annotated genes associated with cellular processes,and it was inferred that there might be genetic variation related to disease resistance.The results will be contributed to further understanding genetic mechanism of resistance to southern corn rust.