Inheritance Of Resistance To Fusarium Ear Rot On Chromosome 4 In Maize

Maize plays an important role in national food security,used as food,feed and industrial raw materials.The production of maize is faced with a lot of challenges including abiotic and biological stress.Among them,maize ear rot is one of the most important diseases that brings serious damage to the maize production with 5-10% of incidence and even more than 50%.This is a fiingal disease caused by many pathogens.The most important one is Fusarium verticillioides which not only leads to maize yield and quality reduction,but also has a serious effect on human and animal health because of toxins such as fumonisins.Selection and deployment of disease-resistant varieties is the basic way to control maize ear rot.Identifying loci and allels involed in resistance to maize ear rot and understanding the resistant mechanisms can better serve the breeding practice.In this paper,lingkage analysis combined with association study and QTL_seq was used to dissect the resistance to maize ear rot.Simultaneously,two important QTL on chromosome 4 were mapped furtherly and related genes were analyzed.The main results as follows:1)Based on RIL population of 248 lines,five QTLs for resistance to Fusarium verticillioides ear rot were detected in five environments,whice were located on chromosome 2,3 and 4,respectively,with an 7-19% explaination of phenotypic variation.Three QTLs was detected in combined analysis,which were located on chromosome 3 and explained 7-9% of the phenotypic variation.A QTL named qRfvl was newly detected in different environments and the QTL qRfv2 had the largest effect on resistance to maize ear rot.Through the analysis of the joint more environment found 3 QTL,located on chromosomes 3 and 4,respectively.Among them,located on chromosome 4 qRfvl is a new QTL,in multiple environments were detected,and qRfv2 with the largest effect.2)Eight significant candidate regions related to resistance were found using QTL_seq,located in 1,4,7 chromosomes.Six of eight candidates regions were located on chromosome 4.One of the most significant candidate regions of 2Mb overlaped partly with qRfv1.3)A natural population of 243 maize inbred lines was used to perform genome-wide association analysis.A total of 76 SNPs were detected at P < 10^-4 significance which positioned on ten chromosomes.57 genes were found near these SNPs.The functions of the proteins coded by these genes were divided into several groups such as hydrolytic enzymes,disease resistance and so on.4)Based on two mapping strategies,qRfv2 was narrowed to an interval of about 1.2Mb between markers IDP4548 and indel-4 and can decrease 0.5 and 0.65 disease grade in RIL population and NILs,respectively.Combining QTL_seq with RNA_seq and association analysis,two candidate genes,GRMZM2G404121 and GRMZM2G006219 were found ,which belonged to AGO and VAMP groups,respectively.These two genes were significantly upregulated after inoculating Fusarium verticillioides compaired with water control.5)qRfvl was verified by NILs in two environments and can improved about 6% of the resistance.qRfvl was furtherly mapped to 2Mb interval using QTL_seq.A candidate gene GRMZM2G398755 was found combinating QTL_seq with RNA^seq.This gene was simplely verified by a combination of genome-wide association analysis,qRT-PCR and gene structure analysis.The gene showed a significant upregulation after inoculating Fusarium verticillioides in transcriptome expression analysis and qRT-PCR in BT.By sequencing,the gene sequences were very different between BT-1 and N6.