Inheritance Of Seed Resistance To Fusarium Verticillioides In Maize

Maize?Zea mays L.?is one of the most important cereals in the world for its high yield potential and great demand as food,feed and industrial purpose.Maize is suffered in a variety of biotic and abiotic stress during their lifetime,which seriously affects its final yield and quality.As one of the pathogenic fungi,Fusarium verticillioide?F.verticillioide?can be transmitted by seed and cause systemic infection of maize.The mycotoxin produced by F.verticillioides on the kernel has harmful effect on animal and human health.Using genome-wide association study?GWAS?and linkage mapping for the genetic dissection of seed resistance to F.verticillioides is helpful to understanding the resistant mechannism and exploring functional genes of disease resistance.Materials used in the study contained 217 diverse maize inbred lines and a RTL population?S10?derived from BT-1?resistant?and N6?susceptible?.Based on the identification system of seed resistance,a variety of resistant resourses were sreened and the resistant loci were identified and verified combining GWAS and linkage analysis.Then,Gene expression analysis and structure analysis of the candidate genes were carried on.The main results of this study are listed as follows:1)We established the identification system of seed resistance to F.verticillioide.Results showed that the optimal concentration of bacteria was 1×105 and the the best time for phenotypic investigation was one week later after inoculation.The grades of diseases were divided into 0-7 considering the incidence and the number of diseased seeds of ten seeds in one petri dish.Eleven materials were identified highly resistant to F.verticillioide from 219 maize inbred lines,and those inbred lines will provide important germplasm resources for genetic improvement in resistance breeding.2)Linkage mapping were developed in the RIL population using 207 SSR makers and QTL anlaysis were tested in three environments.Eight QTLs were detected using ICIM model in the combined analysis of three environments,explaining 4.07-12.06% of the phenotypic variation.Five QTLs of them were consistent with previous reported QTLs of fusarium ear rot and three QTLs were special for seed resistance.3)With the phenotypic variation of different grades of diseases and 224,152 SNP detected in 217 diverse maize lines,we conducted the GWAS using the mixed linear model based on the structure analysis and principal component analysis.Totally 57 SNP identifiedassociatd with resistance to F.verticillioide at the significant level of P <4.46×10-4.4)Three loci?chr1.S₆433914,chr3.S₁87896997 and chr5.S₅6372680?detected from GWAS were consistent with the results identified in QTL mapping,and these three loci had more obvious effect on the resistance in the RIL population than other associated loci from GWAS.Meanwhile,the analysis of different combinations of the 3 loci showed different resistant level followed by: [+/+/+]>[+/-/+]>[+/+/-]>[-/+/+]>[-/-/+]>[+/-/-]>[-/+/-]>[-/-/-].Results indicated that chr1.S₆433914 and chr5.S₅6372680 can perform the resistant function independently,while the resistance of chr3.S₁87896997 and chr1.S₆433914 of their corresponding genes may in the same gene networks with chr3.S₁87896997 on the downstream.Also,the NIL contained chr1.S₆433914 can significantly promote the seed resistance to F.verticillioides.5)Forty-three candidate genes derived from the GWAS were found to be involved in responding to plant disease,stress and other functions.Quantitative real-time PCR results showed that three candidate genes identified both by GWAS and QTL mapping were involved in responding to the infection of F.verticillioides.Comparing the resequencing of two parents for BT-1and N6 in the regions of the three candidate genes revealed that the deduced proteins encoded by the gene of chr1.S₆433914 and chr5.S₅6372680 were different in two parents,while no structure difference was identified for chr3.S₁87896997 in two parents.The candidate genes will be useful in maize breeding for improving seed resistance to F.verticillioides.