Identification Of QTLs And Investigation Of Mechanism For Shell Infection Resistance To Aspergillus Flavus In Peanut

Peanut or groundnut(Arachis hypogea L.)is an important oilseed and cash crop extensively cultivated in more than 100 countries in the world,with China being the largest producer and consumer.Further increasing peanut supply,improving peanut quality and ensuring food safety is highly crucial for the economic and social development both in China and many other countries.However,aflatoxin contamination caused by Aspergillus fungi seriously affects the food safety and international trade of peanuts,which is a key factor restricting the sustainable development of peanut industry.Breeding and planting peanut varieties with desirable resistance is the most cost-effective approach to control aflatoxin contamination.Up to date,studies on resistance to aflatoxin contamination have mainly focused on seed infection resistance and aflatoxin production resistance,while less research effort has been made for pod shell infection resistance.There are several factors limiting the pod shell resistance improvement in peanut,including lack of resistant germplasm lines,lack of molecular markers for quick selection and poor understanding of mechanism of shell resistance.In this study,the shell infection resistance in peanut mini-core collection and selected germplasm lines was characterized for screening special resistant genotypes.QTLs related to shell resistance were identified by genome-wide association study and linkage analysis.The resistance mechanism of shell resistance was also preliminarily investigated through analysis of shell strength,carbohydrate content and metabolomic characteristics.The main results are as follows.1.The shell infection resistance in a peanut germplasm panel,consisting of 145 accessions including the Chinese peanut mini-mini core collection,selected accessions from the United States and ICRISAT peanut mini-core collections,and some representative cultivars from China,was repeatedly characterized by artificial inoculation on health mature pods.Differentiation of shell resistance among the cultivated peanut was investigated.The resistant accessions were mainly distributed in intermediate and var.vulgaris belonging to ssp.fastigiata,while the spp.hypogaea is more susceptible to A.flavus infcetion in general.Six accessions were identified as resistant to shell infection.The shell infection resistance was found not correlated with the seed infection resistance and the aflatoxin production resistance in kernel,but the seed infection resistance was found highly positively related with the aflatoxin production resistance.The genotypic data of the Chinese peanut mini-mini core generated by RAD-Seq were used for a genome-wide association study,from which,a total of 6 SNPs/In Dels associated with shell infection resistance were detected and explained 24.80%-38.64% of phenotypic variation(PVE).2.A RIL population consisting of 267 lines,constructed by using XH13 as resistant parent,was phenotyped by artificial inoculation with A.flavus suspension from which the shell infection index(SLII)and shell penetration index(SLPI)were investigated for four environments.Correlation analysis showed that there was a significant positive correlation between SLII and SLPI.QTL mapping was performed for shell infection resistance by using genetic linkage maps of the RILs based on SNP markers.Sixteen QTLs related to SLII were identified,which explained 3.12%-14.75% of phenotypic variation.Among the 16 SLII QTLs,qSLIIA08.2 was detected repeatedly in 3environments.Six QTLs related to SLPI were identified,which explained 4.57%-19.38%of phenotypic variation.Among the 6 SLPI QTLs,qSLPIB07 was detected repeatedly in 3environments.The SLPI of those accessions with “aa” genotypes of either Chr17b047 or Chr17b048 were significantly lower than that of “AA” genotypes.Seven stable resistant lines with SLII and SLPI were obtained,respectively.Among them,QT0167 was resistant both to fungus infection and penetration,which would be useful in further research and breeding.3.The shell strength and sugar content of the peanut RIL population were characterized.The shell strength was found being positively correlated with SLII and SLPI.Both the SLII and SLPI of the accessions with high shell strength were significantly higher than those with low shell strength.The sucrose content in shell was positively correlated with SLII,and the SLII of the accessions with high sucrose content was significantly higher than that of the accessions with low sucrose content.Untargeted metabolomics analysis was performed on shells of the XH13(resistant)and ZH6(susceptible).Three metabolic pathways were identified as related to shell infection resistance based on the metabolomics analysis combined with the analysis of the candidate genes in confidence interval of qSLIIA08.2 and qSLPIB07.