Evaluation Of Drought Tolerance Traits In Tropical Maize Populations And Genome-Wide Association Analysis

Maize(Zea mays L.)is one of the most important food crops in the world and is of great importance to ensure global food security.It is also one of the indispensable raw materials for food,healthcare,light industry and chemical industries.Drought stress is one of the most important abiotic stresses affecting maize production,so breeding quality drought-tolerant maize germplasm is one of the important research areas in current maize breeding.In today’s environment of increasing water scarcity,genetic breeding of maize using genetics,molecular biology,genetic engineering,and biostatistics to select maize varieties with drought tolerance is of great scientific importance to improve the yield of maize.In this paper,tropical germplasm resources with extensive genetic differences were planted in Hainan,China,for two years in 2019,2020,while the corresponding drought tolerance traits were investigated.Drought tolerance index and selection index were calculated from the index data and analyzed for BLUP,heritability and correlation.Then,genome-wide association analysis was performed for eight drought-related traits using SNP markers with uniform coverage of the whole maize genome to locate and screen significant SNP loci associated with drought tolerance phenotypes,and drought tolerance candidate genes regulating drought tolerance traits in maize were screened based on SNP loci.The results of this experiment were as follows.1.The data of the eight drought tolerance traits measured in this experiment showed normal distribution,and the results of the analysis of heritability revealed that the heritability of the eight drought tolerance traits showed different magnitudes of decrease under drought environment,indicating that the drought tolerance traits were controlled by genetic factors.The correlation analysis of the eight drought tolerance traits showed that Dt A was strongly correlated with Dt S,Pla H with Ear H,and GY with SPAD under both drought and normal conditions,while GY was negatively correlated with Dt S and ASI was negatively correlated with GY,and ASI was negatively correlated with GY under drought conditions(Pearson coefficient of-0.27)than under normal conditions(Pearson’s coefficient was-0.18).2.In this experiment,selection index(SI)and stress tolerance index(STI)were calculated and analyzed,and SI and STI were used to describe the drought resistance of the selfed lines.The tropical maize population was mainly divided into marestail maize(population A)and hard-grain maize(population B).The overall traits of the germplasm of population A performed better under drought conditions,and the overall drought resistance of population A was higher than that of population B.The SI and STI values of 13 selfed lines(HD109,HD260,HD266,HD217,HD060,HD102,HD036,HD003,HD111,HD145,HD271,HD149,and HD211)were ranked in the top ten,indicating that these selfed lines have strong drought tolerance.3.In this experiment,the phenotypic data of eight maize drought tolerance traits were analyzed by BULP and also by GWAS with population genotypes,and a total of 143 and 148significant SNPs were detected under both drought stress and normal irrigation environmental conditions.Candidate genes were screened for significant SNP loci appearing only under drought stress environment using the average decay distance of chromosome LD at r~2equal to 0.1,and a total of 80 candidate genes were screened.These candidate genes were mainly functional genes such as heat kinin,iron oxidation reduction protein,zinc finger protein,membrane stabilization protein,NAM protein,phosphotransferase,acyltransferase,etc.The screened genes were all candidates within the association region with drought tolerance traits.4.15 significant loci that appeared only under drought stress were found in multiple traits at the same time,with the phenomenon of multiple effects of one cause.8 candidate genes were screened,GRMZM2G141222、GRMZM2G109914、GRMZM2G137409、GRMZM2G300812、GRMZM2G106680、GRMZM2G007466、GRMZM2G067265、GRMZM2G065928These genes can be used as key targets for future research on drought resistance and other stress mechanisms.