Genome-wide Association Analysis For Combining Ability And Heterosis Of Plant Type Traits In Maize

Maize is the most successful crop in the utilization of heterosis.The study of maize heterosis not only provides guidance for the improvement of maize hybrids,but also helps to strengthen the understanding of the genetic mechanism of heterosis.In recent years,the development of bioinformatics provides more abundant technical ways to analyze the genetic mechanisms of heterosis.In this study,three inbred lines Zheng 58,Chang 7-2 and18-599 belonging to different heterosis groups were selected as testers.The hybrids were matched with 360 inbred lines by NCII genetic mating design.The plant type characters of parents and hybrids were measured for calculatingcombining ability and middle parent heterosis.In addition,the heterosis groups and heterosis models of Southwest China were analyzed,which aimed at providing theoretical basis for maize germplasm resources improvement.According to the molecular markers closely associating with plant phenotypic traits,combining ability and mid-parent heterosis,the geneslinked to these markers were screened out to provide genetic resources for molecular breeding...The main results are as follows:1.The phenotypes of parental and F1 plant type traits were significantly different in genotype,environmental principal effect and genotypic × environmental interaction.Broad-sense heritability of each plant type trait was more than 50%,indicating that the inbred lines could be selected in early generation.Among the 11 plant type traits,plant height,ear height and the number of branches of male panicle performedthe strongest heterosis.Additive effect accounted for the main part of the agronomic traits,as revealed by the mean aquare ratios of general to special combining abilities.General combining ability showed no significant correlation with middle parent heterosis and heterozygosity.Special combining ability and middle parent dominance showed significant correlation in plant height,leaf number per ear,internode length of ear,length of male ear and ear position ratio.By comparing SCA effect value with DNA molecular marker cluster.it was found that only some inbred lines were consistent with DNA molecular marker cluster.So the heterosis group should be divided by combining molecular marker and quantitative genetic method.At the same time,the simplified road map of maize heterosis group in Southwest China was proposed based on the K values decreasing from three groups to two groups.2.In the analysis of genotypic heterozygosity,when K= 3,Zheng58(SS)× Tropical,Chang7-2(Tropical)× SS and 18-599(NSS)× SS had higher heterozygosity;When K = 2,Zheng58(Temperate)× Tropical and Chang7-2(Tropical)× Temperate had higher heterozygosity.When K = 3,Zheng58(SS)× Tropical,Chang 7-2(tropical)× Tropical and18-599(NSS)× Tropical were higher than other cross combinations in the plant height,ear height and the number of branches of ear.When K = 2,Zheng 58(temperature)× Tropical and Chang 7-2(Tropical)× Tropical were higher than other cross combinations in the plant height,ear height and the number of branches of ear.The above results indicated that the combinations with high genotype heterozygosity won’t necessarily show high heterosis.3.The phenotypic traits,combining ability and heterosis traits both in parental lines and F1 were used for GWAS by TASSEL.Meanwhile,the corresponding analysis of haplotype and candidate gene were carried out bythese significantlyassociated SNP markers.In the GWAS of F1 plant type trait,the marker PZE-103003537 was detected in different environments and the candidate gene GRMZM2G142179 wasassociated with it.PZE-106054622 was found to be significantly associated with panicle ratio in both parent and F1 plant type traits GWAS and the candidate gene linked to this marker was GRMZM2G142179.Two groups of significantly correlated SNP markers were detected in the number of spike branches.The data showed that,the mean of parental dominance in the number of branches of haplotypes increased graduallywith the increase of haplotype heterozygosity.Two candidate genes,GRMZM2G442658 and GRMZM2G450273,were identified between the two significant locis.These locis we detected are likely to be related to heterosisandthey are worthyfor further study.