Evaluation Of Breeding Potential And Dissection Of Genetic Basis Of Stress Related Traits For Maize-Teosinte Distant Hybridization Populations

Maize(Zea mays L.)is an important food and fodder crop in the world.Its production and quality could affect the food security and quality of life directly.Teosinte,as an ancestor of maize,has abundant genetic diversity and plays a key role in resistance breeding that serves as an excellent alien germplasm resource.However,there were few reports on the evaluation of breeding potential of teosinte to maize yield.As two important abiotic stresses in the whole growth period of maize,drought and low phosphorus stresses could directly reduce the growth and development of maize seedlings and also decrease the yield of maize at the mature stage.In this study,six maize-teosinte distant hybridization populations including unequal number of backcrossed recombinant inbred lines(RILs)were utilized.The breeding potential of teosinte for maize yield was explored through phenotypic identification in several environments and a series of yield trail,and then 31 agronomic traits were mapped by constructing genetic linkage map with molecular marker Bin.Meanwhile,a total of 215BD(B73 × Zea diploperennis)RILs were conducted with drought tolerance identification at both seedling and adult stage,and quantitative trait loci(QTL)was also mapped.Genome wide association study(GWAS)of 13 traits with a total of 356 inbred lines under two phosphorus levels was carried out.Finally,QTL or candidate genes under two abiotic stresses were co-localized.The main results are as follows:1.In this study,four different teosintes were crossed with four maize elite Inbred lines,and six distant hybridization populations were obtained at last.The results of phenotypic identification of 31 agronomic traits in six environments and two years showed that most traits in six populations have abundant phenotypic variations,and many inbreds showed extreme phenotypes with stable inheritance.In addition,in RN(RP125 × Zea nicaraguensis)and ZP(Zheng58 × Zea mays ssp.parviglumis)test-cross hybrids,there were 29 and 47 hybrids showed higher yield than the checks,respectively.Moreover,there were 4 and 2 hybrids with the yield gain of 5% or more,respectively.In the North Carolina mating design II experiment,7 hybrids showed higher grain yield than the check,and inbred lines BD138 and MP048 had higher general combining ability than the checks of inbreds,respectively.Meanwhile,the combining ability analysis indicated that all traits in the study were mainly affected by additive effects.2.In this study,31 agronomic traits of BD population were mapped under five environments in two years.A total of 227 QTL were mapped by Bin-mapping method,and four QTL were detected simultaneously under at least four environments,namely q DTA9＿1,q DTA9＿2,q REP5 and q RNE8.Marker Bin 8.51 on chromosome 8 may include the major QTL(q EH8＿2 and qREP8＿2)that significantly associated with ear height and ratio of ear height and plant height,meanwhile,q EH8＿2 located in the reported QTL of ear height.Fourteen candidate genes associated with six traits were co-identified by single-marker method and GWAS.3.Drought tolerance identification of BD population at seedling and adult stages was conducted,and a total of 206 and 39 inbred lines were screened with higher drought resistance index than the check B73,respectively.Among these inbreds,there were 38 inbred lines showed higher drought resistance index both at seedling and adult stages.At the same time,linkage analysis of drought-related traits was carried out.A total of11 quantitative trait loci(QTL)under well-watered and water-stress conditions were mapped and 5 of which were key QTL associated with drought tolerance in maize seedling stage.For maize adult stage,97 QTL under two water conditions were identified and 5 of which were key QTL associated with drought tolerance.Functional annotations were carried out with genes associated with these important drought-related QTL,among which three candidate genes Zm00001d010775,Zm00001d010776 and Zm00001d000762 identified at adult stage and one candidate gene Zm00001d007629 identified at seedling stage were considered to be responsive to maize drought stress.In addition,single-marker method was used to co-mapping plant height at both seedling and adult stages.As the result showed,one candidate gene was co-identified under normal irrigation condition and another one was co-identified under drought treatment.Moreover,three candidate genes for plant height with the ratio of drought and normal conditions were co-identified.In all,these candidate genes may be involved in plant growth and development and play key roles in abiotic stress resistance during the whole growth period of maize.4.In this study,identification of 356 elite maize inbred lines under normal and low phosphorus conditions was conducted,and six low phosphorus sensitive and seven low phosphorus tolerant inbred lines were screened.GWAS of 13 maize seedling traits under normal and phosphorus deficient conditions was carried out with 541,575 highquality SNPs.A total of 2,245 significant SNPs associated with 2,649 genes were identified.Among these associated genes,16 important candidate genes related to low phosphorus tolerance were selected according to functional annotation information and gene ontology(GO)analysis of candidate genes.In addition,haplotype analysis of candidate gene GRMZM2G009544 revealed that Hap5 had the most favorable alleles among the five haplotypes,and also had larger number of total root tips(TRT),root forks(RF)and greater of total root length(TRL)under two phosphorus levels.These favorable alleles and haplotypes were conducive to molecular marker-assisted selection breeding in the future.5.The results of linkage analysis of drought-tolerance-related traits in BD population at seedling stage and GWAS of low-phosphorus-tolerance-related traits in natural population at seedling stage were comparatively analyzed.Two candidate genes related to total root volume(TRV)under normal condition and 5 candidate genes related to abiotic stress were identified.According to the functional annotation information of these genes,candidate gene Zm00001d014117 and Zm00001d006553 may simultaneously respond to abiotic stresses,such as drought and low phosphorus stresses.In summary,this study demonstrated that teosinte could serve as an alien germplasm resource with a high breeding potential and theoretical genetic research value for maize.Meanwhile,a number of QTL related to maize agronomic traits and stress related traits were identified by linkage analysis and GWAS,which could be useful for molecular marker assisted selection breeding and the dissection of genetic basis for stress related traits in maize.