| Drought stress is one of the most critical abiotic factors constraining the production of crops.Maize is the world’s most widely grown crop,which is particularly sensitive to drought stress at flowering stage,resulting in serious loss of grain yield.Drought stress influence silk extension rate,thereby affecting the anthesis-silking interval(ASI).The extended ASI causes floral asynchrony that can results in bareness which greatly reduces yield.Drought tolerance in maize is a complex and polygenetic trait.The genetic basis and the underlying molecular mechanism of drought tolerance especially at maize flowering stage still remain to be explored.Therefore,the present study was aimed at identifying the genetic basis of maize drought tolerance at flowering stage using Genome-wide association study(GWAS)and linkage mapping.In this study,an association panel comprising of 279 inbred lines and a population of 121 recombinant inbred lines(Recombinant Inbred Line,RILs)were evaluated for ASI,plant height and ear biomass at the silking date under field water stressed(WS)and well-watered(WW)conditions.Results of phenotypic data analysis showed that ASI was extended by 23.09% from 4.33(WW)5.33 days(WS),ear biomass was decreased by 17.44% from 1.42 g(WS)to 1.72 g(WW)and the plant height was reduced by 12.29% from 127.41 cm(WW)111.76 cm(WS)under drought stress within the association panel across the three years respectively.Similarly,in RILs population,drought stress increased the ASI by 33.49% from 4.36(WW)5.82 days(WS),reduced the ear biomass by 19.13%from 2.41 g(WW)to 1.95 g(WS),and decreased the plant height by 14.65% from 106.07 cm(WW)to90.53 cm(WS)respectively across the two years.Genome wide association study(GWAS)was carried out using drought-tolerance index for the three traits applying mixed linear model controlling both population structure and relative kinship.Totally,17 SNPs located in 13 genes,48 SNPs in 18 genes and 6 SNPs in 5 genes under WS,WW and drought tolerance index(WS-WW)respectively were significantly associated(–log p > 5.0)with ASI.49 SNPs in 23 genes,93 SNPs in 43 genes and 17 SNPs in 15 genes under WS,WW and drought tolerance index(WS/WW)respectively were significantly associated(–log p > 5.0)with ear biomass at silking date,while 9 SNPs in 7 genes,9 SNPs in 6 genes and 3 SNPs in 3 genes under WS,WW and WS/WW conditions respectively were significantly associated with plant height.Four genes encoding ARABIDILLO-1(Zm00001d029938),Glycoprotein(Zm00001d029937),Zinc finger family protein(Zm00001d011298),and Tic22-like family protein(Zm00001d039319)were associated with ASI,and one gene encoding 26 S proteasome non-ATPase regulatory subunit-9(Zm00001d020506)was associated with ear biomass,under both well-watered and water stress regimes,which suggest the substantial role of these genes in inflorescence development under both WS and WW conditions.One gene encoding Pyridoxal phosphate dependent transferase(Zm00001d013992)was associated with ear biomass under drought treatment in consecutive two years.Pyridoxal phosphate(PLP)is an active form of pyridoxine which functions as coenzyme in a several reactions like decarboxylation,deamination as well as transamination and mainly involved in biosynthesis of amino acids.A total of 51 QTLs with LOD > 2.5 were identified for all the three traits under two water regimes and drought tolerance index across the two years by linkage mapping.Among them,9 QTLs for ASI with phenotypic variation explained(PVE)in the range of 10.83-29.84%,12 QTLs for ear biomass with PVE 8.47-30.44%,and 11 QTLs for plant height with PVE 9.82-22.24% were identified under WS and drought tolerance index(WS/WW)in two-year environments.The physical distance for these QTLs on individual chromosomes were ranging from 1.23-49.18 Mb,0.34-57.64 Mb,0.54-17.36 Mb for ASI,ear biomass and plant height respectively.Three chromosomal regions,Chr.5: 65.9-88.04 Mb,Chr.2: 23.7-45.8 Mb and Chr.7: 123.5-133.9 Mb harboured QTLs for ASI and ear biomass that were consistently detected and partially overlapped for two years environments.These regions may contain genes involved in maize inflorescence development and contribute to drought tolerance.The candidate genes and main-effect QTLs identified in this study might be promising candidates for drought tolerance at flowerage stage in maize.We provide genetic resources which could be used for drought-tolerance marker development and benefit for future marker assisted drought tolerant maize breeding,although further analyses are needed for functional verification of these genes in the future. |
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