Abstract
BackgroundHeat tolerance is becoming increasingly important where maize is grown under spring season in India which coincide with grain filling stage of crop resulting in tassel blast, reduced pollen viability, pollination failure and barren ears that causes devastating yield losses. So, there is need to identify the genomic regions associated with heat tolerance component traits which could be further employed in maize breeding program.ResultsAn association mapping panel, consisting of 662 doubled haploid (DH) lines, was evaluated for yield contributing traits under normal and natural heat stress conditions. Genome wide association studies (GWAS) carried out using 187,000 SNPs and 130 SNPs significantly associated for grain yield (GY), days to 50% anthesis (AD), days to 50% silking (SD), anthesis-silking interval (ASI), plant height (PH), ear height (EH) and ear position (EPO) were identified under normal conditions. A total of 46 SNPs strongly associated with GY, ASI, EH and EPO were detected under heat stress conditions. Fifteen of the SNPs was found to have common association with more than one trait such as two SNPs viz. S10_1,905,273 and S10_1,905,274 showed colocalization with GY, PH and EH whereas S10_7,132,845 SNP associated with GY, AD and SD under normal conditions. No such colocalization of SNP markers with multiple traits was observed under heat stress conditions. Haplotypes trend regression analysis revealed 122 and 85 haplotype blocks, out of which, 20 and 6 haplotype blocks were associated with more than one trait under normal and heat stress conditions, respectively. Based on SNP association and haplotype mapping, nine and seven candidate genes were identified respectively, which belongs to different gene models having different biological functions in stress biology.ConclusionsThe present study identified significant SNPs and haplotype blocks associated with yield contributing traits that help in selection of donor lines with favorable alleles for multiple traits. These results provided insights of genetics of heat stress tolerance. The genomic regions detected in the present study need further validation before being applied in the breeding pipelines.
Highlights
Heat tolerance is becoming increasingly important where maize is grown under spring season in India which coincide with grain filling stage of crop resulting in tassel blast, reduced pollen viability, pollination failure and barren ears that causes devastating yield losses
The present study aims to (i) explore the genetic variation for heat stress responsive traits in the doubled haploid (DH) association mapping panel under normal and heat stress conditions across the environments, (ii) identify genomic regions associated with the heat tolerance traits through Genome wide association studies (GWAS) and (iii) identify candidate genes associated with heat stress tolerance
We identified 130 Single nucleotide polymorphisms (SNPs) associated with different traits distributed over all the 10 maize chromosomes but most of them localized on chromosomes 3, 8 and 10 under normal conditions
Summary
Heat tolerance is becoming increasingly important where maize is grown under spring season in India which coincide with grain filling stage of crop resulting in tassel blast, reduced pollen viability, pollination failure and barren ears that causes devastating yield losses. Heat stress (HS) is the more demanding problem which hampers maize production and there is an expectation that heat stress will further reduce the crop yields. It has been forecast that upcoming catastrophe of heat stress will affect the tropical and subtropical regions of the world more based on global climate model analysis [1]. It has been described that central and eastern Asia, central North America and northern part of Indian subcontinents will be more liable regions to suffer from heat stress for growing maize and other crops [2]. It has been reported that global maize yield potential decreases to 45% by 2080s as compared to 1980s at extreme heat stress during anthesis [3]
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