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In vivo haploid induction based on maternal haploid inducers is the first step in deriving completely homozygous maize doubled haploid (DH) lines. Haploid induction rate (HIR) is influenced by both pollen parent inducing haploidy and the maternal source germplasm used in induction crosses. This study was aimed at analyzing the influence of source germplasm on HIR using 671 tropical inbred lines organized in two association mapping panels. These two association mapping panels (AMP1 and AMP2) were crossed to two different Tropically Adapted Inducer Lines (TAILs). For HIR assessment, seeds from induction crosses were planted in the field and ploidy status of each surviving plant was assessed using a gold standard classification based on visual differences between the haploid and diploid plants. The analysis revealed significant variation for HIR and led to identification of several tropical inbred lines that respond very positively to haploid induction. Use of HIR data in a genome wide association study (GWAS) led to identification of twenty-seven and two SNPs that were significantly associated with HIR in AMP1 and AMP2, respectively. Meta-analysis of AMP1 and AMP2 GWAS led to identification of 52 SNPs with significant effect on HIR across both studies. Genome-wide prediction revealed moderate to high prediction accuracy within AMPs using random SNPs. Inclusion of the SNPs detected in GWAS into the prediction model led to improvement in prediction accuracy. Overall, the study revealed that the maternal influence on HIR is controlled by a few moderate and many small effect QTL. Keywords: Maize, Doubled haploid, Haploid induction, Association mapping, Genomic prediction

Key message Genome-wide association study (GWAS) on 923 maize lines and validation in bi-parental populations identified significant genomic regions for kernel-Zinc and-Iron in maize. Abstract Bio-fortification of maize with elevated Zinc (Zn) and Iron (Fe) holds considerable promise for alleviating under-nutrition among the world’s poor. Bio-fortification through molecular breeding could be an economical strategy for developing nutritious maize, and hence in this study, we adopted GWAS to identify markers associated with high kernel-Zn and Fe in maize and subsequently validated marker-trait associations in independent bi-parental populations. For GWAS, we evaluated a diverse maize association mapping panel of 923 inbred lines across three environments and detected trait associations using high-density Single nucleotide polymorphism (SNPs) obtained through genotyping-by-sequencing. Phenotyping trials of the GWAS panel showed high heritability and moderate correlation between kernel-Zn and Fe concentrations. GWAS revealed a total of 46 SNPs (Zn-20 and Fe-26) significantly associated (P ≤ 5.03 × 10−05) with kernel-Zn and Fe concentrations with some of these associated SNPs located within previously reported QTL intervals for these traits. Three double-haploid (DH) populations were developed using lines identified from the panel that were contrasting for these micronutrients. The DH populations were phenotyped at two environments and were used for validating significant SNPs (P ≤ 1 × 10−03) based on single marker QTL analysis. Based on this analysis, 11 (Zn) and 11 (Fe) SNPs were found to have significant effect on the trait variance (P ≤ 0.01, R2 ≥ 0.05) in at least one bi-parental population. These findings are being pursued in the kernel-Zn and Fe breeding program, and could hold great value in functional analysis and possible cloning of high-value genes for these traits in maize. Electronic supplementary material The online version of this article (10.1007/s00122-018-3089-3) contains supplementary material, which is available to authorized users.

Temperature is the one of the most important environmental factor influencing plant growth and development limiting the crop productivity. Groundnut (Arachis hypogaea L.) is a major crop cultivated in tropical and sub-tropical regions where high temperature stress is a serious constraint for its production. In the present study, groundnut genotypes were screened for thermotolerance using temperature induction response (TIR) technique, where the seedlings were exposed to sub lethal temperature from 38°C-54 °C for 5 h followed by lethal temperature at 58 °C for 3 h. From the 100 diverse genotypes screened, 24 genotypes showed tolerance to high temperature with mean percent seedling survival of 92%, 30 genotypes showed moderate tolerance and 46 genotypes were identified as temperature susceptible compared with checks (100% survival). The expression patterns of selected six groundnut genotypes Kadiri 9, Narayani, Dharani, JL 24, TPT-3 and Kadiri 6 at seedling stage were analyzed under heat stress using Quantitative real-time reverse transcriptase PCR (qRT-PCR). qRT-PCR analysis revealed stress responsive nature of the selected genes. Stress responsive genes such as heat shock protein 90 (HSP90), dehydration responsive element binding-2A (DREB2A) and late embryogenesis abundant4-2 (LEA4-2) showed more than 20–50 fold increase in expression level in selected genotypes.

Maize has traditionally been the main staple diet in the Southern Asia and Sub-Saharan Africa and widely grown by millions of resource poor small scale farmers. Approximately, 35.4 million hectares are sown to tropical maize, constituting around 59% of the developing worlds. Tropical maize encounters tremendous challenges besides poor agro-climatic situations with average yields recorded