A deep understanding of the genetic control of drought tolerance and iron deficiency tolerance is essential to hasten the process of developing improved varieties with higher tolerance through genomics-assisted breeding. In this context, an improved genetic map with 1205 loci was developed spanning 2598.3 cM with an average 2.2 cM distance between loci in the recombinant inbred line (TAG 24 × ICGV 86031) population using high-density 58K single nucleotide polymorphism (SNP) “Axiom_Arachis” array. Quantitative trait locus (QTL) analysis was performed using extensive phenotyping data generated for 20 drought tolerance- and two iron deficiency tolerance-related traits from eight seasons (2004–2015) at two locations in India, one in Niger, and one in Senegal. The genome-wide QTL discovery analysis identified 19 major main-effect QTLs with 10.0–33.9% phenotypic variation explained (PVE) for drought tolerance- and iron deficiency tolerance- related traits. Major main-effect QTLs were detected for haulm weight (20.1% PVE), SCMR (soil plant analytical development (SPAD) chlorophyll meter reading, 22.4% PVE), and visual chlorosis rate (33.9% PVE). Several important candidate genes encoding glycosyl hydrolases; malate dehydrogenases; microtubule-associated proteins; and transcription factors such as MADS-box, basic helix-loop-helix (bHLH), NAM, ATAF, and CUC (NAC), and myeloblastosis (MYB) were identified underlying these QTL regions. The putative function of these genes indicated their possible involvement in plant growth, development of seed and pod, and photosynthesis under drought or iron deficiency conditions in groundnut. These genomic regions and candidate genes, after validation, may be useful to develop molecular markers for deploying genomics-assisted breeding for enhancing groundnut yield under drought stress and iron-deficient soil conditions.

Iron deficiency chlorosis (IDC) causes a significant reduction in yield of groundnut grown in calcareous and alkaline soils in India. The main aim of the study was to assess genotypic differences for morpho-physiological parameters associated with IDC resistance across different stages and their effect on yield and its related traits. The factorial pot experiment was comprised of two major factors, i) soil-Fe status [normal-Fe, deficit-Fe], and ii) genotypes [five] with differential IDC response, constituting 10 treatments. They were assessed for five morpho-physiological parameters associated with IDC resistance across five crop growth stages and also yield and its related traits. Associations between these traits were also estimated. Under deficit-Fe conditions, IDC resistant genotypes recorded significantly lower visual chlorosis rating (VCR), higher SPAD values, active Fe, chlorophyll content, peroxidase activity, and high yield compared to susceptible ones. Between normal-to deficit-Fe soils, resistant compared to susceptible genotypes showed no change in VCR scores; a lower reduction in SPAD, chlorophyll, active Fe, peroxidase activity, and pod yield. Under deficit-Fe conditions, high yield among resistant genotypes could be attributed to higher seed weight, number of pods and haulm yield, while contrasting reduction in main stem height and number of primaries. The results indicate that for initial large-scale screening of groundnut genotypes for IDC resistance, SPAD values are most ideal while active Fe could be utilized for confirmation of identified lines.

Iron deficiency chlorosis is an important abiotic stress affecting groundnut production worldwide in calcareous and alkaline soils with a pH of 7.5–8.5. To identify genomic regions controlling iron deficiency chlorosis resistance in groundnut, the recombinant inbred line population from the cross TAG 24 × ICGV 86031 was evaluated for associated traits like visual chlorosis rating and SPAD chlorophyll meter reading across three crop growth stages for two consecutive years. Thirty‐two QTLs were identified for visual chlorosis rating (3.9%–31.8% phenotypic variance explained [PVE]) and SPAD chlorophyll meter reading [3.8%–11% PVE] across three stages over 2 years. This is the first report of identification of QTLs for iron deficiency chlorosis resistance‐associated traits in groundnut. Three major QTLs (>10% PVE) were identified at severe stage, while majority of other QTLs were having small effects. Interestingly, two major QTLs for visual chlorosis rating at 60 days (2013) and 90 days (2014) were located at same position on LG AhXIII. The identified QTLs/markers after validation across diverse genetic material could be used in genomics‐assisted breeding.

Iron-deficiency chlorosis (IDC) is an important abiotic constraint affecting the growth and yield of groundnut in calcareous and alkaline soils worldwide. The present study investigated the inheritance of IDC resistance among four straight crosses of groundnut involving four IDC susceptible cultivars as females and a common IDC resistant male parent. The F 1 's of all the four crosses were resistant to IDC indicating the dominant nature of IDC resistance. The F 2 's of all the four crosses showed a good fit to the ratio of 15 (IDC resistant): 1 (IDC susceptible) and their behavior among the F 3 's was as per the expected ratio of 7:4:4:1. The IDC resistance in groundnut is under the control of duplicate dominant genes wherein, the presence of a dominant allele at either of the loci results in IDC resistance, while duplicate recessive results in IDC susceptibility. This information would facilitate development of IDC resistant cultivars of groundnut.

Iron deficiency chlorosis (IDC) is common among groundnut grown in calcareous and alkaline soils in India, China and Pakistan and causes considerable reduction in pod yield. To identify genetically diverse IDC tolerant accessions, the mini-core collection of groundnut representing geographical diversity was evaluated for IDC response over 2 years in iron-deficient calcareous soils. Enormous genetic variability was evident in the mini-core collection for IDC tolerance-related traits such as a visual chlorotic rating (VCR) and SPAD chlorophyll meter reading (SCMR) across five growth stages. Several IDC tolerant sources belonging to different botanical varieties such as hypogaea bunch (ICG # 5051, 6766, 5286, 6667, 4538, 14008, 5663, 9842, 11855), hypogaea runner (ICG 10479), fastigiata (ICG 10890) and vulgaris (ICG # 11651, 118) were identified. Among the six botanical varieties of groundnut, hypogaea bunch types were found most tolerant to IDC and this is the first report in groundnut. The IDC tolerant sources identified were irrespective of their country of origin. The principal component analysis based on VCR, SCMR, pod yield and its related traits revealed five major principal components that explained 80% of the total variation. The biplot generated using PC1 and PC2 revealed a distinct separation of IDC tolerant genotypes from the susceptible ones. The hierarchical clustering using five major principal components revealed seven major clusters that were mainly based on IDC response of the accessions.