Physiological and genetic deciphering of water, salinity and relative humidity stress in chickpea (Cicer arietinum L.)RPushpavalliauthorChickpea (Cicer arietinum L.), an important cool-season, food legume crop, is known to be sensitive to several abiotic stresses: drought, salinity and heat. The yield losses caused by these stresses are accounted to 6.4 million tonnes (t)/ year on global production. To improve any existing cultivar and harness the genetic regions involved in the tolerance it is important to understand the genetic and physiological mechanisms that underlie any tolerance. The objectives of this study were to (i) understanding the effect of either water deficit or salt stress on the reproductive biology of genotypes know to contrast for either salt or drought stress and (ii) construction of genetic map and identification of QTLs and candidate genes for salinity tolerance in 188 RILs derived from the ICCV 2 × JG 11 cross. In the water deficit study conducted in two consecutive years, ten genotypes with contrasting yields under terminal drought stress in the field were exposed to a gradual, but similar, water stress in the glasshouse. Nine parameters related to yield were recorded in wellwatered plants (WW) and in water-stressed plants (WS) when the level of deficit was mild (phase I), and when the stress was severe (phase II). The WS treatment reduced seed yield, seed and pod number, but not flower + pod + seed abortion percentage or 100-seed weight. The controlled drought imposition in glass house conditions revealed genotypic differences inthe sensitivity of the reproductive process to drought. The seed yield differences in chickpea were largely related to the capacity to produce a large number of flowers and to set seeds, especially when the degree of water deficit was mild. In the salinity experiments, fourteen genotypes of chickpea (Cicer arietinum L.) were used to study yield parameters, and eight genotypes were selected for ion analysis after being grown in soil treated with 0 mM and 80 mM NaCl, to assess any possible relationship between salt ion accumulation in different plant tissues and yield reduction. Salinity delayed flowering and the delay was greater in sensitive than tolerant genotypes under salt stress. Filled pod and seed numbers, but not seed size, were associated with seed yield in saline conditions, suggesting that salinity impaired reproductive success more in sensitive than tolerant lines. The delay in flowering was associated with higher concentrations of Na+ in the laminae of fully expanded young leaves (R2=0.61) and old green leaves (R2=0.51). Na+ accumulation in leaves was associated with delayed flowering that in turn could have played a role of the lower reproductive success in the sensitive lines. In QTL mapping for salinity tolerance, yield and components were assessed in 188 recombinant inbred lines (RILs) derived from cross ICCV 2 × JG 11, in soil treated with either 0 mM NaCl (control) or 80 mM NaCl (salinity) over two consecutive years. Salinity significantly (P<0.05) affected almost all traits across years. The mean yield reduction under salinity compared to control was around 40% across years. A genetic map was constructed using 56 (SSR, SNP) polymorphic markers. The QTL analysis revealed two key genomic regions on CaLG05 (28.6 cM) and on CaLG07 (19.4 cM) that harboured QTLs for salinity tolerance associated traits. Two major QTLs for higher yield in the salinity treatment (explaining 12 and 17% of the phenotyping variation) wereidentified within the two key genomic regions. Comparison with already published chickpea genetic maps showed that these regions conferred salinity tolerance across two other populations and the markers can be deployed for enhancing salinity tolerance in chickpea. Based on gene ontology annotation 48 putative candidate genes responsive to salinity stress were found. Most of them were believed to be involved in achieving osmoregulation under stress conditions. In the relative humidity stress study, five genotypes that contrasting for yield under heat stress were studied. The plants were grown in three different vapor pressure deficit conditions (2.5, 3.0, 3.4 kPa) where the temperature was maintained constant (30°C) and the RH varied as 40, 30, 20% respectively. Genotypic variation found for almost all traits across treatments. The traits seed number and seed weight differentiated tolerant and sensitive group significantly at VPD conditions 2.5 and 3.0 but not in 3.4 kPa. Seed size was unaffected under 2.5 and 3.0 kPa VPD regimes but did get reduced upto 45% under 3.4 kPa treatment compared to 2.5 kPa treatment. The lowest RH treatment, even under fully well-watered condition, as any other abiotic stress reduced yield. Thus, it is important to consider the effect of low RH and the mechanisms behindits tolerance and sensitivity in future heat tolerance studies. The pollen viability or pollen in vivo germination was unaffected in this study. All the four studies have revealed that certain parameters can be used for achieving water deficit, salinity and relative humidity stress tolerance in future chickpea improvement programs.Chickpea2015Bharathidasan University,Tiruchirappalli, Tamil Nadu;Department of Plant Science Center of Excellence in Life SciencesThesis