The efficient physiological strategy of a novel tomato genotype to adapt to chronic combined water and heat stress

Climate change is increasing the frequency of high temperature shocks and water shortage, pointing to the need for developing novel tolerant varieties and to understand the mechanisms engaged to withstand combined abiotic stresses. Two tomato genotypes, a heat-tolerant S. lycopersicum accession (LA3120) and a novel genotype (E42), previously selected as a stable yielding genotype under high temperatures, were exposed to single and combined water and heat stress. Plant functional traits, pollen viability and physiological (leaf gas exchanges and chlorophyll a fluorescence emission measurements), and biochemical (antioxidants contents and antioxidant enzymes activity) measurements were carried out. A Reduced Representation Sequencing (RRS) approach allowed to explore the genetic variability of both genotypes to identify candidate genes that could regulate stress responses. Both abiotic stresses had a severe impact on plant growth parameters and on the reproductive phase of development. Growth parameters and leaf gas exchange measurements revealed that the two genotypes used different physiological strategies to overcome individual and combined stresses, with E42 having a more efficient capability to utilise the limiting water resources. Activation of antioxidant defence mechanisms seemed to be critical for both genotypes to counteract combined abiotic stresses. Candidate genes were identified that could explain the different physiological response to stress observed in E42 compared with LA3120. Results here obtained have shown how new tomato genetic resources can be a valuable source of traits for adaptation to combined abiotic stresses and should be used in breeding programs to improve stress tolerance in commercial varieties.