| Summary: | Within the tomato clade, <i>Solanum chilense</i> is considered one of the most promising sources of genes for tomato (<i>S. lycopersicum</i>) selection to biotic and abiotic stresses. In this study, we compared the effects of drought, high temperature, and their combination in two cultivars of <i>S. lycopersicum</i> and six populations of <i>S. chilense</i>, differing in their local habitat. Plants were grown at 21/19 °C or 28/26 °C under well-watered and water-stressed conditions. Plant growth, physiological responses, and expression of stress-responsive genes were investigated. Our results demonstrated strong variability among accessions. Differences in plant growth parameters were even higher among <i>S. chilense</i> populations than between species. The effects of water stress, high temperature, and their combination also differed according to the accession, suggesting differences in stress resistance between species and populations. Overall, water stress affected plants more negatively than temperature from a morpho-physiological point of view, while the expression of stress-responsive genes was more affected by temperature than by water stress. Accessions clustered in two groups regarding resistance to water stress and high temperature. The sensitive group included the <i>S. lycopersicum</i> cultivars and the <i>S. chilense</i> populations LA2931 and LA1930, and the resistant group included the <i>S. chilense</i> populations LA1958, LA2880, LA2765, and LA4107. Our results suggested that resistance traits were not particularly related to the environmental conditions in the natural habitat of the populations. The expression of stress-responsive genes was more stable in resistant accessions than in sensitive ones in response to water stress and high temperature. Altogether, our results suggest that water stress and high temperature resistance in <i>S. chilense</i> did not depend on single traits but on a combination of morphological, physiological, and genetic traits.
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