Morphological and biochemical responses to water stress in Solanum pimpinellifolium and S. lycopersicum var. cerasiforme accessions

Abstract

Drought is a critical abiotic stress that negatively affects the growth and productivity of tomato ( Solanum lycopersicum L.). In this study, we assessed the morphological and biochemical responses of plants from eight accessions of tomato relatives, four of Solanum pimpinellifolium (SP) and four of S. lycopersicum var. cerasiforme (SLC), under control (100% field capacity, FC) and water stress (40% FC) conditions. Growth parameters, including stem, leaf, and root morphology, biomass, water use efficiency (WUE), photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), and osmolytes (proline and total soluble sugars) were assessed. Thedifferences between accessions, treatments, and their interactions were assessed. In drought conditions, the two accessions, ECU689 (SP) and ECU1009 (SLC), were identified as the most drought-tolerant ones. The two genotypes hardly showed a decrease in root water content, root fresh weight, and aerial biomass, as well as small alterations of leaf morphology. All these features point to their better performance of growth and physiological function under stress. Although proline levels increased under water stress in all accessions, the rise was markedly lower in ECU689 and ECU1009, suggesting that these accessions may utilize alternative adaptive mechanisms, such as root resilience and osmotic regulation. PT210 (SLC) demonstrated strong osmotic adjustment, increasing total soluble sugars by 183.2% (86.15 mg eq. glucose g −1 DW under stress). Photosynthetic pigments remained stable across treatments, indicating that the water stress applied was moderate. Principal component analysis (PCA) revealed a clear separation between the control and water stress groups; however, no clear separation was observed between SP and SLC accessions. Among the traits contributing to this differentiation, proline displayed significant positive correlations with photosynthetic pigments under water stress conditions, but not under control conditions. Overall, these findings highlight ECU689 and ECU1009 as promising donor candidates for breeding drought-tolerant tomato varieties, due to their ability to maintain stable root traits and biochemical balance under water stress. In contrast, among the other accessions, ECU1385 (SP) and PI487625 (SLC) were found to be more sensitive to stress. Incorporating these tolerant accessions into tomato breeding programs may facilitate the development of resilient tomato cultivars and rootstocks for drought-prone environments.

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