The aim of the present study was to investigate the physiological responses of six tomato (Lycopersicon esculentum Mill.) cultivars to water stress. To this end, plants were exposed to slow dehydration at the third unfolded leaf stage for 23 days. The relative water content (RWC), leaf area and leaf L-proline were determined at 10, 17 and 23 days after treatment application. Our results showed that during slow dehydration, the leaf RWC declined in all studied genotypes, whereas L–proline accumulated. A statistically significant effect of the sampling date (water stress duration) on RWC values was also observed. In addition, the differences in proline content were significantly influenced by tomato genotype, sampling date and the level of substrate saturation. Putting all these together, the results of this study indicate that the adaptive potential of the studied genotypes was expressed in a different relationship between the relative water content and growth of the leaf area. However, three of the tomato genotypes exhibited reduced growth in leaf area in response to the decreased RWC, whereas other tomato genotypes retained a balanced RWC accompanied by further growth of the leaf area.
Key words: Tomato, genotypes, growth, water stress, L-proline, relative water content.
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