Physiological, biochemical and morphological responses of diverse tomato genotypes to early drought stress

Drought stress is a major environmental constraint that significantly affects tomato (Solanum lycopersicum L.) productivity, particularly during early stages of plant development.This study evaluated the physiological, biochemical, and morphological responses of 19 tomato genotypes under early drought stress to identify drought-tolerant cultivars.Seedlings were subjected to drought stress by withholding irrigation for 14 d at 35 d after sowing.Across genotypes, drought caused significant reductions in chlorophyll a by 28%-46%, chlorophyll b by 25%-41%, relative water content (RWC) by 22%-39%, shoot biomass by 30%-55%, and root biomass by 27%-49% compared to non-stressed control plants.Conversely, reducing sugars and phenolic content increased by up to 32% and 47%, respectively, reflecting osmotic adjustment and antioxidant activation.Significant genotypic variation was observed; tolerant cultivars such as BARI-F1-5, BARI-15, BARI-11, and Pathorkuch maintained higher RWC (> 60%), chlorophyll levels more effectively (≥ 70% of control), and stronger root-shoot development (root length up to 24 cm, shoot dry weight up to 1.5 g).In contrast, sensitive genotypes including 'Roma-VF', 'BARI-2', and 'BARI-21' showed significant reductions with chlorophyll content declining below 50% of non-stressed control and RWC reducing to 45%.Multivariate analyses (hierarchical clustering, heatmap, principal component analysis) grouped the genotypes into tolerant, intermediate, and highly sensitive classes.The results indicate that integrating physiological (chlorophyll, RWC), biochemical (sugars, phenols), and morphological (root-shoot growth) parameters provides an effective strategy for screening drought-tolerant tomato germplasm.The identified tolerant genotypes represent valuable genetic resources for breeding programs aimed to enhance tomato resilience in water-limited environments.