Association Mapping for Drought Tolerance in Watermelons (Citrullus lanatus L.)

Drought stress significantly impacts global agricultural productivity, necessitating the identification of resilient genotypes and genetic markers to develop stress-tolerant crops. This study evaluates 48 watermelon (Citrullus lanatus L.) genotypes under controlled drought conditions to assess their morphological, physiological, and molecular responses. Key parameters such as root length, plant height, stem diameter, SPAD index (Soil and Plant Analysis Development index), and MDA levels (Malondialdehyde) were measured. Genotypes W20, W48, W13, and W60 exhibited superior drought tolerance, characterized by enhanced biomass retention, water-use efficiency, and photosynthetic capacity. Correlation analysis revealed significant relationships among traits, such as a strong positive correlation between plant height and stem diameter (r = 0.84) and a negative correlation between MDA and root length (r = −0.99), underscoring the physiological trade-offs under stress. Molecular analyses using inter-primer binding site (iPBS) markers showed a high polymorphism rate (93.2%) and identified 18 markers significantly associated with drought-related traits. Markers iPBS-2239 and iPBS-2400 emerged as highly informative, offering the potential for marker-assisted breeding. This integrative approach highlights the complex mechanisms underlying drought tolerance in watermelons and provides valuable genetic resources and candidate genotypes for developing drought-resilient cultivars. These findings contribute to advancing breeding strategies to address the challenges of climate change and water scarcity in agriculture.