Phenotypic variability in the M1 population of Citrullus lanatus (Thunb.) Matsum. & Nakai ‘Sugar Baby’ irradiated with Cobalt-60 gamma rays

Citrullus lanatus (mini-watermelon type) ‘Sugar Baby’ seeds were irradiated with Cobalt-60 gamma rays at doses of 0 (control), 100, 200, 300, and 400 Gy to enhance genetic variability. Germination, anomalies, development, flowering, and fruiting were assessed through 29 quantitative and qualitative traits and 79 molecular markers (random amplified polymorphic DNA (RAPD), intersimple sequence repeat (ISSR), and simple sequence repeat (SSR)). Gamma radiation significantly influenced germination (p < 0.001), with low doses showing neutral or positive effects and higher doses reducing germination. The 50% lethal dose (LD50) was determined as 325.81 Gy. Of 25 evaluated traits, most showed highly significant differences (p < 0.001), with developmental improvements at 100 and 200 Gy and deleterious effects at 300 and 400 Gy. Phenotypic diversity increased with the dose, forming distinct clusters: three at 400 Gy, five at 300 Gy, and fewer at lower doses. Molecular analyses revealed changes induced by two RAPD markers, five ISSR markers, and one SSR marker. Seventeen morphotypes that differed from the control were identified. These results confirm the efficiency of gamma radiation in inducing significant phenotypic and genetic variability, enabling LD50 determination and the detection of previously unreported molecular alterations in mini watermelon.