Co-60 gamma irradiation induces variation in F₃ watermelon resistance to Macrophomina phaseolina

Gamma radiation has been employed to induce mutations in seeds and to develop disease-tolerant cultivars. This study aimed to assess resistance to Macrophomina phaseolina in F₃ watermelon (Citrullus lanatus) genotypes derived from seeds of the cultivar Sugar Baby irradiated with 200 Gy of Co-60 gamma rays. The experiment was conducted in a greenhouse using a completely randomised design, with 14 treatments, and five replicates. The assay was repeated. The materials evaluated included the melon (Cucumis melo) accession Ag-15591Ghana (G1), non-irradiated Sugar Baby watermelon (G2), and five irradiated watermelon genotypes (G3–G7), obtained through controlled manual pollinations from seeds previously exposed to 200 Gy of gamma radiation. Plants were inoculated with M. phaseolina isolate A11P17, and disease severity was assessed 30 days post-inoculation using a 0–5 rating scale. Genotypes G1 and G2 were susceptible, whereas the irradiated genotypes, particularly G4, exhibited higher frequencies of resistant individuals. The observed genetic variability suggests that gamma irradiation is a promising strategy for improving resistance to M. phaseolina in watermelon, with the potential to reduce disease impact and support yield stability.