Effects of gamma ray sources and irradiation doses on the haploidization frequency of citron watermelon (Citrullus lanatus var. citroides)

Drought is widely regarded as the most significant abiotic stressor affecting modern agricultural production. Sweet watermelon (Citrullus lanatus var. lanatus), one of the world’s most cultivated vegetable species, lacks drought resistance and must be grown in dry and semi-arid regions by grafting on tolerant rootstocks. Citron watermelon (Citrullus lanatus var. citroides) is well known for its high drought tolerance and has excellent potential as a watermelon rootstock. There is a high demand for novel citron watermelon cultivars with rootstock potential. Doubled haploid (DH) technology enables the breeding of genetically uniform and fully homozygous plants in a single generation. However, no research has been conducted on the haploidization of citron watermelon using the irradiated pollen technique. The current study aimed to determine the efficiency of gamma-ray sources (Cobalt: Co60 and Cesium: Cs137), irradiation doses (200, 250, and 300 Gy of Co60; 100, 150, 200, and 250 Gy of Cs137), and genotypes (11 citron watermelon lines) on the production of pure citron lines via the irradiated pollen technique (parthenogenesis). The embryos were grown on MS medium supplemented with 0.4 mg/L indole-3-butyric acid. Stomatal observations and flow cytometry were used to conduct ploidy studies on 3–4 weeks old parthenogenic plantlets. The Co60 treatments yielded eight haploid and two mixoploid plants, while the Cs137 treatments yielded 14 haploid and one mixoploid. These findings demonstrated that gamma rays from both radiation sources were effective in parthenogenic embryo induction, and Cs137 was discovered to be a reliable alternative to conventional Co60.