ESTABLISHMENT OF COTYLEDON EXPLANTS REGENERATION SYSTEM IN WILD WATERMELON

Wild watermelon is ideal rootstock for cultivated watermelon grafting because of its graft compatibility, tolerance to environmental stresses, and less effect on the fruit quality of the scion. However, it is hard to acquire the excellent wild watermelon genotype with multiple resistances through traditional breeding programs. Genetic transformation is an efficient approach for genetic improvement. In the study, we analyzed the effect of plant growth regulators on the cotyledon regeneration efficiency with the aim of establishing genetic transformation system for wild watermelon. Wild watermelon (Citrullus lanatus var. citroides) seeds were germinated under aseptic conditions. Cotyledons were cut from five day seedlings and cultured on MS medium supplemented with different plant growth regulators. The results showed that explants cultured in MS + BA (1.0 mg/L) achieved the highest regeneration rate, and 6.3 shoots were regenerated from each explant on an average. Adventitious shoots were able to elongate on MS medium with KT concentrations ranging from 0.1 to 0.3 mg/L. On an average 62% adventitious shoots were successfully rooted on MS medium supplemented with 0.05 mg/L NAA. Rooted seedlings were successfully acclimatized and gradually hardened-off to green-house conditions and subsequently cultivated in soil with a mean survival rate of 80%. The cotyledon regeneration system for wild watermelon was successfully established in the study, which is needed for genetic transformation of wild watermelon in the future.