Influence of Seedling Pretreatment and Explant Type on Watermelon Shoot Organogenesis

Abstract

Several methods have been published on shoot regeneration from watermelon cotyledon explants. The major differences in regeneration protocols include the light environment in which seeds are germinated and the cotyledon region used. The purpose of these experiments was to compare the two main protocols for plant regeneration and develop one general procedure. To fulfill this objective, seeds were germinated in vitro in darkness or 16-hr light photoperiod for 7 days. Cotyledon explants from four watermelon cultivars (`Crimson Sweet', `Minilee', `Sweet Gem', and `Yellow Doll') were prepared from both dark- and light-grown seedlings. Apical and basal halves were obtained by making a cut across the cotyledon width. Apical and basal quarters were made, for comparison, by cutting apical and basal halves longitudinally. All explants were incubated on shoot regeneration medium for 6 weeks followed by a 3-week cycle on shoot elonga-tion medium. The percentage of cotyledons with shoots was 1.7-fold greater for cotyledons derived from seedings incubated in darkness than those germinated in light. Shoot formation was about 10-fold greater for explants from cotyledon basal halves and quarters than apical halves and quarters. According to these results, the best watermelon regeneration protocol should consists of basal explants from in vitro-germinated seedlings incubated in the dark for 7 days.