Adventitious shoots induction and plant regeneration from cotyledons of watermelon (<i>Citrullus lanatus</i> L.)

Abstract

A highly efficient regeneration system is a prerequisite step for successful genetic transformation of
watermelon cultivars (Citrullus lanatus L.). The objective of this study was to establish efficient in vitro plant regeneration for three watermelon cultivars. To achieve optimal conditions for adventitious shoot induction, the 5-day-old explants (cotyledon base portion, apical portion and hypocotyl) of three cultivars were placed on MB5 media supplemented with different concentrations and combinations of growth regulators (1.0 to 10.0 mg L^-1 6-benzyladenine (BA) and 0 to 1.0 mg L^-1 indole acetic acid (IAA)); the explants from seedling of different development stages (0 to 10 d) were cultured on MB5 medium containing 2.0 mg L^-1 BA and 0.2 mg L^-1 IAA for investigating the effect of age on adventitious shoots initiation; besides, 5-day-old seedlings were grown on optimal regeneration medium supplemented with different concentrations of kanamycin for screening the lowest lethal concentration for adventitious shoots. The results show that the basal region of cotyledon showed higher frequency of shoot formation (79.17-83.33%) than the apical region (5.23-8.25%); high  percentage of shoots regeneration was induced from 5-day-old cotyledons base portion cultured on MB5 containing 1 or 2 mg L-1 BA; the 100 mg L^-1 kanamycin proved to be the optimal concentration for screening the transformants. Our results provide an efficient stable regeneration system for genetic transformation of watermelon.

Key words: Watermelon (Citrullus lanatus), cotyledon, growth regulator, kanamycin, regeneration.