Dark pretreatment improves adventitious shoot organogenesis from cotyledons of diploid watermelon

The influence of light incubation during embryo germination on shoot organo genesis from cotyledons of four diploid watermelon [Citrullus lanatus (Thum b.) Matsum. & Nakai] cultivars was examined. Germinating embryos in darknes s significantly improved the number of explants that produced harvestable s hoots during the 6 week incubation period on shoot regeneration medium unde r a 16-h photoperiod. The percentage of explants with shoots more than doub led for 'Crimson Sweet' and was about 1.5-fold greater for 'Sweet Gem' and 'Yellow Doll' when embryos were germinated in darkness. The percentage of e xplants with shoots was not significantly improved for 'Minilee' by pretrea ting seedlings in darkness. This study demonstrates that optimal shoot rege neration can be obtained by germinating embryos in darkness before preparin g cotyledon explants.