Dark pretreatment improves adventitious shoot organogenesis from cotyledons of diploid watermelon

The influence of light incubation during embryo germination on shoot organogenesis from cotyledons of four diploid watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai cultivars was examined. Germinating embryos in darkness significantly improved the number of explants that produced harvestable shoots during the 6 week incubation period on shoot regeneration medium under a 16-h photoperiod. The percentage of explants with shoots more than doubled 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 explants with shoots was not significantly improved for `Minilee' by pretreating seedlings in darkness. This study demonstrates that optimal shoot regeneration can be obtained by germinating embryos in darkness before preparing cotyledon explants. This revised version was published online in June 2006 with corrections to the Cover Date.