In vitro propagation of watermelon

A 3-stage, in vitro propagation system for diploid watermelon (Citrullus lanatus (Thumb.) Matsum. and Nakai) has been developed which is also applicable to the economic production of triploid (seedless) watermelon transplants.Stage I involves the stimulation of axillary-bud development from excised seedling shoot tips (1–3 mm) by a high cytokinin (K)/low auxin (IAA) ratio (4.6 μmol/l K 0.28 μmol/l IAA) on a modified Linsmaier and Skoog medium. An average of 4.5 axillary shoots of sufficient size to subculture (> 15 mm) were obtained from each explant in 5 weeks. These shoots were induced to root during 3 weeks subculture on Stage II medium containing 11.5 μmol/l IAA. Well-rooted plantlets were successfully transplanted to a 1 : 1 peat : sand (v/v) substrate and gradually “hardened-off” to greenhouse conditions (Stage III) for 3 weeks, after which they could be transferred to field conditions.Alternatively, axillary shoots from Stage I could be returned to fresh media with 9.3 μmol/l K and 0.28 μmol/l IAA, where an average of 10.3 axillary shoots could be obtained after 5 weeks.Cost estimates for producing 10 000 finished transplants per week project an approximate cost of 16 dollar cents per transplant.