Minimizing the hyperhydricity associated with in vitro growth and development of watermelon by modifying the culture conditions
Hyperhydricity or glassiness is considered as a frequent problem associated with the in vitro growth and development of watermelon (Citrulus lanatus, cv. Giza 1). Explants were cultured on MS (Murashige and Skoog, 1962) medium containing 6-bensyladenine (BA), kinetin (Kin) or thidiazuron (N-phenyl N 1,2,4-chlorophenoxyacetic acid) (TDZ) each applied at 0, 0.25, 0.5, 1, 2 and 4 mg L-1). The highest number of regenerating shoots per explants MS medium containing 0.5 mg/l TDZ proved to be the most efficient in the induction of adventitious organogenesis, while BA applied at 2 mg L-1 was the most efficient in axillary shoot proliferation. Increase in BA concentration (above 2 mg L-1) gave multiple shoots and led to more pronounced hyperhydricity, while the use of 1 mg L-1 facilitated single-shoot growth with relatively lower incidence of hyperhydricity. Substitution of agar (10 g L-1) with gelrite (4 g L-1) in the medium as well as improving vessel aeration reduced occurrence of hyperhydricity. Provision for aeration was relatively superior to other approaches, but it led to faster dehydration of medium and limited growth of cultures. Rooted shoots produced on half strength MS medium with aeration, and 0.5 mg L-1 indole 3-butyric acid (IBA) were transferred to pots and acclimatized in green-house with a survival rate of 80%.
Keywords: Aeration, gelling agents, hyperhydricity, in vitro, rooting, plant growth regulators, ventilation, watermelon