Reduced hyperhydricity in watermelon shoot cultures using silver ions

An effective protocol for adventitious shoot regeneration with reduced hyperhydricity was established from proximal cotyledon explants of Citrullus lanatus (Thunb.) cv. Arka Manik. The highest frequencies of shoot regeneration (100%) and shoots per explant (13.13 +/- 0.29) occurred in Murashige and Skoog (MS) medium supplemented with 8.88 mu M 6-benzylaminopurine and 2.85 mu M indole-3-acetic acid. The proportions of adventitious shoots that were hyperhydric ranged from 8.3 to 35.3%. To reduce the occurrence of hyperhydric shoots, shoot regeneration medium was supplemented with silver ions in the form of silver nitrate or silver thiosulfate. Amendment of the regeneration medium with silver ions was found to be essential during the shoot initiation and elongation phases for the development of normal shoots. Supplementation with 9.0 mu M silver nitrate resulted in the greatest reduction of hyperhydricity (to 5.8%) and increased number of shoots (to 14.20 +/- 0.36). The highest rate of rooting (80%) was observed on MS medium supplemented with 4.92 mu M indole-3-butyric acid, and rooted shoots from this treatment showed 3.97 +/- 0.16 roots/shoot. Over 85% of the regenerated plants survived acclimatization in red soil:sand (1:1 v/v) and transferred to soil mixtures viz, garden soil, farmyard soil, and sand (1:1:1, v/v/v). This protocol describes the positive influence of silver ions in reducing the hyperhydricity of watermelon shoot cultures and thus could be used for genetic transformation protocols.