Effect of cytokinins on organogenesis and callus induction in cotyledonary explants of tomato (Lycopersicon esculentum Mill.)

The relative effectiveness of two cytokinins (6-benzylaminopurine (BA) vs. zeatin (Z), at 6 different levels viz. 0, 1, 2, 5, 10 or 15 muM on shoot, root and callus induction, using cotyledonary explants of tomato cv. 'Red Coat' was examined. Cultures were transferred to cytokinin-free medium after 4 weeks. Both BA and zeatin (Z) were found to be effective for shoot induction with a significant effect (P less than or equal to 0.001) of concentration. Significant (P less than or equal to 0.001) interaction between the type and concentrations of cytokinins was observed for number of shoots produced per explant. BA at 5 muM produced the maximum number of shoots (5.60 explant(-1)), while zeatin at 1 and 2 muM produced significantly (P less than or equal to 0.05) longer shoots with mean shoot length of 18.2 and 13.83 mm, respectively. Both BA and Z at higher concentrations (5 muM to 15 muM) induced callus in a large number of explants (53.3 to 100%) and the callus size was significantly (P less than or equal to 0.001) bigger with BA (12.6 vs. 6 mm) application. A small percentage of cultures (17%) produced roots, on transfer to cytokinin-free medium. However, root induction was not significantly influenced by the type or concentration of cvtokinin used. As BA induced higher amounts of callusing, a potential danger of somaclonal variation suggesting that zeatin at higher concentration (15 muM) might be the most suitable for regeneration of the 'Red Coat' variety.