IN VITRO PROLIFERATION COMPETENCE OF PROTOCORM-LIKE-BODIES FOR DIRECT INDUCTION OF SHOOT BUDS FOR MULTIPLICATION OF VANDA 'ROBERT'S DELIGHT'

摘要

A comparative study between in vitro propagation via protocorm-like-bodies (PLBs) and direct shoot buds showed that commercially viable mass multiplication of Vanda hybrid 'Robert's Delight' can be achieved through PLB propagation. Different media, plant growth regulators (PGRs), and explants from mature orchids, keikis, and axenic plants were studied for establishment of effective induction and proliferation protocol for mass multiplication the Vanda hybrid. The leaf base explants from mature plants and keikis (59.4%) could develop a mean of 18.2 direct shoot buds in 8 weeks when cultured in half-strength Murashige and Skoog (MS) medium with 1.5 mg l(-1) Thidiazuron (TDZ) and 20% coconut water (CW) but there was high phenolic exudation and necrosis of explants both in induction and proliferation media. Repeated bimonthly subculturing in proliferation media did not produce effective multiplication and the shoot buds differentiated to shoots producing about 70 plantlets per leaf base explant in a year. When in vitro derived shoot tips were used as explants, 68.4% of the axenic shoot tips formed both callus-free PLBs and shoot buds in half-strength MS medium supplemented with 1 mg l(-1) TDZ and 10% CW as early as 5 weeks resulting in 31.5 shoot buds in 8 weeks. Proliferation of secondary PLBs was highest in New Dogashima Medium (NDM) devoid of PGRs and sugar, reaching 69.2 PLBs per shoot tip in another 8 weeks. Thus maximum clonal output was possible only through the induction and proliferation of PLBs. This protocol is highly efficient and can be used profitably for commercial propagation of Vanda orchids.