PRIMING ABIOTIC FACTORS FOR OPTIMAL HYBRID CYMBIDIUM (ORCHIDACEAE) PLB AND CALLUS INDUCTION, PLANTLET FORMATION, AND THEIR SUBSEQUENT CYTOGENETIC STABILITY ANALYSIS

Abstract Abiotic factors affect the induction of PLBs and callus in hybrid Cymbidium Twilight Moon ‘Day Light’. The initiation and proliferation of new PLBs and callus could be achieved on NAA and kinetin, supplemented at 0.1 mg l −1 each, respectively, both within 45–60 days. Bacto agar was found to be the most suitable solidifying agent for PLB induction, although a higher shoot fresh weight was obtained on Gelrite; a pH 5.3 was optimal while pH 4.5 caused 100% explant necrosis; coconut water, when supplied at 10–20% (v/v) resulted in a significant increase in the number of PLBs formed per PLB segment (23.1 versus 14.6 in controls) while a massive (almost four-fold) increase in fresh top weight occurred when PLB explants were placed in liquid culture, as a result of hyperhydricity; Fe-EDTA (1 mg l −1 ) and activated charcoal (1 g l −1 ) stimulated total fresh weight and PLB formation in the presence of PGRs; PLB formation decreased but total fresh shoot weight increased with the addition of niacin or myo -inositol, both vitamins. Dark-grown PLB-induced plants were etiolated and had longer internodes and higher fresh weight than light-grown control plants at 45 μmol m −2  s −1 ; at 15 μmol m −2  s −1 shoots were slightly etiolated, fragile, and PLB formation was scarce. RAPD and mtDNA analysis of all resultant PLBs, callus or plants showed them to be genetically identical, with comparable chlorophyll contents. Despite the detection of cytological variation between different plant parts, little variation resulted from abiotic factor treatment.