ROLE OF GROWTH-REGULATORS IN IN-VITRO RHIZOME GROWTH OF POTATO

Disinfested, etiolated medial segments of potato (Solanum tuberosum L,) sprouts cv. Katahdin with two axillary buds were placed on Murashige and Skoog (MS) medium in clear plastic culture boxes, Basal ends of explants were inserted into MS medium containing BA at 2 mg . liter(-1). Nine treatments, composed of factorial combinations of GA, at 0, 0.2, and 2 mg . liter(-1) and IAA at 0, 0.3, and 3 mg . liter(-1), were imposed, These were applied via small agar cylinders placed on the apical cut surface of each segment. Regardless of the presence of cytokinin and auxin, no rhizomes developed after 3 weeks in culture without a supply of GA(3), Number and length of primary and secondary rhizomes increased with an increase in GA(3) concentration in the agar cylinder from 0 to 2 mg . liter(-1). Rhizome initiation and development appear to be controlled by coordinated participation of endogenous plant hormones during the early events leading to tuber development. Chemical names used: 2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10-carboxylic acid 1->4 lactone (GA(3)); indole-3-acetic acid (IAA); N-(phenylmethyl)-1H-purin-6-amine (BA).