IN-VITRO SHOOT PROLIFERATION RATES OF THE ROSE CV (HYBRID TEA) DR VERHAGE, AS AFFECTED BY APICAL DOMINANCE REGULATING SUBSTANCES

The effects of three shoot tip pinching compounds incorporated into th e nutrient medium and of the successive reculture technique on in vitr o shoot proliferation of rose, cultivar 'Dr. Verhage', were studied, O f the three compounds tested, methyl ester of lauric acid (MELA) was t he most effective followed, in declining order, by n-propyl-3-t-butylp henoxyacetate (M&B 25-105) and 2,3,5-triiodobenzoic acid (TIBA). MELA at 100 mg l(-1) nearly quadrupled the proliferation rate of untipped m icroshoot explants, which was comparable to the tipped controls. Succe ssive recultures of the basal clump of tissue remaining after the init ial culture, on medium free of MELA resulted in a significant increase in the total number of new shoots, compared with the tipped controls. The other two compounds also promoted branching in untipped shoots bu t were less effective, The results showed that manual tipping of expla nts can be successfully substituted by chemical tipping, thus eliminat ing unnecessary handling of plant material under sterile conditions.