A STUDY OF THE EFFECT OF GROWTH-REGULATORS AND TIME OF PLANTLET HARVEST ON THE INVITRO MULTIPLICATION RATE OF HARDY AND HYBRID TEA ROSES

The effect of benzyladenine (BA) (0, 0.5, 2.5, 5 and 10 ppm), naphthaleneacetic acid (NAA) (0, 0.005, 0.01, 0.1 and 1 ppm) and time of proliferation (six, eight and ten weeks) on the optimum multiplication conditions for four Rosa hybrida cvs Champlain, John Franklin, John Paul II and Landora were studied. BA and NAA both had a significant effect on the proportion of viable plantlets and on multiplication rates while low or high concentrations of these growth regulators in the medium generally caused a reduction of plant material. The optimum multiplication rate also varied with cultivar and time. Concentrations of NAA above 0.1 ppm decreased the multiplication rate significantly for two of the cultivars. There was no consistent response between multiplication rates and cultivars to concentrations of BA, NAA of even the time of culture, and it is therefore recommended that each of these variates be determined for each cultivar to obtain optimum plantlet yield.