MICROPROPAGATION OF ROSES - THE BENEFITS OF PRUNED MOTHER-PLANTLETS AT STAGE-II AND A GREENHOUSE ENVIRONMENT AT STAGE-III

Opportunities for improving cost-effectiveness in the micropropagation of roses were sought. The roses 'Frensham' and 'Mountbatten' were pro pagated during Stage II from cuttings obtained by pruning ''mother-pla ntlets'' at intervals of two weeks. The size of the mother-plantlets w as controlled by regular pruning and by splitting after 22 weeks. The method was more economical in terms of space in the growth room, labou r and culture medium that the more conventional method of subdividing plants every four weeks. More cuttings were obtained if the agar-solid ified medium was overlaid with liquid medium. After 18 weeks on the ov erlaid medium, an estimated 14 propagules could be obtained every two weeks per mother-plantlet of 'Frensham' and 11 of 'Mountbatten' if the culture medium was renewed every ten weeks. Propagules from Stage II were cultured at Stage III on cellulose plugs in culture vessels with a gas-permeable membrane in the lid. The effect of high irradiance in a greenhouse location was contrasted with the lower irradiance in a gr owth room when plants were cultured on either Murashige and Skoog medi um (1962) supplemented with sucrose (30 g l(-1)), or a hydroponic medi um without sucrose. High irradiance increased the fresh weight of plan tlets, the proportion of root to shoot growth and leaf expansion. Sucr ose-free medium increased leaf area. Effects of these cultural conditi ons were still evident four weeks after transfer of propagules to comp ost.