NOVEL PLANT GROWTH REGULATOR DELIVERY SYSTEMS FOR IN VITRO CULTURE OF HORTICULTURAL PLANTS

Several alternative methods other than via the medium for providing plant growth regulating chemicals to plant tissues cultured in vitro have been investigated. Spraying the stock (mother, or donor) plant with cytokinins has resulted in similar shoot proliferation to that induced by inclusion of the same cytokinin in the medium. Similar responses were obtained when the explant tissue was soaked in cytokinin solutions prior to explant placement in the culture vessel. Using this method, concentrations of 100 to 800 mg/l benzyladenine (BA) were shown to be effective for petunia leaf segment culture.

Forcing solutions containing sucrose and 8-hydroxyquinoline citrate, similar to solutions employed for enhancing cut flower longevity, have been demonstrated to improve quality of explants taken from softwood growth of several woody species for in vitro culture. Both BA and gibberellic acid (GA₃) have been shown to influence such softwood growth when they were included in the forcing solution. Subsequent stimulation of in vitro shoot growth and proliferation from explants produced in this fashion have been recorded. Several deciduous genera have been demonstrated to respond favorably to such treatment, including Castanea, Dirca, Philadelphus, Aesculus, and Amelanchior. It is proposed that forcing solutions offer another highly useful approach for manipulating responses of plant tissues cultured in vitro.