Influence of the Cytokinin, 6-Benzylamino-9-(Tetrahydropyran-2-yl)-9H-Purine,on the Growth and Development of Some Ornamental Crops

Foliar sprays of the synthetic cytokin, 6-benzylamino-9-(tetrahydropyran-2-yl)-9H-purine (PBA), increased branching in carnation, chrysanthemum, poinsettia, petunia and fuchsia, which showed varying levels of tolerance. In no instance did PBA reduce plant height. Applications of PBA to carnation and chrysanthemum stimulated branching in both intact and pinched plants. Treatment a few days prior to pinching produced more uniform development of new laterals. Response to the compound was most favourable under optimum growing conditions. Under relatively poor light intensity the laterals exhibited a reluctance for continued elongation and showed marked chlorosis. Application of PBA to flower buds at an early stage of development increased both the diameter and the fresh weight of carnation flowers or chrysanthemum inflorescences when fully open. Response to the compound decreased with age of the bud at the time of treatment. In carnation the effects on size were accompanied by an increase in petal area together with an increase in the number of primary petals produced. Relatively high concentrations also induced the formation of secondary growing centres from which varying numbers of additional petals were produced. Relatively large numbers of these secondary centres within a flower resulted in an increased incidence of calyx splitting. These centres were not observed in chrysanthemum. The formation of secondary growing centres could also be induced by GA₃ and IAA. However, while these growth substances increased the diameter and fresh weight of carnation flowers, unlike cytokinins they had no apparent effect on the number of primary petals formed. Finally PBA was also observed to increase the longevity of cut flowers of carnation. This was particularly apparent at relatively low temperatures.