ARCHITECTURAL DEVELOPMENT OF ´ROYAL GALA´ APPLE SCIONS IN RESPONSE TO ROOTSTOCK, ROOT RESTRICTION, AND BENZYLAMINOPURINE
Dwarfing apple rootstocks and practices like root restriction may decrease scion vigour by reducing cytokinin export from the root to the shoot system. To understand the role that cytokinin may have in dwarfing of the scion, Royal Gala apple scions grafted onto dwarfing, semi-vigorous, and vigorous rootstocks (M.9, MM.106, and MM.793, respectively) were grown in two root volumes (8 and 45 L) and treated with repeated applications of the synthetic cytokinin benzylaminopurine (BAP). Scion architecture was measured to determine how the dwarfing rootstock and root volume treatments altered growth, and whether growth effects could be reversed with exogenous cytokinin supplied to the scion. The 8 L root volume and the M.9 rootstock both decreased scion height, node number, the total length of laterals, total growth, and bud break along the main axis. With the exception of scion bud break and lateral number, exogenous BAP did not overcome reductions in growth caused by M.9 and the 8 L root volume. The predominant effects of exogenous BAP were to increase bud break and lateral number. M.9 in response to BAP produced 13 and 10 % more axillary bud break than MM.106 and MM.793 scions, respectively. These preliminary results indicate that a reduced root supply of cytokinin could be involved in the development of dwarfing scion architecture, but the role of cytokinin at the scion is probably specific to the regulation of bud break, lateral production, and the allocation of growth between plant axes. Differences in interactions with BAP indicated that other factors in addition to root volume were involved in rootstock effects.
Hooijdonk, A., Woolley, D., Warrington, I. and Tustin, S. (2006). ARCHITECTURAL DEVELOPMENT OF ´ROYAL GALA´ APPLE SCIONS IN RESPONSE TO ROOTSTOCK, ROOT RESTRICTION, AND BENZYLAMINOPURINE. Acta Hortic. 727, 561-568
Malus × domestica, cytokinin, vigour, bud break, lateral shoots