N.M.R. Vattiprolu, D.J. Woolley, B.M. van Hooijdonk
Mechanisms of vigour control by dwarfing rootstocks are poorly understood. For apples, it is hypothesised that dwarfing of the scion by rootstocks may result from modified transport of growth hormones. Reduction in indole-3-acetic acid (IAA), transported through the stem tissue of a dwarfing rootstock to the root, may decrease the export of cytokinins and gibberellins from root to shoot in the xylem vasculature. Recent studies reported that lower amounts of gibberellins supplied from the roots of a dwarfing apple rootstock limited the final mean length and node number of the primary shoot, whilst a reduced supply of root-produced cytokinins may limit the number of secondary shoots formed on the scion. This suggests that dwarfing of the scion may be controlled by shoot-root-shoot signalling of endogenous hormones. Therefore, the aim of the present study was to implement the present understanding of hormonal shoot-root-shoot signalling and to elucidate whether a generalised signalling mechanism existed in other economically important fruit crops such as kiwifruit. To investigate shoot-root-shoot signalling in kiwifruit vines, the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) was applied to the primary shoot, just above the first node, and vines were grown in either a small 1 L container for root restriction (RR) or a large (10 L) container volume. The NPA treatment reduced the primary shoot length but increased the formation of secondary shoots. The effect of NPA+RR appeared to be additive since the reduction in the length of the primary shoot due to NPA or RR was 16 or 31%, respectively, when compared to the control. The combined effect of NPA+RR was to reduce the length of the primary shoot by 45%, and to reduce secondary shoot formation by 80% compared with the control vines. Lower vigour of NPA+RR-treated vines was associated with a 50% reduction in the weight of winter prunings. These results will be discussed in terms of alternative hormonal control mechanisms related to vegetative vigour.
Vattiprolu, N.M.R., Woolley, D.J. and van Hooijdonk, B.M. (2011). HORMONAL CONTROL OF VEGETATIVE VIGOUR IN KIWIFRUIT VINES. Acta Hortic. 913, 425-431
DOI: 10.17660/ActaHortic.2011.913.57
N-1-naphthylphthalamic acid, root restriction, cytokinins, gibberellins, indole-3-acetic acid, rootstocks, pruning weight

Acta Horticulturae