PARTITIONING SOURCES OF ROOTING POTENTIAL IN PLUM HARDWOOD CUTTINGS

Rooting of leafless winter hardwood cuttings of the plum rootstock Pru nus insititia 'Pixy' increased as the location from which the shoots w ere taken from within specially grown stockplants decreased in height above ground, associated with a parallel reduction in shoot thickness. However, the actual height of the least-ready-rooting crown cuttings had no effect on rooting, suggesting that relative rather than absolut e position is important. Rooting was unaffected by bark-ringing and tr unk incision distal to the shoot position, suggesting that such treatm ents did not interfere with a basipetally translocated root promotor w hich might have accounted for improved rooting of cuttings in the lowe r parts of the hedge. The rooting of crown cuttings above a bark ring was reduced considerably compared with that of cuttings from normal bu shes, and this was associated with increased thickness of shoots dista l to the ring. Delaying pruning in spring until after growth had start ed resulted in thinner crown shoots compared with those from plants pr uned normally while dormant, and the rooting of these thinner crown sh oots was much higher than that of the normal crown cuttings. It was sh own by covariance analysis that shoot thickness accounted for part of the rooting response but could not account for the total effect due to shoot position within the bush, ringing, or time of pruning. Competen ce to root appears to develop independently in individual shoots, modi fied by a shoot thickness factor which favours the subordinate shoots induced in the shoot hierarchy of severely pruned hedges.