EFFECT OF REPEATED SPRAYS OF 6-BENZYLADENINE ON THE FORMATION OF SYLLEPTIC SHOOTS IN APPLE IN THE FRUIT-TREE NURSERY

In 1992 growing shoot tips of nursery trees of the apple cultivar 'Red Boskoop' on rootstock M.9 (budded August 1991 at 15 cm) were sprayed four or eight times at weekly intervals with 50, 100, 200, or 400 p.p. m. 6-benzyladenine (BA), starting when scion length was 35 cm. The eig ht BA treatments were compared with untreated controls and with plants sprayed once with the standard branching agent Promalin, a mixture of equal quantities of BA and GA(4+7) (gibberellins A(4) and A(7)), 1000 p.p.m. of each hormone being used. All sprays contained the wetter Tw een 20 at 1% v/v. Except for 50 p.p.m., all BA treatments increased th e number of laterals and the more so the higher the concentration and the number of sprays. Eight sprays with 200 and 400 p.p.m. BA and four with 400 p.p.m. BA gave more laterals than a Promalin application. Th e most active BA treatments enlarged the zone of lateral emergence by 50 cm. The treatments did not or hardly affected stem diameter or leng th and there was no temporary slowing down of the growth of the stem t ip that could explain the extra development of laterals. Neither Proma lin nor the 50 or 100 p.p.m. BA sprays affected flower-bud formation, but continuing the use of higher BA concentrations in July by spraying eight times proved detrimental.