PHYSIOLOGICAL AND PHENOLOGICAL RESPONSES OF APPLE TREES TO ARTIFICIAL REDUCTION OF THE GROWTH PERIOD FROM HARVEST TO LEAF FALL
New Zealand has a longer growth interval from harvest until natural leaf fall than many other apple-growing regions in USA and Europe. An extended period for the accumulation of carbohydrate reserves within the tree may be an underlying reason why New Zealand apple orchards readily achieve very high crop yields compared with other climates. To determine the effects that timing of autumn leaf loss may have on apple tree phenology, growth, flowering and crop potential in the following season, a series of artificial leaf removal treatments was established. The results from the first year following treatment application are presented in this paper. Either 100% (complete defoliation) or 50% (half-defoliation) of the leaf area of ‘Royal Gala’ apple trees on M.9 rootstock was removed 10 days (early defoliation) or 31 days (late defoliation) after completion of crop harvest. Non-defoliated control trees underwent natural leaf fall 12 weeks after harvest. One week following early defoliation, net photosynthesis of bourse shoot leaves was 20% higher from half-defoliated trees compared with controls. If defoliation treatments were delayed until 31 days after harvest, less difference in bourse shoot leaf net photosynthesis between half-defoliated and untreated trees could be detected, when measured three weeks after defoliation. Time to 50% natural leaf fall on half-defoliated trees occurred approximately 6 days later than on untreated trees. Bud break in the following spring was delayed 4–6 days by autumn defoliation treatments. On trees which underwent early complete defoliation, king full bloom was 4–6 days later than on untreated trees. Early complete defoliation treatments reduced initial and final fruit set compared with other treatments. Defoliation treatments did not significantly reduce spur leaf number, bourse leaf number or bourse leaf area. However on trees completely defoliated early, individual spur leaf area was reduced to 4.9 cm2 compared with 6.4 cm2 on untreated trees. During this subsequent growing season there was also a reduced rate of increase in trunk cross-sectional area on trees which were completely defoliated early. Early defoliation treatments reduced yield via reduced fruit size not reduced fruit numbers.
Tustin, D.S., Stanley, C.J. and Adams, H.M. (1997). PHYSIOLOGICAL AND PHENOLOGICAL RESPONSES OF APPLE TREES TO ARTIFICIAL REDUCTION OF THE GROWTH PERIOD FROM HARVEST TO LEAF FALL. Acta Hortic. 451, 383-404
defoliation, flowering and fruit set, fruiting potential, Malus domestica (Borkh.), photosynthesis