Abstract
Early fruit drop of ‘McIntosh’ apple was enhanced by night temperatures of 25°C. The relationship between this fruit drop and shoot growth was investigated.
Shoots grew more vigorously as the temperature rose, with fruit drop occurring simultaneously. It was concluded that early drop of fruit occurred because of competition with shoots for reserve substances. Shoot growth was inhibited by spraying with N-dimethylaminosuccinamic acid (SADH) and fruit set was increased. Shoot tipping treatment also increased the number of fruit retained through the “June drop” period. These two treatments increased fruit set by reducing competition between fruits and shoots.
Spraying with BA markedly increased the number of shoots and the frequency of fruit drop. The increase in early drop of fruit was probably due to severe competition from shoots which was enhanced by BA.
Spraying of GA4/7 increased fruit set at 50, 100 and 500ppm, whereas shoot growth was promoted at 500ppm of GA4/7, but inhibited at 50 and 100ppm of GA4/7.
