THE EFFECT OF AUTUMN AND SPRING TEMPERATURE ON FRUIT-SET AND AN THE EFFECTIVE POLLINATION PERIOD IN APPLE AND PEAR

Under completely controlled conditions fruit set and the effective pol lination periods (EPP) of apple cultivar 'Golden Delicious' and pear c ultivar 'Doyenne du Comice' were evaluated as affected by autumn tempe rature (9 degrees C and 24 degrees C, apple; or 10 degrees C, 14 degre es C, 17 degrees C and 22 degrees C, pear) in combination with two spr ing temperatures (13 degrees C and 19 degrees C, apple; or 13 degrees C and 17 degrees C, pear). In apple the low-temperature period started just after the end of bloom, in pear the two temperature treatments w ere already applied in February when the trees were still in rest. In apple and pear there was no effect of the autumn temperature on fruit set. In apple, although bloom temperature was the same, the EPP was ex tended when the temperature was lowered just after bloom, resulting in a better fruit set in that treatment. There was no severe fruit drop ('June drop') between 3 and 6 weeks after full bloom in apple. In pear , fruit set was clearly lower at 17 degrees than at 13 degrees C; the length of the EPP was 4-6 days at 13 degrees C against 2-4 days at 17 degrees C. A marked fruit drop occurred between 3 and 6 weeks after bl oom in pear. The data are discussed in terms of a differential effect of temperature on ovule longevity and rate of pollen tube growth.