THE INFLUENCE OF SUMMER PRUNING AND FRUIT CROPPING ON GROWTH, CARBOHYDRATE AND NUTRIENT ELEMENT STATUS OF APPLE TREES

'Jonathan'/M26 apple trees were summer pruned in August of 1978-1980 by removal of all current-season shoots longer than 10 cm. Control trees were dormant-pruned. Cropping treatments were established by allowing trees to retain a full crop or by defruiting them in June of 1979 and 1980. Length of terminal shoot regrowth was reduced 82 and 76 percent by summer pruning in 1979 and 1980, respectively. Terminal shoots produced the year following pruning were 55 and 62 percent longer on summer pruned trees than on controls in 1979 and 1980, respectively. Summer pruned trees with a full crop had 13 percent shorter average terminal shoot length than defruited trees in 1979, but cropping had no effect in 1980.;Canopy openness to light penetration was increased after summer pruning as measured by hemispherical lens photography. Summer pruned trees intercepted greater amounts of photosynthetic active radiation in the bottom two-thirds of the canopy.;Fruit yield per tree was reduced by summer pruning, but yield per canopy volume was not affected. Average fruit size was decreased by summer pruning in 1979 but increased in 1980. Maturing fruits on summer pruned trees had higher rates of ethylene evolution during the three weeks prior to harvest in 1980. Fruit soluble solids were reduced in 1979 and 1980, but flesh firmness was not affected. Fruit color was increased in 1978 and 1980 but not in 1979.;Summer pruning did not generally influence total nonstructural carbohydrate content. Sorbitol, glucose and fructose levels were increased as amounts of shoot removal increased in comparison to unpruned trees. Mineral levels of leaves were not generally affected.;Trees with a full crop had a smaller annual increase in trunk cross-section than defruited trees, but summer pruning had no effect. Summer pruning minimized the increase in tree canopy dimensions and resulted in 43 percent less canopy volume than control trees in 1979 and 1980. Fruit set was not affected by pruning or cropping treatments, but summer pruning hastened anthesis.