Effect of interstock bridge grafting (M9 dwarfing rootstock and same cultivar cutting) on vegetative growth, reproductive growth and carbohydrate composition of mature apple trees

Four apple cultivars, Granny Smith, Cox's Orange, Gala and Oregon Red Delicious on rootstock MM106, M793 or Northern Spy were interstock bridge grafted with M9 dwarfing rootstock or same cultivar cuttings to investigate the effect on vegetative, reproductive and biochemical changes and fruit quality at harvest in different apple cultivars. Controls were also left with no interstock treatment. In general bridge grafting reduced shoot growth (up to 20%), increased floriferousness, changed carbohydrate (CHO) level and increased yield (up to 30%) with the greatest effects in the second season. The treatment did not significantly change mean fruit weight, fruit length to diameter (L/D) ratio or flesh colour in first season, while in the second season there were significant differences in these apple quality measures. Seed number and brix value at han est from both treatments were significantly increased in both seasons. Flesh firmness also showed significant increases in both seasons. The M9 bridge and same cultivar interstocks were generally similar in effect though occasionally the M9 had a greater effect. Interstock bridge grafting of mature apple trees may be a viable method of reducing growth and improving yield. (C) 1999 Elsevier Science B.V. All rights reserved.