IMPROVED ORGANIC AND LOW-INPUT APPLE PRODUCTION USING ROOTSTOCKS TOLERANT TO WEED COMPETITION

In organic and low-input, sustainable apple (Malus domestica) production, tree development during the first three years after planting is often inadequate. Using traditional vigorous rootstocks to overcome this problem is not a solution for modern fruit production because yield sets in too late and final tree size is too big to produce economically. In 1998, we installed a trial at three sites in Switzerland to test 10 rootstock selections grown under 100% organic, extensive management: Czech rootstocks J-TE-G, J-TE-E, J-TE-F and J-OH-A; Budagovsky 9, Cepiland (Pajam® 2), P22, Supporter 2, M.7 (as a reference for an over-vigorous rootstock) and M.9 Fleuren 56 (as a reference for a modern dwarfing rootstock) with three scab resistant cultivars: i) ‘Resi’; low vigour, small fruit; ii) ‘Resista’; vigorous, poor branching; iii) ‘Ariwa’; balanced vigour, well branched. We assessed growth vigour, branch development, yield, fruit size and quality, suckers and burr knots, plant health, and nutrient uptake in both leaves and fruit. We found highly significant influences of rootstock and variety and regular interactions of rootstock with cultivar. After the 6^th growing season, highest total cumulative yields occurred with M.7 (27.8 kg/tree), Supporter 2 (19.8 kg/tree) and Cepiland (15.0 kg/tree) whilst lowest occurred with J-TE-F (6.9 kg/tree). The rootstock-induced differences between lowest and highest yield was 416%. With cumulative relative yield (kg per mm stem-circumference) M.7 and Supporter 2 performed best (2.13 and 1.94 kg/mm), followed by Fleuren 56 and Cepiland (both 1.68) and P22 (1.52) with the difference between lowest and highest rootstocks being 231%. In 2005, with 153 mm stem circumference M.7 was 29% more vigorous than Supporter 2 (118), Cepiland (105) or Fleuren 56 (83). The tree vigour of Supporter 2 was judged almost ideal getting an average of 99 rating points (where 100 points would be the optimum) as well as in terms of feathering and leaf condition. Relating to nutrient uptake and fruit quality, significant differences were frequently found that correlated with tree performance and fruit quality. Under Swiss conditions, Supporter 2 seems to be a good alternative to M.9-type rootstocks for low-input and organic apple production.