Apple rootstock evaluation for apple replant disease

Twenty nine rootstocks from the Cornell Geneva breeding programme, some Budagovski rootstocks and M.9 T337 and M.26 EMLA as control were screened for apple replant disease (ARD) tolerance at NYSAES Geneva, New York in 2008. Bench grafted rootstocks were planted in pots with two types of soil - heavy clay and sand prepared from old orchard sites. Half of each soil type was pasteurised. Weight of planting material before planting was recorded in order to calculate total mass increase after the growing season. During the growing season dynamics of scion growth, number of feathered trees, number of branches and total branch length was recorded at biweekly intervals. At the end of the season plant, scion and root weight, as well as absolutely dry weight of whole plant, scion, rootstock shank, large roots and fine roots were recorded. Though better tree development occurred in clay rather than in sand, soil type did not influence rootstock tolerance to ARD. Interactions of rootstock and soil type were recorded only for trunk diameter. Evaluation of growth dynamics shows earlier growth termination in both ARD soils. Clear ARD effects were noticed in the number of feathered trees and total branch length. Three times more feathered trees occurred in pasteurised clay soil than in untreated replant clay soil. Scion dry weight appears to be the most reliable measure of rootstock tolerance to ARD. A high number of Geneva rootstocks including G.30, G.11, G.202, G.41 and G.65 showed tolerance to ARD conditions. Rootstocks CG.4002, M.9T337, B.9, CG.7707, CG.6040, B.490, CG.3007 and M.26EMLA were the most sensitive to ARD.