Differences among rootstock cultivars in late wood discoloration and freezing tolerance in apple trees [Malus pumila] grafted onto dwarfing rootstocks

Differences of the late wood discoloration were investigated for apple trees (Malus domestica Borkh.) grafted onto dwarfing rootstocks. In dissection of adult trees of 'Fuji' and 'Jonagold' grafted onto JM1 and JM7, the late wood discolorations differed with the rootstocks. One year old trees of 'Mishima-Fuji' grafted onto three rootstock cultivars, JM7, M.9, and M.26, were frozen to observe browning in the cambium and its surroundings and to measure the rate of damaged cells in the bark. The browning degree increased as the treatment temperature decreased. The rate of damaged cells decreased in that order M.9, JM7, M.26, especially in the rootstock part. These results indicated that there were differences among rootstock cultivars for the late wood discoloration and the rate of damaged cells, which affected the degree of freezing injury under the field condition.