Desiccation Tolerance in Bare-rooted Apple Trees Prior to Transplanting

Abstract Ten types of apple (Malus domestica L.) trees (six different scions on M.7 rootstock and four ‘Red Delicious’ scions on M.7, MM. 111, MM.106 and seedling rootstocks) were subjected to air drying for periods of 0 to 48 hr with or without 3 months of cold storage at 0°C (32°F). The kinetics of water loss during drying treatment and the transplanting survival and regrowth vigor were recorded. Both the scions and rootstocks influenced the tolerance of apple trees to desiccation stress. Among the plant materials tested, ‘Red Delicious’ on MM. 111 rootstock had the highest level of tolerance to desiccation. Three months of cold storage at 0°C (32°F) resulted in the considerable loss of tissue water, but the grafted trees survived if no further desiccation occurred prior to planting. Only ‘Red Delicious’/MM. 111 tolerated desiccation from the combination of three months of cold storage followed by a 48 hr exposure to air drying, while other scion/rootstock compound systems seldom survived. The analyses of water loss from apple trees indicated that the loss did not follow a simple first order reaction. However, there were two distinct first order water loss slopes suggesting that the loss was from two fractions of water inside plant tissues. One fraction of tissue lost water at a faster rate than the following second fraction which was slowly released from the plant tissues. There was no difference in the critical water content and rate of water loss between the tolerant trees, (i.e., ‘Red Delicious’ on MM. 111) and the others. Therefore it is suggested that trees on MM. 111 are more tolerant to desiccation because of the tolerance to water loss in the tissue.