GROWTH AND PERFORMANCE OF 4 APPLE CULTIVARS ON M.26 AND MARK ROOTSTOCKS, WITH OR WITHOUT PREPLANT MINERAL NUTRIENTS

To evaluate the interactions between cultivar and rootstock, four appl e (Malus domestica, Borkh.) cultivars, 'Pioneer Mac,' 'Marshall McInto sh,' 'Ginger Gold' and 'Empire' on two rootstocks, M.26 and Mark, were planted in a split-plot design. After five years,'Pioneer Mac' and 'G inger Gold' had larger trunk cross-sectional area (TCSA) on M.26 than on Mark. 'Marshall McIntosh' and 'Empire' had larger TCSA on Mark than on M.26. Precocity, expressed as both number of flower clusters and y ield was greater for trees on Mark for all cultivars except for 'Ginge r Gold,' which had greater newer cluster numbers and yield on M.26. Fr uit size was variable from year to year, depending on crop load, howev er 'Pioneer Mac' and 'Ginger Gold' usually produced the largest fruit, while 'Empire' consistently produced the smallest fruit, 'Ginger Gold ' appears to be incompatible with Mark. The results of this study demo nstrate that cultivar x rootstock interactions can be significant and need to be considered when rootstock and planting density recommendati ons are made.