EARLY PERFORMANCE OF FOUR APPLE CULTIVARS GRAFTED ON THE MICROPROPAGATED OTTAWA THREE ROOTSTOCK AND TRAINED IN TWO SYSTEMS
In experimental plots established in 1989, `Spencer', `Empire', `MacSpur', and `Lobo' trees grafted on the in vitro-propagated Ottawa 3 (0.3) rootstock were trained in the triple axis and in the slender spindle systems. They were planted at 5 (between rows) × 2.04 m and laid out in a split plot array with four replicates. There were five trees per subplot unit. All trees were trickle-irrigated every year. Fruit thinning was chemically done for the first time in 1993. Trees from this experiment came into bearing in 1991, and their total cumulative yield was significantly superior in the case of trees of the Spindlebush system. Since no interactions were found, we cannot conclude that any given combination is better than the others. `Lobo', which has averaged nearly 21 tonnes/ha per tree, was best in terms of total cumulative yield and also in terms of yield efficiency. `MacSpur' and `Empire' were the second best ones in yield efficiency, and `Spencer' was significantly lower. Fruit size was very good for all combinations in 1993. At their fifth-leaf stage in 1993, the yield of `Empire' trees from this experiment was higher by an average of more than 1 kg per tree than that of comparable trees of conventionally propagated O.3 trees planted in adjacent test plots. The tree vigor of the micropopagated O.3 trees was better than that of the conventionally propagated ones as revealed by the trees' trunk and canopy development. However, a few trees exhibited slight burr-knot growth on their trunk. This has never been observed on the conventionally propagated O.3 rootstock.