Transgenic Clones on Field Ready Rootstock

A protocol for micrografting shoot tips harvested from in vitro shoot cultures directly to transplanted rootstock plants in the greenhouse was developed. Shoot tips of the apple (Malus domestica) cultivars Golden Delicious, Granny Smith and Fuji clone, Nagafu12, were harvested, stored in a water bath then prepared for grafting by cutting the stem immediately below the tip into a wedge shape leaving the tip approximately 3 mm (0.12 inch) long. The rootstock cultivar, Malling 9 (M.9) (M. domestica), was prepared by cutting into a young fast growing side branch to expose the cambium, creating a pocket into which the shoot tip was inserted. The cut section of the tip was oriented so as to contact the exposed rootstock cambium and was held in place by wrapping with a strip of pliable plastic fi lm. Two weeks later the wrapping was loosened and the grafted branch cut back. Side branches of the rootstock were not removed until later in order to support rootstock growth. The scion shoots developed into nursery whips suitable for transplanting to a screen house or fi eld after 2 months. The protocol proved to be a simple effi cient way to rapidly grow nursery trees from tissue culture clones developed in genetic modifi cation experiments and was used to propagate several hundred plants. Grafting success was often 100% but was reduced if quality of shoot tips was poor due to injury indicated by brown tip color. The protocol eliminates the steps of rooting, acclimatizing and growing shoots into plants to serve as a scion wood source.