PERFORMANCE OF ELITE CORNELL GENEVA APPLE ROOTSTOCKS IN LONG-TERM ORCHARD TRIALS ON GROWERS FARMS

A series of replicated trials on growers farms in New York State were begun in 1991 to evaluate the Cornell-Geneva series of apple rootstocks which have been bred for tolerance to fire blight and Phytophthora root rot, high yield efficiency and good tree survival. Results from the on-farm trials have helped identify which rootstock clones should be commercialized and which should be eliminated from the breeding program. Among dwarfing rootstock candidates that are similar in size to M.9, CG.3041 and G.16 have shown the greatest yield efficiency and have exceeded the performance of M.9. CG.3041 has shown excellent tolerance to fire blight and has also shown good cold hardiness in test winters. In one trial with Gala, it has shown some tendency for brittleness of the graft union, but in all trials it has had better survival than M.9. Among dwarfing rootstock candidates that are similar to M.26, both CG.5935, and CG.4202 have performed well exceeding the yield performance of M.26 and both have had excellent tolerance to fire blight. They have also shown some tolerance to replant disease. Among semidwarfing stocks, G.30 and CG.6210 have performed well exceeding by several fold the yield performance of M.7. Both have shown excellent fire blight resistance and good cold hardiness. G.30 has shown graft union brittleness with Gala which makes tree support mandatory for this semidwarfing stock. CG.6210 has shown better graft union strength, but has had only moderate tree anchorage in some locations. It will also require tree support.