Issue link: https://read.dmtmag.com/i/489844
10 APRIL 15, 2015 GOOD FRUIT GROWER www.goodfruit.com Geneva rootstocks might be less vigorous in Washington. by Geraldine Warner A new rootstock trial being planted in fi ve sites in Washington State this spring should provide more insights into how Geneva apple rootstocks will perform in replanted orchards in the Pacific Northwest. The trial, being planted in Oroville, Brewster, East Wenatchee, Wapato, and Prosser, will include G.969, which has not yet been tested in the Pacifi c Northwest. The rootstock is highly resistant to woolly apple aphid and fi re blight, and has tolerance to replant disease. Cornell has ranked it as one of the most vigorous of the Geneva rootstocks released so far, similar to Malling 7 in vigor. However, results from previous trials in Washington State suggest that Geneva rootstocks tend to produce smaller trees than when grown in the eastern United States, where they were developed. Before commercial release, the Cornell rootstocks are classifi ed with the prefi x CG (Cornell Geneva) and a four- digit number, the fi rst of which denotes its relative size. So, for example, G.969 was called CG.6969 before release, meaning its vigor was rated 6 on a scale of 1 to 9. Dr. Gennaro Fazio, breeder and geneticist at the U.S. Department of Agriculture's Plant Genetic Resources Unit in Geneva, where the rootstocks were developed, said the vigor rating is just an estimate, because soil, climate, and scion can also affect rootstock vigor. Two scions are used in the new trial in Washington— Gala and Red Delicious. Tom Auvil, research horticultur- ist with the Washington Tree Fruit Research Commission, stressed that the reason for including Red Delicious is its extreme sensitivity to replant disease so that the root- stocks will be put to the ultimate test. The plots will have two treatments—fumigated and non-fumigated. The ten Geneva rootstocks in the trial include G.890 (CG.5890) and G.210 (CG.6210), which should come onto the market soon. They recently came out of tissue cul- ture and are being propagated by nurseries now. Auvil, who is heading the trials in Washington, said those two Soils and Weed Control GERALDINE WARNER/GOOD FRUIT GROWER Geneva 210, a more vigorous rootstock than Malling 9 or G.41, yielded just as well in untreated ground as in fumigated ground in a replant trial in Wapato, Washington. Rootstock yields Cumulative yields from Gala trees in a rootstock trial in Wapato, Washington, 2007-2013. bins per acre 100 bins per acre 200 bins per acre 300 bins per acre 400 B.9 M.9 EMLA G.16 G.222 G.11 G.41 G.210 G.890 G.935 G.214 G.30 B.9 M.9 EMLA G.41 G.222 G.16 G.935 G.214 G.210 G.30 UNFUMIGATED SOURCE: TOM AUVIL, WASHINGTON TREE FRUIT RESEARCH COMMISSION 2007 2008 2009 2010 2011 2012 2013 Color key 30-35% size of seedling G.11 G.41 Geneva rootstocks by tree size Mark B.9 M.9 (small) T337 M.9 (large) Pajam 2, EMLA Nic29 M.26 M.7 MM106 B.118 Seedling 15-30% size of seedling 35-40% size of seedling G.16 G.210 G.214 G.222 G.935 40-50% size of seedling G.30 G.202 G.890 G.969 50-75% size of seedling Over 75% size of seedling (Modified for Washington State conditions by Terence Robinson at Cornell University and Gennaro Fazio, USDA, Geneva, New York.) Fire blight resistant: G.11, G.16, G.202, G.222, G.969 Replant tolerant: G.30, G.41, G.210, G.214, G.890, G.935 Wooly apple aphid resistant: G.41, G.210, G.214, G.890 SOURCE: WASHINGTON TREE FRUIT RESEARCH COMMISSION/GENNARO FAZIO, USDA Rootstocks UNDER TRIAL