2007 Annual Report 1a.Objectives (from AD-416) Investigate the resistance or tolerance of Geneva apple rootstocks to apple replant disease at several grower sites in Washington State, and evaluate the genetic interactions between apple rootstocks and beneficial flourescent pseudomonads as an alternative to soil fumigants. 1b.Approach (from AD-416) Maintain at least 6 field trials over a period of four years. One major requirement is that the trials fit into a commercial setting (i.e. large enough to be managed by growers and of economical value to growers). The establishment of such trials will depend on the availability of rootstock liners in large enough quantities to be tested. There are three phases within this objective:1) propagation of rootstocks and tree design,. 2)Establishment of trials, and. 3)Data collection at the sites (data will include yearly trunk cross sectional area, yield, growth characteristics, microbial counts, etc.). These trials will be established in locations with a documented history of replant disease. We will compare performance between rootstocks planted in fumigated vs. non-fumigated soils. We will test several advanced selections from the Geneva breeding program for genetic interaction with replant disease components. Initially, our program in Geneva will ship liners to be tested in Dr. Mazzola's lab (Wenatchee, WA) and during the process we will acquire expertise to perform such experiment in-house. If significant differences are found among advanced selections, we will test half sib populations and study the inheritance of such interactions. 3.Progress Report SIGNIFICANT FINDINGS AND DEVELOPMENTS:(1) a graft in place replant experiment with the widest selection of Geneva rootstocks ever tested in WA has been planted in Vantage, WA and a new replant experiment with a wider selection of Geneva rootstocks has been planted in Brewster, WA.(2) With regards to tree deaths due to fire blight and other causes in the Wapato replant trial rootstock M.9 Pajam 2 came in first with 25 trees and Supporter 1 and 2 with 15 trees each. Geneva 41 and Supporter 3 only suffered 2 tree deaths each. We can still detect an effect on tree growth from the fumigation treatment and we can also detect rootstocks that show tolerance to the replant components in Wapato. The rootstock PI AU 56-83 had to be removed from the experiment because it was unproductive and large.(3) The rootstock B.9 has been one of the weakest and least productive rootstocks in the replant experiments that have been planted so far. G.41 has performed well in the replant settings of Wapato (conventional) and Chelan (organic).. 4)The positive effect on season’s tree growth of fumigation treatment has virtually disappeared in the third season while the cumulative effect is still detectable. OBJECTIVE 1. There are three phases within this objective:1) propagation of rootstocks and tree design,2) Establishment of replant trials, and. 3)Data collection at the sites and analysis. At the onset of this period we had already established 3 Apple Replant Disease (ARD) and two non ARD field trials. In the spring of 2006 we established three additional ARD field trials (Wapato, Vantage and Brewster) the Vantage field trial is unique because even though it has been placed in a fumigated replant setting, it utilized grafted liners instead of finished trees thus fitting elements of proposed Objective 2. The new Wapato trial is part of the NC-140 replant trials being established in the U.S. All trials have generally fit the major requirement that the trials be placed into a commercial setting (i.e. large enough to be managed by growers and of economical value to growers). The establishment more of such trials will depend on the availability of rootstock liners in large enough quantities to be tested. OBJECTIVE 2 Many growers are purchasing rootstock liners and contracting nurseries to make sleeping eyes (SE) or bench grafts (BG)instead of planting finished trees. This year we planted a bench graft experiment in a fumigated replant trial location at the Auvil Fruit Tree Farm (Vantage, WA) the planting in Vantage is on a V trellis and has the widest array of Geneva rootstocks planted in WA. Bench grafts are allowed to push growth for two season to build a scaffold that closely matches the wires in the trellis. Trees are expected to reach optimum height prior to fruiting. Data on central leader growth and number of trained branches has been taken this year. A few rootstock genotypes (G.16, 4002, 4019) showed latent virus susceptibility and have been eliminated from the trial. Liner quality (roots) may have had a strong effect on graft and tree establishment on a few select rootstocks. It was not a major factor for success given the TLC that the grower gave the the trial.