2013 ASHS Annual Conference

Apple rootstocks are usually evaluated for 10 years, but there is an economic incentive to shorten the evaluation period. Data from the 2003 NC-140 Dwarf Apple Rootstock trial were used to determine the number of years required to separate rootstocks based on trunk cross-sectional area (TCA).  ‘Golden Delicious’ trees budded on 11 dwarfing rootstocks were planted at 12 locations with 2 trees on each rootstock randomized within four blocks in a generalized randomized complete-block design. Annual TCA data from each location were analyzed with a repeated measures ANOVA with SAS’s  Proc Glimmix and the slicediff option  was used to compare rootstock lsmeans within each year. Data for only 4 locations have been analyzed, but the relationship between TCA and year was linear in British Columbia and quadratic in Pennsylvania, Utah, and Wisconsin. Rootstocks were significantly different after 2 years in Utah, but 3 years were needed to separate rootstocks in the other locations. Depending on the location, the number of years to detect a difference between B.9 vs. M.26 was 3 or 4 years, 4 to 6 years for B.9 vs. T.337, 5 to 8 years for T.337 vs. M.26, 7 to 8 years for M.26 vs. Pajam2, and 6 to >10 years for  T.337 vs. Pajam2. Although other characteristics may take longer to sort out, it appears that rootstock trial require at least 8 years to separate M.26 and M.9 Pajam2 into different vigor classes.