Effect of Dwarf Apple Rootstocks on Average ‘Gala’ Fruit Weight at Six Locations Over Three Seasons

Abstract

The influence of rootstock on average fruit weight of ‘Gala’ apple [ Malus× sylvestris(L) var. domestica(Borkh.) Mansf] was evaluated for a subset of data from the 1994 multi-location NC-140 apple rootstock trial. Data for 10 dwarfing rootstocks (M.9 EMLA, M.26 EMLA, M.9 RN29, M.9 Pajam1, M.9 Pajam2, B.9, O.3, V.1, Mark, and M.9 NAKBT337) at six locations for three years were used. Analysis of covariance was used to evaluate the effect of rootstock on average fruit weight when crop density was included in the linear model as a covariate. For five of the 18 data sets, rootstock variances were not equal, so a heterogeneous variance model was used. Rootstock significantly affected average fruit weight in 16 of the 18 data sets, but the rootstock by crop density interaction was significant for only one data set. Trees on M.9RN29 (also known as M.9Nic29), B.9, and M.9T337 (usually referred to as M.9NAKBT337) tended to produce the largest fruit and trees on Mark tended to produce the smallest fruit. Although rootstock significantly influenced average fruit weight at 16 of the 18 location-year combinations, results were not very consistent from one location to another or from year to year within a location. Possible explanations for these unexpected results are discussed.