Orchard comparisons of `Cox's Orange Pippin' grown on selections of the apple rootstock M.9

Abstract

SummaryTwenty four selections (clones) of M.9 were compared as rootstocks for the apple cv. Cox's Orange Pippin in three orchard trials planted on similar sites at Horticulture Research International (HRI)-East Malling between 1980 and 1987. Rootstock clone effects on maiden tree quality were inconsistent in two of the trials, and appeared to be associated more with nursery conditions at the time of raising the trees than with the clone of rootstock used. Shoot growth following planting in the orchard was related positively to tree size (maiden tree height and feathering) at the time of planting and no differences in initial tree vigour were attributable to rootstock clone. Tree size differences at maturity were variable between trials, were small (10% to 30%), and in most instances not statistically significant. Nevertheless, the scion weights of trees on the Dutch T.337, the French INRA 71/0 and Lancep (Pajam 1) rootstock clones were 10% to 30% smaller than trees on the EMLA clone when the trials were terminated. None of the clones had any consistent effect on the precocity of flowering, the numbers of floral buds produced by the trees, or the efficiency of fruit set. In two of the three trials, annual yields and cumulative yields per tree were very similar for trees on all the M.9 clones, even when adjusted for differences in tree size at planting. Estimates of yield efficiency in each year (yield in kg cm22 trunk cross sectional area) also showed no statistically significant differences between any of the M.9 clones in these two trials. In a third trial, yield precocity in the first three cropping years was much lower than average for trees on the Belgian clone Nic.29, the French clone INRA 71/0 and the German clone SP.1 (719), even after adjustments to take account of differences in tree size at planting. Trees on the Dutch selection T.340, the Belgian selections Nic.16 and Nic.19 the German selection SP.18 (751) and M.9A also showed reduced yield efficiency compared with trees on the EMLA clone in two of these three years. No differences were recorded in the mean fruit size at harvest or the yield of fruits in the highest quality grades in this third trial.