Size factors in apple fruit

Eight ‘Golden Delicious’ apple trees on an experimental plot were systematically thinned to give different numbers of fruit per spur, per branch, and per tree. At harvest, fruits were weighed individually and their positions on spurs and branches noted. Trunk and branch girths were measured.Mean fruit weights were not significantly affected by the presence of several fruits on a spur, or by the degree of local crowding on branches, compared with the general mean for the whole tree. However, mean fruit weight varied between trees, depending on the number of fruits carried per unit of trunk girth of cross-sectional area.μ (mean fruit weight) = a — bN (number of fruit per unit trunk dimension)The distribution of fruit weights on each tree can be regarded as normal and on the 8 trees examined, standard deviations did not differ significantly. An equation was derived relating total crop per tree and fruit-size distribution to trunk dimensions and fruit number, both of which were variable from tree to tree, involving 2 coefficients of the mean size equation and the standard deviation of the weight distribution, which seem to be constant for the 8 trees under the prevailing conditions.Using the equations, it could be shown that although fruit thinning would increase the proportion of larger fruit in the crop, in only one case would careful thinning have increased the total weight of larger fruit.