Effects of Shade on the Growth and Cropping of Apple Trees. III. Effects on Fruit Growth, Chemical Composition and Quality at Harvest and After Storage

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Abstract
Cox’s Orange Pippin apple trees on M.26 rootstock were shaded so as to receive 37, 25 or 11% of full daylight during the post-blossom growing season in either or both of 1970 and 1971, and the growth, composition and quality of their fruits at harvest and after storage compared with those from control trees. In 1972 a separate experiment using Cox on M.9 involved shading to 34 or 13% of full daylight. Shading reduced fruit size, through reductions of cell size and the number of cells per fruit, fruit colour and the degree of skin cracking and russeting. Fruits grown under shade had less dry matter and starch per unit fresh weight and lower rates of ethylene and CO2 production per unit weight at harvest, but samples harvested at different dates showed no evidence of any marked shift in the onset of the respiration climacteric. The incidence of core flush and shrivelling in storage was increased by shading during the growing season. There was no evidence that the concentrations of N, P, K, Ca or Mg differed in fruits of the same size produced under shaded or unshaded conditions, but smaller fruits had higher concentrations of Ca, N and P than did larger ones. Fruits grown on trees shaded for one year had less bitter pit, breakdown and rotting in storage than had control fruits because of their smaller size and higher Ca concentrations. Fruits from trees shaded in the previous year had more bitter pit and breakdown than would have been expected from their size, apparently as a result of adverse residual effects of shade on tree Ca status. The greater part of the direct and residual influence of exposure on bitter pit incidence could be statistically accounted for by the regression of bitter pit on fruit size and leaf Ca concentration.