The effects of crop load on fruit quality and mineral content were studied on apple trees (Malus domestica L. Borkh. cv. Cox’s Orange Pippin) by comparing fruit from heavily cropping trees with those from trees with naturally light crops or those which had been flower thinned. In light and thinned treatments, flower bud density was less, and fruit set greater than in heavy treatments. The heavy cropping trees had a higher proportion of fruiting spurs with only one fruit. When spurs with fruit of similar size at the end of the season were compared, those from the heavy treatment had greater primary and bourse leaf areas than did those from the other treatments. Average fruit size at harvest was greatest for the thinned treatment despite it having fruit numbers per tree similar to those of the light treatment. By seven weeks after full bloom, fruit from heavily cropping trees had higher calcium and magnesium contents, and by the end of the season, also lower potassium contents, than fruit from either light cropping treatments. Fruit from both light and thinned treatments had similar calcium contents, and higher incidences of bitter pit and internal breakdown after storage. Since there were no strong differences in fruit maturity with crop load, the negative effects of light cropping on fruit disorders is probably associated with the low calcium and high potassium contents in fruit from light cropping trees. These mineral effects may be related to the lower amount of leaf associated with light crop fruiting spurs.
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Volz et al. (1993) studied this question.