CROP LOAD AND FRUIT QUALITY OF 'FORTUNE' PLUM

The long pruning technique with plum trees allows for high fruit yields but requires attentive regulation of crop loads. The objective of the present work was to identify the crop load that allows for high yields without a decline in fruit quality. The experiment was conducted on ‘Fortune’ plum grafted on ‘Myrabolan 29C’ rootstock. The orchard tree density was 1000 trees/ha, with trees trained to a “free palmette” with long pruning (no heading of retained shoots). The experimental design had 8 randomized blocks with 1 tree per replication. Fruit thinning levels ranged from 80 to 180 fruits per tree in the third year, 120 to 220 fruits in the fourth year and from about 300 up to 680 fruits in the fifth year. Vegetative, reproductive and fruit quality parameters were measured annually. The results confirmed the negative relationship between tree crop load and fruit weight, but the response was not linear. Therefore, it was possible to identify, according to tree age, the crop load intervals within which it is possible to predict fruit weight and quality. In the 5th year, at full tree maturity, with a yield of 40 t/ha the mean fruit weight was 120 g and fruit soluble solids contents around 12 °Brix. With 65 t/ha, the mean fruit weight was reduced to ~95 g and fruit soluble solids content to 11 °Brix. The absence of fruit thinning generated a decline of qualitative fruit traits.