EFFECT OF CROP LOAD ON FRUITING AND LEAF PHOTOSYNTHESIS OF BRAEBURN M.26 APPLE-TREES/

Four-year-old apple (Malus x domestica Borkh.) trees cv. 'Braebum' on M.26 rootstock were thinned at full bloom to establish six crop loads ranging from a heavy crop to a deflowered treatment. At harvest, mean yield per tree varied from 0 to 38 kg and mean fruit weight ranged fro m 225 g in the heaviest cropping treatment to 385 g in the lightest cr opping treatment. Light cropping resulted in a significant advance in fruit maturity as indicated by background color, starch/iodine score a nd soluble solids. There were small differences in leaf photosynthetic rate among the treatments when shoot growth was active. However, in e arly January, coincident with cessation of shoot growth and maximum ra te of accumulation of fruit weight, leaf assimilation rate was reduced by as much as 65% on the deflowered trees compared to the trees carry ing the heaviest crop. Leaf assimilation rate showed a curvilinear res ponse to crop load at this time, with little increase in leaf assimila tion when crop load exceeded 12 fruit m(-2) leaf area.