Studies on Yield Efficiency of Fruiting Units in 'Fuji' Apple Trees

Abstract

The influences of shoot growth, composition of 1-and 2-year-old branches, and fruit set on yield efficiency of fruiting branches in 'Fuji' apple trees/Marubakaido (Malus prunifolia Borkh. var. ringo Asami), trained to an open-center shape, were investigated. The efficiency of fruiting branches expressed as the number of fruits per unit of total leaf area (FLA, Fruits/m²)(per branch) varied from 0.7 to 13.3 with an average value of 5.0 for all branches. Age, orientation, elevation above the ground, and vigor of fruiting branches did not account for a large portion of the variations in the efficiency of fruiting branches. A strong inverse relationship exists between Log₁₀ FLA and bud production rate (BPR)(shoot count per 1-yr-old branch). BPR is positively correlated to leaf area per 1-yr-old branch (r≥0.807). Leaf area per 1-yr-old branch decreased with ; 1) increasing proportions of terminal spur on 1-and 2-yr-old branches and 2) decreasing long axillary on 1-and 2-yr-old branches. Leaf area per 1-yr-old branch increased rapidly below 30 % of the short terminal on 1-yr-old branch (terminal spurs). The regression equations for Log₁₀ FLA on BPR differed significantly among trees but not in the slopes. Tree with the highest FLA across all BPR had the highest fruit set.