‘Elberta’ (Prunus persica (L.) Batsch) peach seedlings were grown in nutrient solutions for 27 days with aluminum concentrations of 0, 222, 666 and 2000 μm; the 2000 μm concentration induced A1 toxicity symptoms in leaves and severely restricted root growth. The early stage of A1 toxicity was characterized by marginal chlorosis that later developed into necrotic areas that extended along the veins toward the midrib. Advanced stages of toxicity were characterized by collapse of the midrib, terminal dieback and defoliation of the seedlings which are typical symptoms of calcium deficiency in peaches. At high A1 concentrations roots died back and new roots developed as irregularly shaped cylinders with constrictions and enlargements at the root apex.

Studies were conducted on peach [Prunus persica (L.) Batsch] during 1988 to 1990 to test the performance of a tree-width rope-curtain bloom thinner and a rotating rope-curtain thinner. Six trips over the tree canopy were required with the tree-width rope curtain, and only one trip was required with the rotating curtain to thin to a spacing of about one flower per 9 cm of fruiting shoot length. Based on the number of flowers per square centimeter of branch cross-sectional area (CSA) immediately following thinning and the number of fruit per square centimeter of CSA following June drop, rope-curtain thinning was equal to hand-thinning at full bloom (FB). Rope-curtain thinning reduced hand-thinning time by 40% and increased harvest fruit weight by 10% to 20%. Research on various modifications in tree training/pruning indicated that performance of the mechanical thinner was negatively correlated with shoot density. Thinning was maximum on open-center-trained trees on which detailed pruning had been conducted to eliminate overlapping shoots.

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Variability in maturity within a peach (Prunus persica, L. Batsch) fruit was estimated by measurements of force and the soluble solids concentration (SSC) at 16 coordinates around the peach at five maturity stages: 1) about one-half final swell (immature); 2) 85% final swell (green); 3) firm-ripe and similar to chip #3 of the Clemson Univ. system; 4) firm-ripe and similar to chip #5; and 5) tree-ripe. Firm-ripe 3 and 4 stages were firm enough to ship, but the tree-ripe stage was too soft. Firmness measured with a 4.7-mm-diameter penetrometer tip from two cultivars indicates a strong trend for the peach tip and cheeks to be firmer than tissue at other coordinates. Coordinates at the equator and around the stem end are generally firmer than coordinates at lat. 45°N, particularly in stages 3, 4, and 5. The SSC in juice from a cylinder of fruit adjacent to the puncture was higher at long. 90°E-W than at the sutures and higher at lat. 0° than at 70°S. Variance increased for force and decreased for SSC between maturity stages to the firm-ripe stage. The coordinate technique might be used to characterize and select cultivars that would be most suitable for once-over harvests.