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Jens N. Wünsche and Alan N. Lakso

The study evaluated the relationship of spur vs. extension shoot leaf area and light interception to apple (Malus {XtimesX} domesticaBorkh.) orchard productivity. Fifteen-year-old `Marshall McIntosh'/M.9 trees had significantly greater leaf area and percentage of light interception at 3-5 and 10-12 weeks after full bloom (AFB) than did 4-year-old `Jonagold'/Mark trees. Despite significant increases in leaf area and light interception with canopy development, linear relationships between total, spur, and extension shoot canopy leaf area index (LAI) and 1) light interception and 2) fruit yield were similar at both times. Mean total and spur canopy LAI and light interception were significantly and positively correlated with fruit yield; however, extension shoot LAI and light interception were poorly correlated with yield. In another study total, spur and extension shoot canopy light interception varied widely in five apple production systems: 15-year-old central leader `Redchief Delicious' MM.111, 15-year-old central leader `Redchief Delicious' MM.111/M.9, 16-year-old slender spindle `Marshall McIntosh' M.9, 14-year-old `Jerseymac' M.9 on 4-wire trellis, and 17-year-old slender spindle `MacSpur' M.9. Yields in these orchards were curvilinearly related to total and extension shoot canopy light interception and decreased when total light interception exceeded 60% and extension shoot interception exceeded 25%. Fruit yields were linearly and highly correlated (r 2 = 0.78) with spur light interception. The findings support the hypothesis that fruit yields of healthy apple orchards are better correlated with LAI and light interception by spurs than by extension shoots. The results emphasize the importance of open, well-illuminated, spur-rich tree canopies for high productivity.

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Waldemar Treder and Augustyn Mika

`Lobo' apple (Malus {XtimesX} domestica) trees grafted on Malling 26 (M.26) were planted on flat ground or on raised beds covered with black polyethylene. In both planting systems trees were drip irrigated to maintain soil water potential within the range of 0 to -0.02 MPa (0 to -0.3 lb/inch2) or were left without irrigation. Planting methods and irrigation influenced tree growth. Standard planted trees and irrigated trees grew stronger, whereas planted on beds less vigorously, irrespective to irrigation. The yield of all trees increased with time until the fourth year of production. Fruit size decreased as yield increased. Also lack of irrigation considerably reduced average fruit weight. Yield and trunk cross-sectional area (TCA) measurements were used to calculate crop density coefficient (CD). CD values varied considerably between the treatments showing their dependence on planting method, irrigation and tree age. In most cases, the correlation coefficient between CD and average fruit weight were negative, indicatingthat the weight of individual fruit decreased with increasing numbers of fruit per unit of TCA. We question whether CD coefficient may be universally used under wide range of environmental conditions and cultural practices.