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Ido Schechter, D.C. Elfving, and J.T.A. Proctor

Mature apple (Malus domestic a Borkh.) trees with “Starkspur Supreme Delicious” as the scion grafted on nine different rootstocks were studied in 1987 and 1988. Canopy seasonal development and its light interception were examined using fisheye (hemispherical) photographs Rootstock affected the amount of structural wood, the rate of canopy development and the final leaf area. However, rootstock did not affect the sigmoidal pattern of canopy development. Photosynthesis (Pn) was measured under field conditions. Shoot leaves, spur leaves on spurs without fruits (S-F), and spur leaves on spurs with fruit (S+F) from trees on M.26 EMLA and OAR 1 showed no differences in Pn rates. However, for both rootstock, shoot leaves had the highest Pn rate, S+F the lowest, and S-F leaves had intermediate values Growth and yield components were assessed by leaf separation into shoot and spur leaves while harvesting them. Rootstock strongly affected the canopy leaf distribution as well as leaf number, dry weight, area, number of spurs and yield PCLC. Yield efficiency was mainly dependent upon spur leaf dry weight. OAR 1 performed uniquely in this study

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Y.L. Grossman and T.M. DeJong

Plant dry matter production is proportional to light interception, but fruit production does not always increase with increased light interception. Vegetative growth potential, the effect of cropping on vegetative growth, light interception and cropping efficiency of a clingstone peach [Prunus persica (L.) Batsch `Ross' on `Nemaguard' rootstock] were assessed in four production systems differing in tree density and training system. The four systems were a perpendicular V (KAC-V) system, a high-density perpendicular V (HiD KAC-V) system, a cordon system, and an open vase system. Vegetative growth potential, assessed on defruited trees, was higher in the cordon system and lower in the open vase system compared to the V systems. Cropping reduced leaf growth on the V and cordon systems and stem growth on the KAC-V and cordon systems. On a ground area basis, the HiD KAC-V system had the highest crop yields and the open vase system had the lowest. The cordon and HiD KAC-V systems intercepted more light and produced more fruit, stem, and leaf biomass than the open vase system. However, the modified harvest increment, the ratio of fruit dry mass to the sum of fruit, leaf, and stem dry mass, was lower in the cordon system than in the other systems. Thus, on this basis, the cordon system was the least efficient. On a trunk cross-sectional area basis, there were no significant differences in fruit production among any of the four training systems. For current year production, crop production per unit ground area is the best measure of economic efficiency. However, when planning the spacing, training and pruning of orchard trees, the most appropriate goal seems to be a system that increases light interception without increasing vegetative growth potential, such as the HiD KAC-V system.

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Terence L. Robinson

In 1986, an orchard systems trial was planted with `Empire' and `Jonagold' on M.26 rootstock to compare the performance of the Y-trellis training system at a range of spacings and rectangularities. There were four in-row spacings ranging from 90 cm to 3.66 m and four between-row spacings ranging from 3 to 6 m, giving tree densities from 472 trees/ha up to 3588 trees/acre. Rectangularities ranged from 0.83 to 6.67. In several cases, different spacings gave the same tree density, but with different rectangularity. Trees were trained to a Y-shaped trellis with a 60° angle. Scaffold branches were trained to the wires on each side of the Y in a fan-shaped arrangement. At the closest in-row spacing only two scaffolds were allowed per tree, while at the widest in-row spacing up to 12 scaffolds were allowed per tree. At the end of 11 years, tree weight and cumulative yield per tree were negatively correlated to tree density, while light interception and cumulative yield per hectare were positively correlated to tree density. However, the relationship was weakened by differing results with different rectangularities at the same spacing. As rectangularity increased at a given density, tree size, yield, and light interception were reduced. However, at the lower densities, trees failed to completely fill the trellis when rectangularity was low, thus limiting yield per hectare. Fruit red color was reduced at the highest densities and increased with increasing rectangularity.

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Cheryl R. Hampson, Harvey A. Quamme, Frank Kappel, and Robert T. Brownlee

The effect of increasing planting density at constant rectangularity on the vegetative growth and light interception of apple [Malus ×sylvestris (L) var. domestica (Borkh.) Mansf.] trees in three training systems (slender spindle, tall spindle, and Geneva Y trellis) was assessed for 10 years. Five tree densities (from 1125 to 3226 trees/ha) and two cultivars (Royal Gala and Summerland McIntosh) were tested in a fully guarded split-split plot design. Planting density was the most influential factor. As tree density increased, tree size decreased, and leaf area index and light interception increased. A planting density between 1800 and 2200 trees/ha (depending on training system) was needed to achieve at least 50% light interception under the conditions of this trial. Training system altered tree height and canopy diameter, but not total scion weight. Training system began to influence light interception in the sixth leaf, when the Y trellis system intercepted more light than either spindle form. Trees trained to the Y trellis tended to have more spurs and a lower proportion of total leaf area in shoot leaves than the other two systems. The slender and tall spindles were similar in most aspects of performance. Tall spindles did not intercept more light than slender spindles. `Royal Gala' and `Summerland McIntosh' trees intercepted about the same amount of light. `Royal Gala' had greater spur leaf area per tree than `Summerland McIntosh', but the cultivars were similar in shoot leaf area per tree and spur density.

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R. Scott Johnson and Alan N. Lakso

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Haijie Dou, Genhua Niu, and Mengmeng Gu

). Theoretically, quantum yield of a dense plant canopy should be more equalized under green light as a result of increased light interception by lower leaves, which could potentially increase whole-canopy photosynthesis and, subsequently, increase plant yield. In

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Bruce H. Barritt, Curt R. Rom, Bonnie J. Konishi, and Marc A. Dilley

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Byron Taylor Whisnant and Leonardo Lombardini

Pecan tree pruning is a standard cultural practice in commercial pecan farming operations. Pruning often promotes canopy light infiltration, air movement, and crop load management. Timing of pecan tree pruning is often during winter for labor and time management purposes, yet the most effective pruning time is not known for pecan. `Pawnee' trees were pruned during March (winter), May, June, July and August in a commercial orchard in Charlie, Texas during the 2003 and 2004 growing seasons. June pruning produced the greatest two year summed annual average yield (2447.7 kernel lb/acre), largest increase of kernel lb/acre (625%) and largest increase percent kernel (113%) between 2003 and 2004. Furthermore, June produced the largest nuts (39.8 nuts/lb) with the lowest yield (337.5 kernel lbs/acre) in 2003, and smallest nuts (59.4 nuts/lb) with the highest yield (2110.2 kernel lb/acre) in 2004. March pruning produced the least variable yield of kernel lb/acre (38% decrease) between 2003 and 2004. July pruning produced the most consistent percent kernel (1.3% increase) between 2003 and 2004. August pruning produced the lowest two year summed annual average yield (879.8 kernel lbs/acre). Percent light transmission and leaf area index data showed no correlation with pruning times and kernel yields. Data collection will continue for another 2 to 3 years to asses the continuous affects of varied pruning times.

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William L. Bauerle and Joseph D. Bowden

This report describes a system for integrating photosynthetically active radiation (PAR) using fiberoptics. Many photoelectric sensors or 1-m-long line sensors that integrate individual interception points for spatial averaging were replaced with fiberoptics, which integrate interception points. Depending on the positioning of optical fibers and the amount of fibers terminated at a PAR sensor, whole-plant, canopy layer, and individual leaf light interception can be determined. The use of fiberoptics has the added advantage of being very small in comparison to the bulk of a typical quantum sensor. The fiberoptic-based system potentially is a more accurate, less expensive method to integrate PAR throughout plant canopies than PAR sensors.

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Terence L. Robinson and Alan N. Lakso

Bases of orchard productivity were evaluated in four 10-year-old apple orchard systems (`Empire' and `Redchief Delicious' Malus domestics Borkh. on slender spindle/M.9, Y-trellis/M.26, central leader/M.9/MM.111, and central leader/M.7a). Trunk cross-sectional areas (TCA), canopy dimension and volume, and light interception were measured. Canopy dimension and canopy volume were found to be relatively poor estimators of orchard light interception or yield, especially for the restricted canopy of the Y-trellis. TCA was correlated to both percentage of photosynthetically active radiation (PAR) intercepted and yields. Total light interception during the 7th to the 10th years showed the best correlation with yields of the different systems and explained most of the yield variations among systems. Average light interception was highest with the Y-trellis/M.26 system of both cultivars and approached 70% of available PAR with `Empire'. The higher light interception of this system was the result of canopy architecture that allowed the tree canopy to grow over the tractor alleys. The central leader/M.7a had the lowest light interception with both cultivars. The efficiency of converting light energy into fruit (conversion efficiency = fruit yield/light intercepted) was significantly higher for the Y-trellis/M.26 system than for the slender spindle/M.9 or central leader/M.9/MM.111 systems. The central leader/M.7a system bad the lowest conversion efficiency. An index of partitioning was calculated as the kilograms of fruit per square centimeter increase in TCA. The slender spindle/M.9 system had significantly higher partitioning index than the Y-trellis/M.26 or central leader/M.9/MM.111. The central leader/M.7a system had the lowest partitioning index. The higher conversion efficiency of the Y/M.26 system was not due to increased partitioning to the fruit; however, the basis for the greater efficiency is unknown. The poor conversion efficiency of the central leader/M.7a was mostly due to low partitioning to the fruit. The Y-trellis/M.26 system was found to be the most efficient in both intercepting PAR and converting that energy into fruit.