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Benjamin D. Toft, Mobashwer M. Alam, John D. Wilkie, and Bruce L. Topp

on light interception ( Loreti et al., 1976 ; Robinson, 1996 ). For temperate crops such as apple, the use of pruning, detailed training, and rootstocks to control tree size has allowed a reduction in tree spacing and has led to increased flowering

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Anke van der Ploeg, Susana M.P. Carvalho, and Ep Heuvelink

converted into dry mass [i.e., light use efficiency (LUE)] and/or by increasing light interception due to a higher leaf area index (LAI). Thus far, little is known about the mechanisms responsible for increasing plant biomass at suboptimal temperatures

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Liang Zheng, Qi Zhang, Kexin Zheng, Shumei Zhao, Pingzhi Wang, Jieyu Cheng, Xuesong Zhang, and Xiaowen Chen

; Fan et al., 2016 ; Sun et al., 2016). Diffuse light plastic film enhanced the uniformity of light distribution within the tomato canopy and increased the PPFD in the middle and lower canopies. Because of the increased light interception in the middle

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Lisa McFadyen, David Robertson, Margaret Sedgley, Paul Kristiansen, and Trevor Olesen

years for the least precocious. Once in production, yields tend to increase with increasing tree size, up to very high levels of orchard light interception [≈94% ( McFadyen et al., 2004 )]. At even higher levels of light interception, there is some

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Luca Corelli-Grappadelli, Gianfranco Ravaglia, and Eugenio Magnanini

Training system efficiency may be defined as the ratio of fruit produced to the amount of light intercepted by the canopy. In apple, a positive, linear relationship between yield and light intercepted is generally found, but in peach similar data are hard to come by. This paper reports data from an ongoing training systems trial now in the 7th year, with trees trained as Y, palmette, and delayed vase. During the life of the orchard, light interception has been measured for the different tree shapes, the yields have been recorded, and, in some years, whole-canopy gas exchanges of cropping trees have been measured. In general, the trees have been intercepting light in amounts proportional to canopy shape and tree density, with the Y (planted at higher density) intercepting more light than the other two systems, which appear more comparable to each other, despite the fact that they intercept light during the day in different ways, with the delayed vase exposing more or less the same leaves to incoming light during most of the day. Cropping has followed the amounts of light intercepted, with higher yields for the Y, without appreciable differences in fruit quality traits. The data accumulated so far indicate furthermore that the palmette and the delayed vase, despite slightly different light interception potentials (lower for the palmette), have similar yields. This might depend in part on the fact that these two systems intercept light according to different patterns during the day, with the palmette—which distributes the light intercepted in a more even fashion between the two sides—perhaps at an advantage over the vase in terms of managing the stress of excessive light (heat) loads during the central hours of the day. Whole canopy Carbon exchange data have been found to be in agreement with the patterns of light interception.

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Leonardo Lombardini, Hermann Restrepo-Diaz, and Astrid Volder

. Orchard crops, such as pecan, typically intercept 65% to 70% of the available sunlight ( Wood, 1996 ) with up to 95% light interception in overcrowded, unpruned orchards ( Lombardini, 2006 ). Orchard profitability depends on efficient absorption and use of

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Claudia Elkins and Marc W. van Iersel

2 after 10 d, which represented ≈1% of the surface area of the tray ( Elkins, 2020 ). Plants this small may benefit from larger leaves to increase light interception and presumably canopy photosynthesis and growth. This has the potential to shorten

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Terence L. Robinson

`Empire'/M.26 apple trees which were planted in 1978 and trained to a Y-trellis were pruned differentially from 1989-1993. Trees were dormant pruned by removing from 1-4 scaffold limbs. The annual increase in trunk cross-sectional area (TCA), and the number and length of shoots removed during summer pruning increased linearly as the severity of pruning increased. The number of shoots removed during summer pruning from the most severe pruning treatment was more than double that of the least severe treatment Cumulative fruit number and yield were reduced linearly with increasing severity of pruning while average fruit size was increased only slightly by severity of pruning. Light interception was reduced with increasing severity of pruning. Tree efficiency of converting light energy into fruit (g fruit/MJ PAR intercepted) was linearly reduced with increasing pruning severity. Most of the reduction in conversion efficiency appeared to be due to reduced partitioning of resources into fruit since partitioning index (g fruit/unit increase in TCA) was more highly correlated to pruning severity than to conversion efficiency. Conversion efficiency and partitioning index accounted for a greater portion of the yield variation than did light interception indicating that the influence of pruning on yield was more a function of changing internal physiology than reduced light interception.

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Frank Kappel and Rob Brownlee

To determine how different training systems affected early growth and fruiting (first 5 years), `Conference' pear (Pyrus communis L.) trees on Quince A (Cydonia oblonga L.) rootstock were trained to angled trellis, slender spindle, vertical axe, or Y-trellis. The trees of the Y-trellis had the greatest spread after 5 years, and the vertical axe and slender spindle trees were the tallest. The Y-trellis trees had the highest light interception and had significantly higher yields in 1997 than the other training systems. Average fruit weight was inversely related to crop load.

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Shumin Li, Nihal C. Rajapakse, and Ryu Oi

Growth chamber experiments were conducted to investigate the effectiveness of several photoselective plastic films in controlling height of `Sweet Success' cucumber, `Mt. Pride' tomato, and `Capistrano' bell pepper transplants. Four types of treatment films; a control, two far-red light intercepting films (YXE-1 and YXE-10), and a red light intercepting film (SXE-1), with R: FR ratios of 1.0, 2.0, 1.6, and 0.8, respectively, were used as the covering materials of experimental chambers. Photosynthetic photon flux (PPF) was adjusted to be the same in all chambers with cheese cloth. Treatment period for cucumber and tomato was 15 days and that for bell pepper was 20 days. At the end of the treatment, significantly shorter plants were found in both YXE-1 and YXE-10 chambers for all the three tested crops. However, YXE-10 was more effective than YXE-1 in producing compact cucumber, tomato and bell pepper transplants. SXE-4 film produced taller plants than control film. Magnitude of response to filtered light varied with the crop species. Number of leaves was not significantly affected by the light transmitted through photoselective filters, indicating that the height reduction was mainly caused by the reduction in internode length. With the commercial development of photoselective greenhouse covers or shade material in the near future, nursery and greenhouse industry could potentially reduce the cost for growth regulating chemicals, reduce the health risks to their workers and consumers, and reduce environmental pollution.