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- Author or Editor: Steven S. Denning x
Manipulating radiation interception by using horizontal and vertical trellis forms was tested for effects on water loss and photosynthesis on sunny days. Water loss from 15 potted Pinot Noir vines of each form was estimated by weighing the vines at two hour intervals during the day. Radiation interception for vines and gas exchange of individual exposed leaves was measured over the day to evaluate the leaf activity patterns in relation to exposure patterns. Similarly, diurnal whole vine photosynthesis measurements were taken by using clear plastic “balloon” whole vine chambers. The horizontal form had higher radiation interception than the vertical form during the day, resulting in higher water loss from the horizontal form. Under N-S orientation, the horizontal form showed a gradual decrease in exposed leaf and whole vine photosynthesis starting in late-morning while the vertical form had a more uniform pattern over the day. The long periods of leaf exposure of horizontal canopies appears to induce a photosynthetic decline that also reduces afternoon transpiration. Vertical forms have two populations of leaves that are exposed for shorter periods, thus less photosynthetic decline occurs. Vertical trellis forms may have potential for improving water use efficiencies in arid regions with high radiation.
A 14-year-old trial of `Empire' apple production systems (Slender Spindle/M9, Central Leaders on M7 and 9/111 interstems, and Y-trellis/M26) had shown significant yield differences that were primarily related to total light interception, but yield of fruit/MJ light interception, however, was still higher in the Y-trellis. The hypothesis tested was that in healthy orchards yields are related primarily tototal light intercepted by the spur canopy. In 1991 seasonal leaf area development, exposed leaf photosynthesis, fruit growth, total light interception (by image analysis of fisheye photos) and relative light interception by different shoot types (by a laser sunbeam simulator) were estimated. The results reflected the mature, spurry nature of these trees. The final LAI values were CL/7=1.8, CL/9/111=2.3, SS/9=2.6 and Y/26=3.6. Exposed leaf photosynthesis showed few differences. Yields of the pyramid forms were 40-42 t/ha while Y-trellis gave 59 t/ha, with similar fruit sizes. Again, yields were primarily related to % total light interception (48-53% for pyramid forms versus 62% for the Y). Laser analyses showed that the Y intercepted more light with the spur canopy than the pyramid forms, supporting the hypothesis. Yields were better correlated with spur canopy LAI and spur canopy light interception than with shoot canopy LAI and light interception.
Although apple (Malus domestica Borkh.) system yield differences are generally related to whole-canopy light interception, this study tested the hypothesis that these orchard yields are related primarily to total light intercepted by the spur canopy. Seasonal leaf area development of different shoot types, exposed bourse shoot leaf net photosynthesis, fruit growth, whole canopy light interception (by image analysis of fisheye photographs) and relative light interception by different shoot types (by a laser assisted canopy scanning device) were estimated within four 14-year-old `Empire' apple production systems (slender spindle/M.9, central leader/M.7, central leader/M.9/MM.111 and Y-trellis/M.26). The final LAI values were CL/M.7 = 1.8, CL/9/111 = 2.3, SS/M.9 = 2.6 and Y/M.26 = 3.6. Exposed leaf net photosynthesis showed few differences and was not dependent upon the production system. Yields of the pyramidal shaped tree forms were 40 to 42 t·ha-1 while Y-trellis produced 59 t·ha-1, with similar fruit sizes. Again, yields were primarily related to the percentage of light intercepted by the whole canopy, 48% to 53% for conic forms versus 62% for the Y-trellis system. Laser analyses showed that the Y-trellis system intercepted about 20% to 30% more light with the spur canopy than the conic tree forms, supporting the hypothesis. Yields were better correlated with spur canopy LAI and spur canopy light interception than with extension shoot canopy LAI and light interception.
The objectives of this study were to: (1) compare four methods of estimating daily light interception (fisheye photography with image analysis, multiple light sensors, ceptometer and point grid) with various apple tree forms (Slender Spindle, Y- and T-trellises and vertical Palmette) and (2) evaluate the interaction of tree form, time of day and atmospheric conditions on light interception. All methods were highly correlated to each other (R2≥92%) for estimated daily mean % total light interception by the various tree forms. Fisheye photography, ceptometer and sensor generated almost equal daily mean values of intercepted light by each tree form, whereas by using point grid values were slightly lower. Interactions of tree form, time of the day and diffuse/direct radiation on estimated light interception were found. Under overcast skies, daily variations in total light interception were small for all tree forms. Under clear skies, the time-of-day effect on light interception strongly increased from horizontal to vertical tree canopies, indicating the importance of multiple readings in upright canopies. All methods had advantages and disadvantages, but the good results obtained by using the rapid, inexpensive point grid method (counting of shaded points on sheet under canopy) on clear days may allow estimates of orchard light interception when other methods are too costly and/or time-consuming.
This study examined the hypothesis that late-season European Red Mite (ERM) injury effects on fruit development are mediated via carbon relations of apple trees. ERM injury were allowed to develop in mature semi-dwarf `Starkrimson Delicious'/M26 trees with moderate crops (about 30 t/ha). Populations of ERM developed concurrently in all trees, but were controlled with miticides at different mite-day levels, giving a range of final mite-days from 300 to 2100 on individual trees as estimated by weekly leaf sampling for mites. At intervals through the season fruit growth was monitored. Diurnal whole tree photosynthesis was measured with eight clear flexible “balloon” whole tree chambers. Before the mite injury developed, fruit sizes were very similar, but in the last 60 days before harvest differences in fruit weights of up to about 50 grams were induced by mite injury which reduced whole tree photosynthesis comparably. The final fruit growth and size were well correlated with whole tree photosynthesis per fruit. Effects on other fruit quality factors were minor. These results suupport the hypothesis that whole tree source/sink balance may be an integrator of crop load and mite injury effects on fruit development. Fruit growth rates may be a practical monitor of the integrated effects of crop load and stresses.