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- Author or Editor: John A. Barden x
In 1997 and 1998, we determined the effects of defoliation on return bloom and fruit set following a light cropping year. In one study, `Braeburn' trees were hand-thinned to a crop density (CD) of 3 fruit/cm 2 trunk cross sectional area (TCSA) in late May 1997, and then either completely defoliated or half of the tree defoliated by hand on one of five dates between June and Sept. 1997. Compared to a nondefoliated control, both whole and half-tree defoliation on all dates reduced fruit count and yield efficiency (kilograms per square centimeter of TCSA) and affected fruit weight, starch, firmness, and soluble solids in 1997. In 1998, return bloom and fruit set were reduced by most 1997 defoliation treatments. Compared to other dates, defoliation on 3 July caused the greatest reduction in return bloom in both whole and half-defoliated trees. In another study, `Braeburn' trees were hand-thinned to a CD of 5 in late May 1998; complete defoliation by hand on 1, 15, or 29 July reduced return bloom and fruit set in 1999; the 1 July treatment resulted in zero return bloom. `Golden Delicious' and `York' trees were thinned to a CD of 3 in late May 1998 and were hand-defoliated on 21 July or 12 August by removing every other leaf or removing three of every four leaves over the entire tree. In 1999, return bloom and spur and lateral fruit set were reduced by all defoliation treatments. Fruit set was most reduced by the 12 Aug. treatment. Fruit set for `York' was lower than for `Golden Delicious' in all cases.
Deblossomed ‘Tribute’ strawberry (Fragaria × ananassa Duch.) plants had increased [14C]-photosynthates in untreated leaves 48 hr after treatment with 14CO2. The summed quantity of radioactivity in the untreated leaves and fruit of fruiting plants approximated that in the untreated leaves of deblossomed plants. There was no effect of deblossoming on the amount of 14C in the crown or roots. Autoradiographs showed that the majority of 14C was in the expanding leaves. Therefore, increased leaf production rates, which often result from deblossoming strawberry plants, may be attributed to an increase in photosynthates partitioned to the expanding leaves.
Leaf loss increased net photosynthesis (Pn) or delayed senescence of the remaining leaves in several plant species (2, 3, 7, 8). Strawberries are commonly defoliated during planting and after fruiting. The objective of this study was to determine the effects of partial defoliation on Pn rates and growth of the strawberry.
Researchers often apply treatments to limbs rather than to whole trees. This technique allows the application of large numbers of treatments to a limited number of trees, and also allows adequate replication when a chemical is in very limited supply. The obvious assumption is made that results from limb treatments arc representative of those to be expected using whole trees.
Data from several experiments will be discussed that raise serious doubts about the extrapolation of results from limb treatments to whole-trees. The data are from studies with terbacil applied to apple and peach as well as shade treatments to both apple and peach. Girdling studies will also be discussed in which branches isolated by girdling responded very differently than ungirdled branches.
Three-year-old `Campbell Redchief Delicious'/MM.111 [Malus domestica (Borkh.)] trees were subjected to a factorial arrangement of annual pruning treatments (removal of excess scaffold limbs vs. no removal, heading the terminal extension shoot on scaffold limbs vs. no heading) plus a treatment involving gradual removal of excess scaffold limbs. Six years after treatments were initiated, pruning treatment did not influence tree height or trunk size. Tree spread was greatest for nonheaded trees. Although yield, yield efficiency, and gross returns were reduced by either type of pruning, there was significant interaction between limb removal and heading. Compared to no limb removal or heading, limb removal plus heading reduced cumulative gross returns by ≈ $12,800/ha.
Net photosynthesis (Pn), transpiration (Tr), and stomatal conductance for CO2 (gs) were determined at 26° ± 1°C for leaves on intact and excised apple shoots at different vapor pressure gradients (VPG’s). Pn, Tr, and gs of leaves on intact and excised shoots responded similarly to changes in VPG. Pn and gs were not affected directly by VPG. Tr increased as VPG increased since stomatal closure did not counterbalance the increased VPG.
The influence of rootstock on average fruit weight was evaluated for a subset of data from a multilocation NC-140 apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] rootstock trial. Data for eight dwarf rootstocks were collected at four locations for 2 years. Analysis of covariance was used to evaluate the effect of rootstock on average fruit weight when crop density or number of fruit per tree was included in the linear model as a covariate. When number of fruit harvested per tree was used as a covariate, average fruit weight was not affected by rootstock in either year in Ontario. In Michigan and Virginia, rootstock and number of fruit per tree, but not the rootstock × number of fruit interaction, were significant, so common slopes models were used to estimate least squares means for average fruit weight. In general, trees on M.27 and P.1 produced the smallest fruit, and trees on B.9, M.9 EMLA, and Mac.39 produced the largest fruit. In New York the interaction of rootstock × number of fruit was significant, so least squares means were estimated at three levels of number of fruit per tree. Both years, at all levels of number of fruit, trees on M.26 EMLA produced the smallest fruit and trees on M.27 EMLA produced the largest fruit. Average fruit weight was most affected by number of fruit per tree when Mark was the rootstock. In general, results were similar when crop density was used as the covariate, except that trees on M.27 EMLA did not produce small fruit in Michigan and Ontario.
Terbacil, a photosynthetic inhibitor, and shade applied to apple (Malus domestica Borkh) limbs and whole trees altered the contents of fruit nonstructural carbohydrates and induced fruit abscission. Shade (92%) from 5 to 15, 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) induced fruit abscission. At 15 and 20 DAFB, fruit from limbs shaded for 10 days contained less total nonstructural carbohydrates (TNC) than fruit from limbs shaded for 0 or 5 days. Terbacil at 50 and 100 ppm applied to whole ‘Redchief Delicious’ trees at 15 DAFB markedly inhibited net photosynthesis. Fruit dry weight, TNC, total sugars, and reducing sugars declined with increasing rates of terbacil and 100 ppm resulted in abscission of all fruit. Trees treated with 0 and 50 ppm retained 4.6 and 1.4 fruit per cm2 of limb cross sectional area (LCSA), respectively. Terbacil at 75 ppm and 92% shade were applied to whole ‘Redchief Delicious’ trees at 18, 23, and 28 DAFB. Fruit dry weight and contents of total sugars and reducing sugars were lowered by shading and terbacil. Shade for 5 or 10 days induced total fruit drop. Terbacil at 75 ppm resulted in 0.8 vs. 2.9 fruit per cm2 of LCSA on the controls. Chemical name used: 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedion (terbacil).
Individual scaffold limbs on 5-year-old ‘Red Prince Delicious’ apple (Malus domestica Borkh.) trees on five rootstocks were unpruned or pruned in Aug. 1981 or Feb. 1982 using three severities at each time. Responses to summer and dormant pruning were similar; no significant interactions occurred. In Dec. 1982, branch circumference was inversely related to pruning severity. Compared to the control, all pruning severities decreased shoot number and increased mean shoot length in 1982; only the most severe pruning suppressed total shoot growth. Flowering and fruiting in 1983 were inversely related to pruning severity.