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- Author or Editor: John A. Barden x
Abstract
Two experimental growth regulators, CGA-15281 (beta-chloroethyl-methyl-bis-benzyloxy-silane) and an analogue, CGA-17856, induced leaf abscission in peach (Prunus persica (L.) Batsch). Responses paralleled temperature following treatment. Older leaves were more responsive than younger ones and abscission occurred prior to leaf senescence. Applications prior to rainfall indicated about 6 hours without wetting was needed for maximum chemical activity. CGA-17856 tended to cause more leaf abscission than CGA-15281.
Abstract
Summer pruning significantly restricted radial growth of trunks, shoot growth, and root growth of young trees of ‘Delicious’ apple (Malus domestica Borkh.) the year of treatment. Summer pruning early in the season was most devitalizing. Application of naphthaleneacetic acid (NAA) to the pruning cut after summer pruning had inconsistent effects on dry weight accumulation, but usually reduced regrowth. Growth of summer-pruned trees was generally similar to growth of comparably dormant-pruned trees the year following treatment.
Abstract
Several summer pruning treatments were applied in August to ‘Stayman’/Malling Merton (MM) 111 apple (Malus domestica Borkh.) trees measuring 4m high and 5m wide to examine the resulting changes in light climate. Diffuse photosynthetically active radiation (PAR) increased immediately by about 1/5 on the periphery and 1/10 within the canopy from 2 types of summer pruning. These changes in PAR had no effect on net photosynthetic (Pn) potential, dark respiration (Rd), or specific leaf weight (SLW) determined 21 and 54 days after pruning. One method of summer pruning reduced penetration of PAR into inner canopy positions the year following treatment.
Abstract
‘Delicious’, ‘Golden Delicious’, and ‘Stayman’ apple trees (Malus domestica Borkh.) were summer pruned in late June or mid-August. Fruit were smaller on June- or August-pruned ‘Stayman’ trees than on comparable dormant-pruned control trees. Summer pruning had little effect on the size of ‘Delicious’ and ‘Golden Delicious’ fruit. Soluble solids were suppressed within 2 weeks after summer pruning on all cultivars, but fruit firmness was unaffected. Summer pruning slowed the rate of starch disappearance from fruit flesh. Preharvest drop, severity of watercore, and bitter bit were suppressed by summer pruning. Calcium concentration of fruit flesh was not significantly increased by summer pruning. Yield, expressed as total fruit weight or number of fruit per tree, was not consistently influenced by summer pruning over a 2-year period.
Abstract
Young container-grown apple (Malus domestica Borkh.) trees and mature bearing trees were summer pruned either before or after shoot extension had ceased. Net photosynthesis, dark respiration, and transpiration of shoot leaves were increased by summer pruning, while stomatal resistance was decreased as compared to dormant pruned controls. These effects were more pronounced and of longer duration in basal leaves of container-grown trees and interior leaves of orchard trees than in distal or peripheral leaves, respectively.
Abstract
Changes in photosynthetic parameters in ‘Stayman’/Malling Merton (MM) 111 apple (Malus domestica Borkh.) trees measuring 5 m wide and 4 m high were studied for an entire growing season. Parameters investigated included penetration of photosynthetically active radiation (PAR), changes in spur leaf net photosynthetic (Pn) potential, dark respiration (Rd) and specific leaf weight (SLW). As measured by changes in PAR penetration, canopy development was generally complete by mid-May. Pn, Rd, and SLW were modified by canopy position. SLW was influenced by the previous light environment as peripheral canopy leaves had higher SLW’s than interior leaves.
Abstract
There was no effect of rootstock on the net photosynthesis (Pn) of 1-year-old vegetative, containergrown ‘Delicious’ trees in 2 experiments. Rootstock effects on specific leaf weight (SLW) were slight in one experiment, and absent in another. There was no influence of rootstock on shoot growth, leaf number, transpiration rate (Tr) or dark respiration (Rd), each of which was determined in one experiment. These data fail to support reports of differences in Pn within a given cultivar on various rootstocks.
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.
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.