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  • Author or Editor: J.A. Flore x
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The source-sink ratio of l-year-old, potted `Montmorency' sour cherry (Prunus cerasus) trees was manipulated by partial defoliation (D) or continuous lighting (CL) to investigate the phenomenon of end-product inhibition of photosynthesis. Within 24 hours of D, net CO2 assimilation rate (A) of the most recently expanded source leaves of D plants was significantly higher than nondefoliated (control) plants throughout the diurnal photoperiod. Between 2 and 7 days after D, A was 30% to 50% higher and stomatal conductance rate (g,) was 50% to 100% higher than in controls. Estimated carboxylation efficiency(k) and ribulose-1,5-bisphosphate (RuBP) regeneration rate increased significantly within 2 days and remained consistently higher for up to 9 days after D. Leaf starch concentration and dark respiration rate decreased but sorbitol and sucrose concentration increased after D. The diurnal decline in A in the afternoon after D may have been due to feedback inhibition from accumulation of soluble carbohydrates (sucrose and sorbitol) in the cytosol. This diurnal decline indicated that trees were sink limited. By 9 days after D, photochemical efficiency was significantly higher than in control plants. In the long term, leaf senescence was delayed as indicated by higher A and gs in combination with higher chlorophyll content up to 32 days after D. CL resulted in a significant reduction of A, gs, k, variable chlorophyll fluorescence (Fv), photochemical efficiency, and estimated RuBP regeneration rate of the most recently expanded source leaves within 1 day. During the exposure to CL, A was reduced 2- to 3-fold and k was reduced up to 4-fold. The normal linear relationship between A and gs was uncoupled under CL indicating that A was not primarily limited by gs and since internal CO2 concentration was not significantly affected, the physical limitation to A imposed by the stomata was negligible. The decrease in Fv and photochemical efficiency indicated that leaves were photoinhibited within 1 day. The decrease in instantaneous chlorophyll fluorescence after at least 1 day of CL indicated that there was a reversible regulatory mechanism whereby the damage to photosystem II reaction centers was repaired. Leaf chlorophyll content was not altered by 1,2, or 3 days of exposure to CL, indicating that photooxidation of chlorophytl did not occur. The time to full photosynthetic recovery from CL increased as the duration of exposure increased. CL plants that were photoinhibited accumulated significant starch in the chloroplast in a companion study (Layne and Flore, 1993) and it is possible that an orthophosphate limitation in the chloroplast stroma was occurring. D plants that were continuously illuminated were not photosynthetically inhibited. After 7 days of CL, plants that were then partially defoliated yet remained in CL photosynthetically recovered within 5 days to pre-CL values. Under the conditions of this investigation, end-product inhibition of A occurred in young, potted sour cherry trees but the mechanism of action in D plants was different than in CL plants.

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The leaf surface area of l-year-old, potted `Montmorency' sour cherry (Prunus cerasus L.) trees was reduced by punching disks from some or all leaves to determine the threshold level of leaf area removal (LAR) necessary to reduce net CO2 assimilation (A) and whole-plant growth. Removal of 30% of the leaf area of individual leaves reduced A on a whole-leaf basis between 1 and 3 weeks following LAR. Less than 30% LAR was compensated for by higher estimated carboxylation efficiency and ribulose-l,5-bisphosphate (RuBP) regeneration capacity. The threshold level of LAR based on gas exchange of individual leaves was 20%. Although whole-plant dry weight accumulation was reduced at all levels of LAR, a disproportionately large decrease in dry weight occurred as LAR increased from 20% to 30%. This result indicates that 30% LAR exceeded the threshold LAR level that was noted for A (20% LAR). Wound ethylene production induced by leaf-punching ceased after 24 hours, which indicated that wounds had healed and that ethylene, therefore, did not influence A significantly. The observed threshoId of 20% LAR represents a significant compensation ability for sour cherry, but this threshold may change with crop load, environment, or both.

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The influence of increasing levels of trunk damage on vegetative and reproductive capacity of 3- to 5-year-old `Montmorency' sour cherry (Prunus cerasus L.) trees was determined for three seasons. Removal of or damage to bark up to halfway around the trunk circumference minimally affected growth and productivity. The total wound callus produced per tree was related to wound size. Wound repair was variable depending on the type or extent of injury. Removal of damaged bark greatly reduced wound repair. Girdling 75% or 100% of the trunk circumference resulted in no tree mortality at one site and 17% and 50% mortality, respectively, at another. Differentiated phloem in wound callus of trees with 100% bark removal and survival 4 years following injury indicated that vascular reconnection occurred across wounds.

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Abstract

One-year-old peach [Prunus persica (L.) Batsch cv. Redhaven] trees were grown outdoors under 4 different shade levels (100%, 36%, 21%, and 9% of full sun). Shoot length, internode length, and node number were unaffected by shade, but heavy shade (9% full sun) reduced stem diameter 24%. Compared to those in full sun, average leaf areas were increased 18%, 30%, and 20% by 36%, 21%, and 9% shade, respectively. Shading caused a more horizontal leaf orientation and lower specific leaf weight. Both average and maximum photosynthetic rate per unit area or per mg chlorophyll decreased with shading, but increased with shading when expressed per unit dry weight. Chlorophyll content per unit leaf area increased with shading, but stomatal resistance was unaffected. Leaves from shade treatments became light-saturated between 400 and 600 µEs-1m-2; full-sun leaves became light-saturated at 700-900 µEs-1m-2.

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Terbacil (100 ppm) was applied to mature Redhaven (Prunus persica L. Batsch), once, or twice in different combinations during stage I, II, or III of fruit development or after harvest to determine the effect of photosynthetic inhibition on abscission, fruit size, yield, and shoot growth of the current seasons crop, and winter hardiness, tree carbohydrate status, and return bloom and fruit set the following year. Following application all trees were thinned to the same level in the middle of stage II. Field determinations indicated terbacil inhibited photosynthesis to 0-20% of the control within 24 h, and that leaves recovered to 85-95% within 7-10 days. Fruit thinning was related to the time of application, however, there were no significant differences in crop load at harvest. Fruit size, yield and maturity were inversely related to the time of application. Cold hardiness of the shoots was reduced significantly by Nov. 30 for all applications. Carbohydrate and 1993 fruit set analysis are incomplete at this time. This study indicates that stress early in the season has a greater effect on the current season crop than a similar stress later in the season.

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Abstract

S-ethyl dipropylthiocarbamate (EPTC, 2.24 kg/ha) inhibited epicuticular wax production by developing leaves of cabbage (Brassica oleracea L. capitata group cv. Market Prize). Similar inhibition of wax deposition was observed on abaxial (66.5%) and adaxial (67.5%) leaf surfaces. Wax bloom was absent on EPTC-treated plants, and its absence was associated with a marked reduction in surface fine-structure. No significant changes in cuticle thickness, structure, or morphology were observed due to EPTC-treatment as indexed by staining with Sudan III and IV and viewing with plane-polarized light. EPTC did not significantly affect the total weight of the cuticular membrane, cuticular wax, or cutin matrix, but there was a significant increase in the carbonate plus water soluble fraction (+33.4 μg/cm2), which approximately equaled the decrease in epicuticular wax weight (–28.8 Mg/cm2).

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Abstract

S-Ethyl dipropylthiocarbamate (EPTC, 2.24 kg/ha) altered wax composition on developing leaves of cabbage [Brassica oleracea L. (Capitata group) cv. Market Prize], but did not affect cutin composition. The alkane, ketone and secondary alcohol content of the epicuticular wax was reduced and ester content increased. C29 constituents (alkane, ketone, aldehyde and sec-alcohol) accounted for 72.5% (34.1 μg/cm2) and 40.2% (7.2 μg/cm2) of the epicuticular wax on control and EPTC-treated leaves respectively. Homlog composition within a chemical group was not changed. Chemical composition was similar for abaxial and adaxial leaf surfaces, and the EPTC-induced change in chemical composition was similar for both surfaces. In contrast with epicuticular wax, cuticular wax contained higher percentages of fatty acids and primary alcohols, and lower percentages of alkanes, and ketones. All constituents except the unidentified polar materials and fatty acids were lower in cuticular wax extracted from EPTC-treated than non-treated plants. The main component of the cutin fraction from both control and EPTC-treated plants was identified as dihydroxyhexadecanoic acid. Cutin acids were not quantitatively changed by the EPTC treatment.

Open Access

We have developed a system of automated intermittent salt application above the tree during a rain event that has shown very encouraging results (Washington State Hort Soc. Proc. 1995, Good Fruit Grower, vol. 47; pp. 23-24; Acta Hort. vol. 468 pp. 649 & 683) in Michigan and the Pacific Northwest. In 1998, we significantly reduced rain cracking with the system used in previous years. At the Southwest Michigan Research and Extension Center (SWMREC), on `Ulster', the control averaged 18% while the 0.5% calcium chloride had 6.7% cracks. Similar results were found for `Ulster', `Somerset', and `Rainer' at the Northwest Station. Cracking was greater in the upper part of the tree than the lower part for the control. The calcium chloride had less cracking on the upper part than the lower part indicating that calcium chloride applied from above the tree was not uniformly distributed to the lower part of the canopy in high enough concentrations. Multiple emitters per tree decreased this problem. We determined that there was an interaction with temperature. More fruit cracked at high temperature than low temperature. In the field more fruit cracked during the day than at night. We attribute this to the difference in day and night temperature. Using a bioassay system we able to determine the critical concentration of salt that must be on the fruit to inhibit water uptake and rain splitting up to a 4-h period. It ranged between 0.05% to 0.10 % depending on the variety and stage of development.

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Abstract

Soluble lipids from periderm of carrot (Daucus carota L. cv. ‘Danvers’) were not decreased significantly by foliar sprays of linuron, chlorpropham, ethofumesate, or Stoddard oil applied to field plots. Ethofumesate treatments to ‘Scarlet Nantes’ grown in the greenhouse produced significant reductions in isolated periderm weight per unit area. This decrease occurred both in the chloroform/methanol-soluble and insoluble fractions. The diffusion resistance of treated roots was lower significantly than controls.

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Abstract

Net photosynthetic rate (Pn) of leaves of sour cherry (Prunus cerasus L. cv. Montmorency) was greater for leaves between nodes 9 and 13 than for either older, mature leaves or newly expanding leaves on the same shoot. For individual leaves, Pn reached maximum when the leaf was greater than 80% expanded, remained constant for 2 to 4 weeks, then gradually declined. Hyperbolic and parabolic response curves were observed in response to light and temperature, respectively. Maximum Pn occurred at light intensities between 800–1200 μEm−2s−1. Optimum temperature ranged with light level and vapor pressure deficit (YPD), but was generally between 15 to 30°C. Pn increased as CO2 concentration increased between 0 and 600 ppm, the CO2 compensation point being about 80 ppm. Under optimum conditions Pn ranged between 30 to 35 mg CO2 dm−2 hr−1.

Open Access