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L. Lombardini and J.A. Flore

The recent development of small portable infrared thermometers has made canopy temperature an easily measured characteristc in the field. Our objective was to correlate a reduction of soil water with foliage temperature and to compare it with other indicators of plant stress (Pn, E, gs, leaf expansion, sap flow). During Summer 1998, we evaluated the responses of potted apple rootstocks (cultivars Budagowski 9, M9, and Mark) to soil water deficit. Irrigation was withheld for 7 days, and the canopy temperature (Tc) was measured daily with an infrared camera. Tc was always higher than air temperature (Ta). Tc between control and stress plants began to differentiate from day 3. In Mark, this difference was maintained until the end of the experiment. However, gas exchange in Mark seemed to be less affected by the stress than in the other two cultivars. At day 7, midday stomatal conductance (gs) was 38.0, 32.3, and 72.0 mmol·m–2·s–1 in Budagowski 9, M9, and Mark, respectively (control values varied between 161.6 and 164.3 mmol·m–2·s–1 for all the cultivars). Heat-pulse sapflow sensors installed on Mark indicated that the speed of the xylem sap was affected by the stress from day 4 (19-26 cm/h for the controls vs. 15–21 cm/h for the stressed plants). Specific details on the physiological data will be presented.

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J.A. Flore and Desmond Layne

Resource partitioning between individual sink organs is dependent upon the supply of carbon from current photosynthesis and reserves, the relative ability of the translocation system to deliver resources to the sinks, and the strength or competitive ability of the sinks. To comprehend photoassimilate distribution in Prunus, one must have a general understanding of habitat, growth patterns, and changes in sink demand over the life cycle and seasonal development of the plant. In this review, we describe assimilation rates for the major Prunus species and general dry matter allocation patterns, with emphasis on environmental and biological factors that effect photosynthesis, partitioning, and control. The following factors will be covered: annual growth, changes with tree age, environmental and biological factors that effect photosynthesis, genetic factors, water, light, fruiting, and pruning.

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J. A. Flore and Edgardo Disegna

Terbacil an inhibitor of photosynthesis was applied to 10-year-old `Redchief' apple trees in the field carrying a heavy or light fruit crop, or to trees in pots. This simulated the effect of photosynthetic inhibition (PN-I) by either biotic or abiotic stress. Current as well as the next season's crop and physiology were determined. The magnitude and duration of photosynthetic inhibition was dose-dependent. A concentration of 63 mg·liter–1 was applied at 15-day intervals from bloom through harvest. Photosynthesis was in inhibited by 50% to 80% within 24 h of application, but recovered to control levels 10 to 14 days later. Terbacil at 15 and 30 DAFB induced fruit abscission, but not at later dates. The earlier the application the greater the effect on current seasons yield and fruit size. There was also a significant interaction with crop load. There were no significant effects on fruit soluble solids, fruit firmness, fruit density, or fruit color at harvest. Terbacil did not affect cold acclimation, deep winter hardiness, or deacclimation. Pn inhibition at 30, 60, 80, and 100 DAFB reduced return bloom.

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S.L. Breitkreutz and J.A. Flore

Pest damage to apple fruit is intolerable by our current standards. However, the effects of foliar damage on the plant's physiological status and fruit quality are not thoroughly understood. The objective of this work was to determine the time during the growing season when apple trees are most susceptible to foliar damage. Terbacil (50 ppm), an inhibitor of photosynthesis, was applied to 8-year-old `Gala'/Mark planted at 6 ×18-foot spacing or 14-year-old `Empire'/M106 planted at 18 × 20-foot spacing at 20- to 30-day intervals from petal fall until harvest to simulate environmental or biological stress. The work was conducted from 1995 through 1998. Photosynthesis was inhibited by 50% to 80% within 24 h of application of Terbacil but recovered to control levels 10 to 14 days after. The fruit were evaluated at harvest for total yield, size of fruit, and fruit number. Terbacil induced fruit abscission when applied at petal fall but not at later dates. The earlier the application, the greater the effect on current seasons yield and fruit size depending on crop load. For `Gala', there was a reduction in yield at petal fall of 30% to 70% over the control trees. Further detailed results will be presented.

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Matt Reed, Brie Genter and J.A. Flore

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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J.A. Flore and D.R. Layne

The objective of this experiment was to design orchard systems and tree shapes that optimize production based upon light interception. `Montmoreney' on `Mahaleb' rootstock was established at the Clarksville Horticultural Research Station in 1982. The following factors were investigated: a) tree shape; free form, Δ triangle and • rectangle, b) tree height to clear alleyway width ratios; 1.5, 2.0 and 2.5, and c) tree density 3.0×4.5 m, 3.0×6.0 m. Tree shape was established beginning in the 3rd leaf by summer hedging on an annual basis at the end of stage II of fruit growth. Beginning with the 4th leaf, light interception in each system was estimated by measuring the light interception below the canopy at hourly intervals after full canopy development. In 1989, yields ranged from 14,000 to 22,000 Kg ha-1. Ripening was delayed for rectangle shaped trees, with a height to clear alleyway, width ratio of 1.5, spaced 3.0×4.5 m, likely because hedging reduced leaf to fruit ratios. Within a tree form, yield was linearly related to % light interception, however rectangular trees were more productive than triangle shaped trees. The relevance of this study to orchard design will be discussed.

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Desmond R. Layne and J.A. Flore

A series of experiments were conducted with one-year-old potted sour cherry trees to evaluate the effects of source reduction (removal of 70% of the expanded leaves = Defol.) or source enhancement (continuous illumination = C.L.) on source leaf gas exchange. There was a significant increase in net CO2 assimilation (A) and stomatal conductance (gs) of Defol. within one day in contrast to the non-defoliated control (Cont.). Defol. had lower daily dark respiration rates (Rd) and higher A values throughout the 14 h diurnal photoperiod than Cont. Defol. had daily assimilation rates 50% higher than Cont. in as early as 3 days. One month later, specific leaf weight, leaf chlorophyll and A was higher in Defol. Non-defoliated plants were also placed under either a 14 h photoperiod (Cont.) or a 24 h photoperiod (24h). A of 24h was reduced from Cont. by 50% after one day. The diurnal response of A in Cont. was removed when plants were put in C.L. Following 7 days in C.L., 70% defoliation of 24h plants resulted in a complete recovery from photosynthetic inhibition within 48 hours. The short-term effects of source manipulation on photochemical and carboxylation efficiencies, photorespiration and stomatal limitations will also be addressed.

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J.A. Flore and Desmond R. Layne

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Desmond R. Layne and J.A. Flore

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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Desmond R. Layne and J.A. Flore

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.