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Bruce D. Lampinen

Although capillary rise plays an important role in providing water to cranberry plants, the relation between water level and plant establishment and growth has not been adequately studied. The aim of this study was to maintain constant water levels and to monitor the effects on establishment, root growth, and aboveground growth in greenhouse-grown cranberries. Cuttings from cranberry (Vaccinium macrocarpon Ait.) cultivar Stevens were rooted in sand-filled pots in the greenhouse for ≈2 weeks and then transplanted to sand-filled PVC tubes. The water level in the tubes was set 7.5, 15, 22.5, 30, or 37.5 cm below the top of the sand surface. Pan evaporation was estimated using PVC tubes filled with water to the same level as the sand in the planted tubes. Extension growth of uprights and runners was measured every 3 days. After growing in the PVC tubes for 90 days, all plants were harvested and upright length, runner length, leaf dry weight, stem dry weight, root length, and root dry weight were measured. There was a similar mortality rate among plants in all of the treatments. Water use varied among the treatments, with the 7.5-cm water level treatment using the least water. The 15-cm water level used the most water, with water use then decreasing in a linear fashion for the 22.5-, 30-, and 37.5-cm treatments. At the conclusion of the study, aboveground dry weight was significantly less for plants in the 7.5-cm treatment compared to any of the other treatments, while it was highest in the 15-cm water level treatment and decreased with lower water levels in a linear fashion as did the average daily water use. The patterns of root dry-weight accumulation were different among the treatments with the highest accumulation in the 22.5-cm water level treatment and decreasing root dry weight with both higher and lower water level treatments. This study points out the detrimental effects of a too high water table, but it also shows that there are costs associated with establishing a deeper rooting system. The benefit of the deeper root system probably outweighs the cost of production however, since shallow root systems lead to increased susceptibility to drought stress and decreased access to nutrients.

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Bruce D. Lampinen and Kenneth A. Shackel

Two levels of deficit irrigation were applied to mature French prune trees based on gradually declining midday stem water potentials decreasing to –1.5 MPa (moderate stress) and –2.5 MPa (severe stress) by harvest. The moderate and severe stress treatments resulted in 32% and 51% water savings, respectively, compared to the fully irrigated control. The average photosynthetic rate and dry fruit yield for the moderate stress treatment were not significantly lower than those for the fully irrigated control. The severe stress treatment had significantly lower photosynthetic rates from late morning until sunset on most days. However, this lower photosynthetic rate did not result in significantly lower dry fruit yields. There were no significant differences in light interception as measured diurnally or over the course of the season in the first year of the study. However, light interception and photosynthetic differences might be expected to be more pronounced in subsequent years, due to carryover effects.

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Thomas M. Gradziel, Bruce Lampinen, Joseph H. Connell, and Mario Viveros

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Sergio Tombesi, Bruce D. Lampinen, Samuel Metcalf, and Theodore M. DeJong

Almond spurs are known to be the primary bearing unit in almond tree and are subject to alternate bearing. Fruits are a strong sink in bearing spurs and can influence spur leaf growth. At the same time the percent of flowers that set fruit on a spur (spur relative fruit set) could be influenced by the competition among multiple flowers/fruits borne on the same spur as well as by limited leaf area on the same spur. The aim of the present work was to investigate the relationship between current-year spur leaf area and spur absolute and relative fruit set. Approximately 2400 spurs were tagged and followed over 6 years and data concerning spur leaf area, number of flowers per spur, and number of fruits per spur were collected. Spur leaf area was reduced in fruiting spurs in comparison with non-fruiting spurs according to the number of fruits borne by each spur. This phenomenon contributes to spur alternate bearing because spur flowering and survival in the next year are a function of the leaf area in the current year. Relative fruit set in almond appears to be negatively associated with current-year spur leaf area. Competition among fruits on the same spur did not appear to influence spur relative fruit set.

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Bruce D. Lampinen, Kenneth A. Shackel, Stephen M. Southwick, Bill Olson, James T. Yeager, and Dave Goldhamer

The sensitivity of French prune (Prunus domestica L. syn. `Petite d'Agen') to water deprivation at various fruit growth stages was studied over 3 years in a drip-irrigated orchard. The soil was a poorly drained Rocklin fine sandy loam with a hardpan that varied from 4.75 to I m from the surface at the northern end of the orchard (shallow soil condition) to no hardpan apparent to 2 m below the surface at the southern end of the orchard (deep soil condition). Water deprivation during a) the first exponential phase of fruit growth or stage I, b) lag phase of fruit growth or stage II, c) first half of stage II, d) second half of stage II, e) second exponential fruit growth phase or stage III, and f) postharvest was compared to a fully watered control. Water deprivation caused the most severe reduction in tree water status when it was imposed over longer periods of time and during periods of high evaporative demand and also had mm-e severe effects under shallow soil conditions. Compared to the control treatment, deprivation during all of stage II (the most severe deprivation treatment) was associated with increased Ilowering, reduced fruit hydration ratio, and smaller fruit size under all soil conditions. Under deep soil conditions, deprivation during all of stage II resulted in increased return bloom, which was reflected in higher fruit loads and dry t-ha-' fruit yield. However, under shallow soil conditions, even though return bloom was increased with this treatment, fruit loads and dry t·ha-1 fruit yields were the lowest of all treatments. These differences in treatment effects in shallow vs. deep soil conditions were most likely the result of increased fruit drop, which occurred under shallow soil conditions as a result of rapid onset and increased severity ofstress. Treatments that had parallel effects in shallow and deep soil conditions resulted in statistically significant overall treatment effects, while those that had opposing effects in shallow vs. deep soil conditions did not show significant overall treatment effects. Substantial alternate hearing occurred, and, in general, dry fruit yields above ≈9 dry t·ha-1 resulted in a decrease in fruit load the following year, while loads below this value showed a subsequent increase. Based on a separate estimate of the theoretically stable value for each treatment, all deprivation treatments resulted in a higher sustainable fruit load compared to the fully irrigated control. This suggests that, for the purpose of prune fruit production, there may be an optimal level of tree water stress.

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Bruce Lampinen, K. A. Shackel, S. Southwick, D. Goldhamer, and B. Olson

During this three year study, irrigation water was withheld from trees in a commercial drip irrigated french prune orchard (Butte County, CA), during different periods within the double sigmoid fruit growth pattern (stage I - III), and postharvest. Tree water stress associated with early season water deprivation was minimal, due to the presence of stored soil moisture and low evaporative demands. For mid and late season water deprivation there was no fruit growth stage that was particularly sensitive to water stress, although severe and prolonged stress caused smaller fruit with lower quality. For the three year average, irrigation treatments caused no statistically significant effects on fruit set or drop relative to the control, however most of the stress treatments increased return bloom relative to the control, resulting in higher fruit loads and higher yields. These results suggest that moderate water stress may enhance economic prune productivity.

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Richard P. Buchner*, Allan Fulton, Bruce Lampinen, Ken Shackel, Terry Prichard, Larry Schwankl, Sam Metcalf, and Cayle Little

Ninth leaf California Chandler Walnuts (Juglans regia) on Northern California Black (Juglans hindsii) or Paradox (English/black hybrid) rootstock were irrigated to achieve three levels of Midday Stem Water Potential (MSWP). Target potentials were: 1) low water stress (average MSWP of -3.2 bars); 2) mild water stress (average MSWP of -6.2 bars); and 3) moderate water stress (average MSWP of -7.3 bars). Stem Water Potential was measured midday (12-4 pm) by placing leaves inside water impervious, light blocking foil bags. Leaves remained bagged for at least ten minutes to achieve equilibrium. Bagged leaves were removed, placed inside a pressure chamber and stem water potential was measured at endpoint. Data are presented for the 2002 and 2003 seasons. Withholding irrigation water had a significant impact on `Chandler' growth, productivity, and profitability particularly on young, vigorously growing trees. Chandler/Black appears to be more tolerant to water stress compared to Chandler/Paradox For Chandler on Paradox, water stress significantly reduced growth, yield, price per pound, percent edible kernel, and resulted in darker kernels. In addition, water stress significantly increased the total percent offgrade. Withholding irrigation does not appear to be a good strategy in young, vigorously growing `Chandler' orchards. Mature trees and trees grafted onto Northern California black rootstock may be more tolerant of moisture stress.

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Aude Tixier, Adele Amico Roxas, Jessie Godfrey, Sebastian Saa, Dani Lightle, Pauline Maillard, Bruce Lampinen, and Maciej A. Zwieniecki

Temperature is assumed to be the principal regulatory signal that determines the end of dormancy and resumption of growth. Indirect evidence that stem temperature interferes with phenology comes from the common orchard practice of painting stems to protect them from disease. This work studies the effects of application of white paint to the stems of persian walnut (Juglans regia) trees on winter stem temperature, carbohydrate content, and spring phenology. Painting bark resulted in the delay of budbreak by several days, higher nonstructural carbohydrate (NSC) concentrations in the bark and wood of painted extension shoots and changes in the spatial gradients of NSC during budbreak. The demands of maintenance respiration exceeded mobilization from local carbon pools during bud development suggesting a potential role of carbohydrate transport during spring budbreak in persian walnut. Painting provides an exciting perspective for mitigating effects of milder winter in orchards. The effect of reducing diurnal and spatial temperature variability limits early budbreak, NSC depletion associated with intense maintenance respiration, freeze–thaw cycles and frost dehardening.