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Peter D. Petracek, D. Frank Kelsey, and Craig Davis

The effect of high-pressure washing (HPW) on the surface morphology and physiology of citrus fruit was examined. Mature white (Citrus paradisi Macf. `Marsh') and red (Citrus paradisi Macf. `Ruby Red') grapefruit, oranges (Citrus sinensis L. `Hamlin'), and tangelos (Citrus reticulata Blanco × Citrus paradisi Macf. `Orlando') were washed on a roller brush bed and under a water spraying system for which water pressure was varied. Washing white grapefruit and oranges for 10 seconds under conventional low water pressure (345 kPa at cone nozzle) had little effect on peel wax fine structure. Washing fruit for 10 seconds under high water pressure (1380 or 2760 kPa at veejet nozzle) removed most epicuticular wax platelets from the surface as well as other surface debris such as sand grains. Despite the removal of epicuticular wax, HPW did not affect whole fruit mass loss or exchange of water, O2, or CO2 at the midsection of the fruit. Analysis of the effect of nozzle pressure (345, 1380, or 2760 kPa), period of exposure (10 or 60 seconds), and wax application on internal gas concentrations 18 hours after washing showed that increasing nozzle pressure increased internal CO2 concentrations while waxing increased internal ethylene and CO2 concentrations and decreased O2 concentrations. An apparent wound ethylene response was often elicited from fruit washed under high pressures (≥2070 kPa) or for long exposure times (≥30 seconds).

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Thomas R. Gordon, Dorothy Okamoto, Andrew J. Storer, and David L. Wood

Pitch canker, caused by Fusarium subglutinans f. sp. pini, causes branch die-back and stem cankers in many species of pine. Monterey pine (Pinus radiata D. Don), one of the most widely planted pines in the world, is extremely susceptible to pitch canker. Four other pine species, which might serve as alternatives to Monterey pine in landscape settings, were found to be relatively resistant, based on the size of lesions resulting from branch inoculations under greenhouse conditions. Of these species, Japanese black pine (P. thunbergiana Franco) was the most resistant, followed by Canary Island pine (P. canariensis Sweet ex K. Spreng), Italian stone pine (P. pinea L.), and Aleppo pine (P. halepensis Mill.). Consistent with these findings, a field survey conducted in Alameda County, Calif., revealed Monterey pine to have the highest incidence of infection, with significantly lower levels in Aleppo, Canary Island, and Italian stone pines. Japanese black pine was not observed in the survey area.

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E.W. Stover and D.W. Greene

Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.

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Frank G. Bethea Jr., Dara Park, Andrew Mount, Nick Menchyk, and Haibo Liu

the uptake of foliar-applied chemicals in several plant species under various environmental conditions ( Fernandez et al., 2006 ; Liu, 2004 ; Neal et al., 1990 ). For example, surfactant added to potassium nitrate applications increased potassium

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Vladimir Orbović, Diann Achor, and James P. Syvertsen

; Schreiber and Schönherr, 1990 ). Thus, the dynamics of cuticular penetration can yield insights into foliar uptake ( Orbović et al., 2001a ) or uptake into the fruit tissue. The organosilicone surfactant, L-77, has a high surface activity, which results in

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R.E. Byers, J.A. Barden, R.F. Polomski, R.W. Young, and D.H. Carbaugh

X-77 surfactant; Sharon Myers, Raymond Myers, and Philip Ramsey, Dept. of Statistics, VPI & SU, for statistical assistance and analysis. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations

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Jeffrey G. Williamson and D. Scott NeSmith

used the nonionic surfactant X-77 at 0.25% (v/v). After flowering was complete, plants were moved to a greenhouse for the remainder of the experiment. Percent fruit set and average individual berry weight were determined for each treatment. Fruit set

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Fazeeda N. Hosein, Adrian M. Lennon, and Pathmanathan Umaharan

supplemented with 0.05% of the surfactant S240 (Break Thru TM ; Evonik Goldschmidt Chemical, Hopewell, VA) and 100 μM acetosyringone (Sigma-Aldrich, St. Louis, MO). The explants were immersed in the infiltration solution for 4 h immediately after cutting and

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Hazel Y. Wetzstein and S. Edward Law

comprising stigmatic exudates indicates that substances may differ in polarity, molecular weight, and solubility. Wash treatments evaluated included various buffer solutions, surfactants, dilute acids and bases, and solvents. This article describes a method

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Vincent A. Fritz, Veronica L. Justen, Ann M. Bode, Todd Schuster, and Min Wang

® 20 surfactant (Sigma-Aldrich) and applied at the following concentrations: 0.1 m m , 0.2 m m , and 0.2 m m split application. The three JA treatment rates plus a surfactant and water control were applied as a foliar spray in excess at 31 cm above the