The effects of rootstock on mid‐season water relations, under orchard conditions of non‐limiting soil moisture, were determined for bearing ‘Empire’ apple trees (Malus domestica Borkh.) on the clonal rootstocks M9, M26, M7, MM106, and MM104 (most to least dwarfing) in their sixth and seventh growing seasons. Stem water potentials (ψstem) of trees on M9 and M26 were more negative at midday, under warm, sunny conditions, than were the trees on the other three rootstocks. However, change in ψstem per change in stem distance through the canopy (water potential gradient) did not vary among rootstocks at midday. There was no rootstock effect on diurnal variation in transpiration or stomatal conductance. Differences in water storage capacitance, relative to tree size, were determined in a separate study but did not account for the differences observed in ψstem. Calculated hydraulic conductivities of xylem water transport suggest that rootstocks differ in their ability to conduct water to the scion, but hydraulic conductivity of the scion was not affected by rootstock. Root‐stock differences in hydraulic conductivity were not accounted for by differences in tree size.
The baseline sensitivity of Monilinia fructicola in a peach orchard not previously exposed to demethylation-inhibiting (DMI) fungicides was determined for propiconazole, using the concentration in an agar medium required to suppress radial growth of mycelium by 50% (EC50) The baseline sensitivity was found to be approximately 0.03 μg/ml. Prolonged, regular exposure of the natural population of M. fructicola to propiconazole in the test orchard over a 3-year period (29 total applications) resulted in a wider range of sensitivity (EC50 of 0.02 to 2.16μg/ml) among isolates than was observed in the initial population (EC50 of 0.02 to 0.15 μg/ml). Comparisons with isolates from commercial orchards where DMI fungicides were used regularly showed that sensitivities were comparable to, or less than, those of isolates from the population in the test orchard that had been exposed to propiconazole for the 3-year period. M. fructicola in South Carolina peach orchards might now be less sensitive to DMI fungicides than when those fungicides were first introduced for brown rot control, although effective disease control in the field has been maintained.
The effect of temperature on ethylene evolution from ethephon-treated sour cherry (Prunus cerasus L. cv. Montmorency) leaves was determined subsequent to foliar application. The upper surface of uniform fully expanded leaves was treated in the field with 125 μg of ethephon, (2-chloroethyl)phosphonic acid. After 24 hours, leaves were detached and ethylene was measured during incubation at temperatures between 10 and 34°C. Ethephon degradation in buffered solutions was also monitored between 10 and 50° and over a range in pH from 3.0 to 7.0. The effect of temperature on rate of endogenous ethylene evolution was examined for sweet cherry shoots and sour cherry leaves, and was calculated for several other tissues and species from values found in the literature. The rate of ethylene evolution from both ethephon-treated leaves and buffered solutions was markedly temperature dependent, with an apparent energy of activation (Ea) of 30 to 32 kcal mole-1. There was no pH-temperature interaction affecting the Ea for buffered solutions. A generalized Ea for endogenous ethylene evolution was about 13 kcal mole-1.
Ethephon, (2-chloroethyl)phosphonic acid, was sprayed at concentrations up to 69.2 millimolar to enhance gum formation in 1-year-old shoots of mature Pruns cerasus L. cv Montmorency trees. Gum accumulation caused rupturing of the shoot periderm, followed by gum extrusion. Lower ethephon concentrations were required to induce gum formation in spring and early summer (1.7-3.5 millimolar) then in late summer and fall (13.8-69.2 millimolar). The number of functional vessels, shoot hydraulic conductance, and water potential of both leaf and internode tissue decreased as gum content of shoots increased. Nontreated control shoots also contained small quantities of gum. There was no difference in neutral sugar composition of gum exuded by the tree, obtained from aqueous shoot extracts, or flushed from the vessels of shoots, whether induced by ethephon or not. Severe decrease in shoot and leaf water potential was associated with shoot die-back. Recovery of xylem function may occur where gummosis is less severe. Discrepancy between measured and predicted hydraulic conductance increased as shoot gum content increased, suggesting that decrease in number of functional vessels alone was not sufficient to explain the effects of gum on loss of shoot hydraulic conductance. Increased gum content in those vessels remaining functional would increase vessel sap viscosity and further reduce hydraulic conductance. The viscosities necessary to account for discrepancy between measured and predicted hydraulic conductance were calculated. Gum concentration less than 1.0%
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.