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  • Author or Editor: Carl E. Sams x
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Field-grown dogwood trees in a commercial nursery were sprayed with 0%, 1%, or 2% soybean oil emulsified with Latron B-1956 at 2-week intervals from 10 June until 19 Aug. 1998. In 1999, dogwood trees were sprayed with 0%, 1%, 1.5%, 2%, or 2.5% emulsified soybean oil at 2-week intervals from 22 June until 26 Aug. The trials had treatments arranged in randomized complete-block designs with eight trees per block and six and four replications in 1998 and 1999, respectively. Disease severity of powdery mildew was estimated using the following scale: 0 = healthy, 1 < 2%, 2 < 10%, 3 < 25%, 4 < 50%, 5 > 50%, and 6 = 100% of foliage with symptoms or signs of powdery mildew. In 1998, trees sprayed with soybean oil had higher net photosynthesis rates and more caliper and height growth than control trees. Untreated trees and ≈25% of foliage infected with powdery mildew on 8 July, while trees sprayed with 1% or 2% soybean oil had about 2% of leaves infected. In 1999, the powdery mildew was already present on foliage (wet spring) when the first application of oil was made. Repeated sprays of soybean oil did not reduce the incidence of powdery mildew. Thus, soybean oil appeared to provide protective control of powdery mildew but not curative control of a heavy infestation of the fungi. Photosynthesis was increased by soybean oil for the first month of spraying in 1999, but did not differ after that. Repeated applications of even the high rates of oil did not cause phytotoxicity.

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Treatments of dormant oil, at rates of 0, 3, 6, 9, or 12 % (v/v), were sprayed until drip on four year old `Biscoe' peach trees on February 6, 1990. Another treatment was applied as a split application with 6 % applied on the previous application date and a second application of 6% solution applied on February 12. The internal atmosphere of bud and twig was modified by the oil treatment. The internal concentration of CO2 was elevated the morning following treatment and continued higher than the control for seven days. A second application Of 6% oil resulted in additional elevation of internal CO2. External evolution of CO2 of all oil treated twigs was 6 to 18% lower than the control 8 days after treatment. Bud phenology and bloom date of trees receiving higher rates of oil were slightly delayed.

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One important regulator that coordinates response to environmental stress is the hormone abscisic acid (ABA), which is synthesized from xanthophyll pigments. Despite the fact that there is strong evidence of increases in ABA concentrations under various environmental stresses, information concerning the effects of exogenous ABA applications on leaf pigments and fruit carotenoids in tomato (Solanum lycopersicum) is lacking. This study investigated the impacts of root tissue ABA applications on tomato leaf and fruit pigmentation concentrations of ‘MicroTina’ and ‘MicroGold’ tomato plants. Tomato plants were treated with increasing concentrations of ABA in the nutrient solution. Therefore, the purpose of this study was to determine dose–response effects of ABA treatment in solution culture for maximum leaf pigmentation and fruit carotenoids in two distinct genotypes of dwarf tomato. Because ABA is a product of the carotenoid biosynthetic pathway, we hypothesized that applications of ABA treatments would have a positive impact on leaf chlorophylls and carotenoids. Applications of ABA treatments may also have a positive impact on tomato fruit carotenoids. The results indicated that ‘MicroTina’ plants treated with ABA (0.5, 5.0, and 10.0 mg·L−1) had a significant increase in β-carotene [BC (P ≤ 0.001)], lutein [LUT (P ≤ 0.001)], zeaxanthin [ZEA (P ≤ 0.05)], and neoxanthin [NEO (P ≤ 0.001)] in the leaf tissue. In ‘MicroGold’ tomato plants, carotenoids responded similarly. For example, there were significant increases in BC (P ≤ 0.01), LUT (P ≤ 0.001), ZEA (P ≤ 0.05), and NEO (P ≤ 0.001). In ‘MicroTina’ tomato leaves, there were significant increases in chlorophyll a [Chl a (P ≤ 0.001)] and chlorophyll b [Chl b (P ≤ 0.001)] concentrations. Furthermore, there were significant increases in Chl a (P ≤ 0.001) and Chl b (P ≤ 0.001) in ‘MicroGold’ leaf tissue. In ‘MicroTina’ tomato fruit tissue, the concentration increased significantly for lycopene [LYCO (P ≤ 0.01)]. However, in ‘MicroGold’, there were no significant changes in BC and LUT concentrations. In addition, LYCO was found to be below detection limits in ‘MicroGold’ tomato fruit. Therefore, ABA has been shown to positively change tomato leaf pigments in both genotypes and fruit tissue carotenoid concentrations in ‘MicroTina’ tomato.

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Three polyamine biosynthesis inhibitors, α-difluoromethylornithine (DFMO), α-difluoromethylarginine (DFMA), and α-methylornithine (MeOrn), alone and in combination with CaCl2, were tested for their ability to reduce in vitro growth and soft rot development in apple (Malus domestica Borkh.) fruit caused by Botrytis cinerea Pers.:Fr. and Penicillium expansum Link. All three inhibitors reduced the in vitro growth of the pathogens. Calcium had no effect on fungal growth in vitro. Pressure infiltration of millimolar concentrations of DFMO or DFMA or 25 g·L-1 CaCl2 solutions into apples reduced subsequent soft rot development by B. cinerea and P. expansum >40%. A combination treatment of Ca and DFMO or DFMA reduced decay >67%. Treatment of apples with MeOrn was less effective at inhibiting decay development. None of the inhibitors affected polyamine levels in apple cortical tissues. Some injury to the fruit surface was observed with Ca treatments. Fruit treated with Ca and any of the inhibitors were less firm than those treated with Ca alone. Specific polyamine biosynthesis inhibitors in combination with Ca may prove useful in reducing postharvest decay in apples.

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Changes in tissue water relations, cell wall calcium (Ca) levels and physical properties of Ca-treated and untreated `Golden Delicious' apples (Malus×domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to 0.34 mol·L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreated fruit. Fruit that were pressure infiltrated with CaCl2 solutions between 0.14 and 0.20 mol·L-1 and then waxed to reduce water loss during storage showed no peel injury. Calcium efflux patterns from apple tissue disks indicated two distinct Ca compartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrations up to 0.20 mol·L-1, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The osmotic potential of apples harvested over three seasons ranged between-1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions up to 0.34 mol·L-1, turgor potential was ≥0.6 MPa in tissue incubated in 0.14 or 0.17 mol·L-1 solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (≤0.03 mol·L-1) or high (≥0.27 mol·L-1) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40% higher in Ca-than in sorbitol-treated tissue. The results suggest that postharvest treatment with 0.14 to 0.20 mol·L-1 solutions of CaCl2 are best for maintaining fruit water relations and storage life of `Golden Delicious' apples while minimizing the risk of salt-related injuries to the fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the risk of fruit injury.

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Effects of postharvest pressure infiltration of distilled water, CaCl2 solutions at 0.14 or 0.27 mol·L-1 without and with subsequent fruit coating treatments of preclimacteric `Golden Delicious' [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Golden Delicious'] apples on volatile levels, respiration, ethylene production, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters; the rest were alcohols, aldehydes, ethers, a ketone, and a sesquiterpene. Pressure infiltration of water and increasing concentrations of CaCl2 resulted progressively in reduced total volatile levels, respiration, ethylene production, and internal O2 levels and increased CO2 levels in fruit following 2 to 4 months storage in air at 0 °C. Total volatile levels, respiration, ethylene production, and internal atmospheres of CaCl2-treated apples at 0.14 mol·L-1 gradually recovered to nontreated control levels following 2 weeks of shelf life at 20 °C and/or storage at 0 °C in air for more than 4 months. Following the calcium treatments with a shellac- or wax-based coating had similar but stronger and more persistent effects on volatile levels, respiration, ethylene production, and internal atmospheres than those found in fruit treated with CaCl2 alone. Calcium infiltration did not change the composition of volatile compounds found in fruit. Results suggest that pressure infiltration of `Golden Delicious' apples with CaCl2 solutions transiently inhibited volatile levels, respiration, and ethylene production, in part, by forming a more-or-less transient barrier to CO2 and O2 exchange between the fruit tissue and the surrounding atmosphere.

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Abstract

The capacity of ‘Eldorado’ pears to ripen increased dramatically after 4 weeks of exposure to 0°C and was associated with the synthesis of ethylene by pear tissue. Endogenous levels of ACC and internal ethylene were low after harvest, but increased rapidly after 4 weeks at 0°. Exposure to 0° for 4 weeks also resulted in an increase in soluble polyuronide during subsequent ripening at 20°. In contrast, after 9 months at 0°, soluble polyuronide content showed little increase when pears were transferred to 20°, and fruit failed to soften normally even though ACC content, internal ethylene concentration, ethylene evolution, and respiration remained relatively high. The content of arabinose, galactose, and rhamnose residues in cell walls decreased substantially during the ripening period after 4 weeks or longer at 0°. These cell wall neutral sugars decreased during ripening, even after 9 months of storage at 0°, while firmness and soluble polyuronide showed little change after fruit were transferred to 20°. These data indicate that the failure of pears to soften normally at 20° after prolonged storage at 0° is not related to ethylene synthesis or to changes in cell wall noncellulosic neutral sugar content, but is probably associated with mechanisms of polyuronide solubilization. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).

Open Access

Abstract

‘Golden Delicious’ apples (Malus domestica Borkh.) were pressure-infiltrated (68.9 kPa) at two harvest dates with 0%, 1%, 2%, or 4% (w/v) solutions of CaCl2 and stored at 0C for 2, 4, or 6 months followed by 1 week at 20C. Calcium concentrations, axial compression profiles, and Magness-Taylor firmness were measured. Calcium chloride infiltration increased all measures of tissue strength immediately and relative increases persisted during storage. A 1-week difference in harvest date markedly affected Ca uptake and textural responses; however, for both dates, 2% CaCl2 was effective in firming the apples. Apples from the second harvest, which were treated with 2% CaCl2 and stored for 6 months, had textural measurement values equal to or greater than those of comparable apples infiltrated only with water and measured before storage. Calcium chloride at 4% had a greater firming effect, but caused severe surface damage. Differential reponses to CaCl2 levels and storage durations by various textural measurements indicate that supplemental Ca not only increased firmness retention during storage, but also induced patterns of textural change different from those that occurred under the influence of the endogenous Ca alone.

Open Access

The effects of postharvest pressure infiltration of calcium chloride (CaCl2) solutions, fruit coatings and shrink-wrap film treatments of apples (Malus domestica Borkh. `Golden Delicious') on peel injury, quality attributes, respiration and internal atmospheres after storage at 0 °C for 2 to 6 months, and during subsequent ripening at 20 °C were investigated. CaCl2 treatments (0.14 to 0.34 mol·L-1) reduced internal and evolved ethylene and softening of fruits, but they also caused distinctive injury to the fruit surface. Following the CaCl2 treatments with a water rinse and a wax- or shellac-based coating or a shrink-wrap film reduced surface injury in fruits treated with 0.24 or 0.34 mol·L-1 solutions of CaCl2 and eliminated injury resulting from a 0.14 mol·L-1 CaCl2 treatment. The fruit coatings delayed ripening; as indicated by better retention of fresh mass, green peel color, titratable acidity and flesh firmness, and the reduced respiration and ethylene production rates that were observed upon transferring the fruits to 20 °C. Sequential treatments with CaCl2 and a shrink-wrap film also reduced fresh mass loss, respiration and ethylene production rates, but had no effect on other quality characteristics. Internal CO2 levels increased and O2 and ethylene levels decreased in surface coated fruits during storage at 0 °C. Coating fruits without the use of CaCl2 also delayed ripening though not as well as that for fruits sequentially treated with CaCl2 and a surface coating.

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Allyl isothiocyanate (AITC) is the predominant isothiocyanate produced by damaged tissues of Indian mustard (Brassica juncea (L) Czerniak). This study investigated Indian mustard and AITC mediated suppression of mycelial growth and sclerotial germination of Sclerotium rolfsii Saccardo, a common soilborne pathogen. Indian mustard (IM) treatments of 0, 0.1, 0.2, 0.6, 1.0, 2.0, 4.1, 5.1, 10.2, 20.4, 40.8, 81.6, and 163.3 g·L-1 (weight of reconstituted mustard per liter of air) were evaluated for suppression of mycelial growth. Treatment effect was evaluated by measuring the radial growth of mycelia. Sclerotia were placed in culture tubes containing 18 g autoclaved soil and covered with an additional 5 g soil. AITC at concentrations of 0, 4.0, 16.0, 64.0, 256.0, 1024.0, or 4096.0 μmol·L-1 was injected into the tubes. Treated sclerotia were removed from tubes and plated on potato dextrose agar to determine viability. Mycelial growth was inhibited with IM treatments (P < 0.01). Inhibiting concentrations (IC) of IM for mycelial growth inhibition of 50% and 90% were 0.7 and 1.0 g·L-1, respectively, with death resulting with >2 g·L-1. Inhibition attributable to AITC alone was lower than that achieved by IM producing equivalent amounts of AITC. Germination of sclerotia was negatively correlated with AITC concentration (r = 0.96; P < 0.01). The IC50 and IC90, of AITC were 249.0 and 528.8 μmol·L-1, respectively, at 42 hours. The lethal concentration for sclerotia was not reached; only suppression occurred at the highest treatment concentrations. Sclerotium rolfsii mycelia were sensitive to the IM volatiles and were suppressed at low concentrations. Sclerotia were more resistant than the mycelia and required higher concentrations of AITC to suppress germination.

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