Joseph L. Smilanick

Effects of continuous 0.3 ppm ozone exposure on decay development and physiological responses of peaches and table grapes in cold storage

Continuous ozone exposure at 0.3 ppm (v/v) (US-OSHA Threshold Limit Value for short term exposure) inhibited aerial mycelial growth and sporulation on ‘Elegant Lady’ peaches wound inoculated with Monilinia fructicola, Botrytis cinerea, Mucor piriformis ,o rPenicillium expansum and stored for 4 weeks at 5 °C and 90% relative humidity (RH). Aerial growth and sporulation, however, resumed afterward in ambient atmospheres. Ozone exposure did not significantly reduce the incidence and severity of decay caused by these fungi with the exception of brown rot. Gray mold nesting among ‘Thompson Seedless’ table grapes was completely inhibited under 0.3 ppm ozone when fruit were stored for 7 weeks at 5 °C. Gray mold incidence, however, was not significantly reduced in spray inoculated fruit. Continuous ozone exposure at 0.3 ppm increased water loss after 5 weeks of storage at 5 °C and 90% RH in ‘Zee Lady’ peaches but not after 4 weeks of storage in ‘Flame Seedless’ grapes. Respiration and ethylene production rates of ‘O’Henry’ peaches were not affected by previous exposure to 0.3 ppm ozone. In every test, no phytotoxic injuries of fruit tissues were observed in ozonated or ambient atmosphere treatments.

Enhancement of the performance of Candida saitoana by the addition of glycolchitosan for the control of postharvest decay of apple and citrus fruit

At a concentration of 0.025% (w/v) chitosan-chloride inhibited spore germination of Botrytis cinerea, Penicillium expansum, and Candida saitoana. In contrast, at 0.5% (w/v) glycolchitosan inhibited spore germination of B. cinerea and P. expansum, but not the growth of C. saitoana in vitro or in apple wounds. The combination of C. saitoana with 0.2% glycolchitosan was more effective in controlling gray and blue mold of apple caused by B. cinerea and P. expansum, respectively, and green mold of oranges and lemons caused by P. digitatum than C. saitoana or 0.2% glycolchitosan alone. The level of control was similar to that obtained with the fungicide imazalil on oranges and lemons. C. saitoana in combination with 0.2% glycolchitosan reduced green mold incidence equally on light green and yellow lemons, while C. saitoana was more effective on light green lemons than on yellow lemons. When applied as a pretreatment, sodium carbonate enhanced the efficacy of all treatments tested against green mold with the greatest effect on light green lemons. Of the treatments tested, pretreatment with sodium carbonate followed by the combination of C. saitoana with 0.2% glycolchitosan was the most effective in controlling green mold of both light green and yellow lemons.

Combination of Hot Water and Ethanol to Control Postharvest Decay of Peaches and Nectarines

Spores of Monilinia fructicola or Rhizopus stolonifer were immersed in water or 10% ethanol (EtOH) for 1, 2, 4, or 8 min at temperatures of 46 or 50°C to determine exposure times that would produce 95% lethality (LT95). EtOH reduced the LT95 by about 90%. Peaches and nectarines infected with M. fructicola were immersed in hot water alone or with EtOH to control decay. EtOH significantly increased the control of brown rot compared to water alone. Immersion of fruit in water at 46 or 50°C for 2.5 min reduced the incidence of decayed fruit from 82.8% to 59.3 and 38.8%, respectively. Immersion of fruit in 10% ethanol at 46 or 50°C for 2.5 min further reduced decay to 33.8 and 24.5%, respectively. Decay after triforine (1,000 μg ml-1) treatment was 32.8%. Two treatments, 10% EtOH at 50°C for 2.5 min and 20% EtOH at 46°C for 1.25 min, were selected for extensive evaluation. The flesh of EtOH-treated fruit was significantly firmer, approximately 4.4 N force, than that of control fruit among seven of nine cultivars evaluated. No other factor evaluated was significantly influenced by heated EtOH treatments. The EtOH content of fruit treated with 10 or 20% EtOH was approximately 520 and 100 μg g-1 1 day and 14 days after treatment, respectively.

Application of Candida saitoana and glycolchitosan for the control of postharvest diseases of apple and citrus fruit under semi-commercial conditions

The efficacy of the combination of Candida saitoana with 0.2% glycolchitosan (the bioactive coating) as a biocontrol treatment of postharvest diseases of apple and citrus fruit was evaluated in tests with natural inoculations that simulated commercial packinghouse conditions. The growth of C. saitoana in apple wounds and on fruit surfaces was not affected by glycolchitosan. The bioactive coating was more effective in controlling decay of several cultivars of apples (Red Delicious, Rome, Golden Delicious, and Empire) than either C. saitoana or 0.2% glycolchitosan alone. Depending on the apple cultivar used, the bioactive coating was comparable or superior to thiabendazole in reducing decay. The bioactive coating was also superior to C. saitoana in controlling decay of oranges (cvs. Washington navel, Valencia, Pineapple, and Hamlin) and cv. Eureka lemons, and the control level was equivalent to that with imazalil. The bioactive coating and imazalil treatments offered consistent control of decay on Washington navel oranges and Eureka lemons in early and late seasons, while C. saitoana or 0.2% glycolchitosan were most effective on early-season fruit. The combination of C. saitoana with 0.2% glycolchitosan also reduced the incidence of stem-end rot of cv. Valencia oranges, but control was less effective than treatment with imazalil.

Influence of pH and NaHCO3 on Effectiveness of Imazalil to Inhibit Germination of Penicillium digitatum and to Control Postharvest Green Mold on Citrus Fruit

In vitro, spores of Penicillium digitatum germinated without inhibition between pH 4 and 7, but were inhibited at higher pH. Estimated concentrations of imazalil (IMZ) in potato-dextrose broth-Tris that caused 50% reduction in the germination of spores (ED50) of an IMZ-sensitive isolate M6R at pH 4, 5, 6, and 7 were 0.16, 0.11, 0.015, and 0.006 μg/ml, respectively. ED50 IMZ concentrations of an IMZ-resistant isolate D201 at pH 4, 5, 6, and 7 were 5.9, 1.4, 0.26, and 0.07 μg/ml, respectively. The natural pH within 2-mm-deep wounds on lemon was 5.6 to 5.1 and decreased with fruit age. IMZ effectiveness to control green mold and its residues increased with pH. The pH in wounds on lemon fruit 24 h after immersion in 1, 2, or 3% NaHCO3 increased from pH 5.3 to 6.0, 6.3, and 6.7, respectively. NaHCO3 dramatically improved IMZ performance. Green mold incidence among lemon fruit inoculated with M6R and treated 24 h later with IMZ at 10 μg/ml, 1% NaHCO3, or their combination was 92, 55, and 22%, respectively. Green mold among lemon fruit inoculated with D201 and treated 24 h later with water, IMZ at 500 μg/ml, 3% NaHCO3, or their combination was 96.3, 63.0, 44.4, and 6.5%, respectively. NaHCO3 did not influence IMZ fruit residue levels.

Near-Harvest Applications of Metschnikowia fructicola, Ethanol, and Sodium Bicarbonate to Control Postharvest Diseases of Grape in Central California

The yeast Metschnikowia fructicola, ethanol, and sodium bicarbonate (SBC), alone or in combinations, were applied to table grapes on vines 24 h before harvest to control the incidence of postharvest diseases. In four experiments, all significantly reduced the total number of decayed berries caused by Botrytis cinerea, Alternaria spp., or Aspergillus niger after storage for 30 days at 1°C followed by 2 days at 20°C. In three experiments, a mean gray mold incidence (caused by B. cinerea) of 34.2 infected berries per kilogram among untreated grape was reduced by Metschnikowia fructicola at 2 × 107 CFU/ml, ethanol at 50% (vol/vol), or SBC at 2% (wt/vol) to 12.9, 8.1, or 10.6 infected berries per kilogram, respectively. Ethanol, SBC, and SO2 generator pads were similarly effective. M. fructicola effectiveness was not improved when combined with ethanol or SBC treatments. Ethanol and yeast treatments did not harm the appearance of the grapes. M. fructicola and SBC left noticeable residues, and SBC caused some visible phytotoxicity to the rachis and berries. Ethanol applied at 50% (vol/vol) reduced epiphytic fungal and bacterial populations by about 50% compared with controls. M. fructicola populations persisted on berries during storage when applied alone or after ethanol treatments, whereas SBC reduced its population significantly.

Effect of Gaseous Ozone Exposure on the Development of Green and Blue Molds on Cold Stored Citrus Fruit

The effects of gaseous ozone exposure on in vitro growth of Penicillium digitatum and Penicillium italicum and development of postharvest green and blue molds on artificially inoculated citrus fruit were evaluated. Valencia oranges were continuously exposed to 0.3 ± 0.05 ppm(vol/vol) ozone at 5°C for 4 weeks. Eureka lemons were exposed to an intermittent day-night ozone cycle (0.3 ± 0.01 ppm ozone only at night) in a commercial cold storage room at 4.5°C for 9 weeks. Both oranges and lemons were continuously exposed to 1.0 ± 0.05 ppm ozone at 10°C in an export container for 2 weeks. Exposure to ozone did not reduce final incidence of green or blue mold, although incidence of both diseases was delayed about 1 week and infections developed more slowly under ozone. Sporulation was prevented or reduced by gaseous ozone without noticeable ozone phytotoxicity to the fruit. A synergistic effect between ozone exposure and low temperature was observed for prevention of sporulation. The proliferation of spores of fungicide-resistant strains of these pathogens, which often develop during storage, may be delayed, presumably prolonging the useful life of postharvest fungicides. In vitro radial growth of P. italicum, but not of P. digitatum, during a 5-day incubation period at 20°C was significantly reduced by a previous 0.3 ± 0.05 ppm ozone exposure at 5°C for 4 days. Inoculum density did not influence the effect of gaseous ozone on decay incidence or severity on oranges exposed to 0.3 ± 0.05 ppm ozone at 20°C for 1 week. Susceptibility of oranges to decay was not affected by a previous continuous exposure to 0.3 ± 0.05 ppm ozone at 20°C for 1 week. A corona discharge ozone generator was effective in abating ethylene in an empty export container.

Improved Control of Apple and Citrus Fruit Decay with a Combination of Candida saitoana and 2-Deoxy-D-Glucose

A combination of Candida saitoana with 0.2% 2-deoxy-D-glucose to control decay of apple, lemon, and orange fruit was evaluated. Growth of C. saitoana in vitro was reduced by 2-deoxy-D-glucose; however, in apple wounds, the yeast grew as well in the presence of 2-deoxy-D-glucose as in its absence. When applied to fruit wounds before inoculation, the combination of C. saitoana with 0.2% 2-deoxy-D-glucose was more effective in controlling decay of apple, orange, and lemon caused by Botrytis cinerea, Penicillium expansum, and P. digitatum than either C. saitoana or the application of a 0.2% solution of 2-deoxy-D-glucose alone. Increasing the concentration of 2-deoxy-D-glucose from 0.2 to 0.5% did not improve control significantly. The combination of C. saitoana with 0.2% 2-deoxy-D-glucose was also effective against infections established up to 24 h before treatment. When applied within 24 h after inoculation, the combination of C. saitoana with 0.2% 2-deoxy-D-glucose was very effective in controlling blue mold of apple and green mold of orange and lemon. The level of control of green mold was equivalent to imazalil treatment. When either C. saitoana or 0.2% 2-deoxy-D-glucose was applied within 24 h after inoculation, neither had an effect on disease development on apple, orange, or lemon, and the incidence of decay was similar to the water-treated control.

Control of postharvest brown rot of nectarines and peaches by Pseudomonas species.

Abstract Microbes were applied to nectarines and peaches to control postharvest brown rot caused by Monilinia fructicola. Two yeasts applied to wounds on fruit before inoculation protected fruit from subsequent infection, but they could not control decay when applied after inoculation. Two antibiotic-producing bacteria, Pseudomonas corrugata and P. cepacia, significantly reduced decay when applied up to 12 h after inoculation. P. corrugata controlled decay with fewer colony-forming units (c.f.u.) than P. cepacia;

Preharvest Chitosan and Postharvest UV Irradiation Treatments Suppress Gray Mold of Table Grapes

The effectiveness of chitosan treatment of table grapes, alone or in combination with ultraviolet-C (UV-C) radiation, to control postharvest gray mold caused by Botrytis cinerea, was determined in California, United States. The influence of these treatments on catechin and resveratrol contents and chitinase activity in grape berry skins also was assessed. Clusters of cvs. Thompson Seedless, Autumn Black, and Emperor were sprayed in the vineyard with 1% chitosan, then harvested daily for 5 days. Promptly after harvest, they were inoculated with B. cinerea. Decay incidence and disease severity were significantly reduced by chitosan, which was most effective on berries harvested 1 or 2 days after treatment. In another experiment, grape berries were sprayed in the vineyard with chitosan, harvested 2 days later, irradiated for 5 min with UV-C (0.36 J/cm2), and inoculated with B. cinerea 2 days later. Combined chitosan and UV-C treatments applied to cv. Autumn Black or selection B36-55 were synergistic in reducing gray mold incidence and severity compared with either treatment alone. Preharvest chitosan treatment increased neither concentration of catechin or resveratrol nor activity of chitinase in berry skin. Conversely, UV-C irradiation, alone or combined with chitosan treatment, induced catechin in cv. Autumn Black berries and trans-resveratrol in both cv. Autumn Black and selection B36-55.