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Glenn J. Stadelbacher and Krishna Prasad

Abstract

Decay of apples (Malus sylvestris Mill.) inoculated with Penicillium expansum was controlled by acetaldehyde vapor concentrations (v/v) of 0.5% for 180 min, 1% for 120 min, 2% for 60 min, and 3% for 30 min. The above treatments did not produce lenticel or skin injury. Fumigated conidia did not germinate in 21 days at 21°C on artificial media and failed to induce decay in stem-punctured apples. The pathogen could not be re-isolated from fumigated inoculated punctures, however, the pathogen was obtained from inoculated punctures not exposed to acetaldehyde vapor. Fungicidal action of acetaldehyde vapor was a function of concentration and exposure period. Objectional off-flavors were not detected in fumigated apples, although appreciable amounts of acetaldehyde vapor were absorbed.

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S.-S.T. Hua, J.L. Baker, and M. Flores-Espiritu

California is the major state for producing almonds, pistachios, and walnuts, with a total market value of $1.6 billion. Both domestic and export markets of these nuts presently allow a maximum level of aflatoxin B1 contamination in the edible nuts to be 20 ppb. Even very low degrees of infection of the nuts by A. flavus can result in aflatoxin levels above the mandatory standards. Biological control to reduce the population of and to inhibit the biosynthesis of A. flavus in orchards may be useful to decrease infection and thus aflatoxin content in the edible nuts. Certain saprophytic yeasts were shown to effectively compete with postharvest fungal pathogens such as Penicillium expansum and Botrytis cinerea. The potential of saprophytic yeasts to reduce aflatoxin contamination in tree nuts has not been hitherto extensively explored. A safe visual bioassay for screening yeasts antagonistic to A. flavus has been developed. The nor mutant of A. flavus has a defective norsolorinic acid reductase and blocks the aflatoxin biosynthetic pathway, resulting in the accumulation of norsolorinic acid, a bright red-orange pigment. We used the nor mutant in the assay to screen yeasts strains for their ability to inhibit aflatoxin production by visually scoring the accumulation of this pigment as well as the growth and sporulation of the fungus. Yeast strains that reduced the red-orange pigment accumulation in the nor mutant were identified and shown to inhibit aflatoxin biosynthesis of several toxigenic strains of A. flavus.

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Altaf Qadir and Fumio Hashinaga

Nitrous oxide (N2O) was tested as a potential fungicidal or fungistatic compound. Twelve postharvest fungi were exposed to 10 to 80 kPa with 20 kPa O2 in a static system at 20 °C. These fungi were divided into N2O high-, medium- and low-sensitive groups. Based on growth sensitivity, growth of high-sensitive fungi was completely inhibited, and that of medium-sensitive fungi up to 85%. With low-sensitive fungi, significant inhibition was achieved only when the fungi were exposed to N2O continuously for 6 days. Botrytis cinerea Pers.: Fr., Colletotrichum acutatum Simmonds, Monilinia fructicola (Winter) Honey, Penicillium expansum Link, Penicillium italicum Wehmer, Phytophthora citrophthora (R.E. Smith and E.H. Smith) Leonian and Rhizopus stolonifer (Ehrens.: Fr.) Vuillemin, were high-sensitive; Glomerella cingulata (Stoneman) Spaulding was medium-sensitive, and Alternaria alternata (Fr.) Keissler, Fusarium oxysporum Schlechtend1: Fr. f. sp. fragariae Winks and Williams, Fusarium oxysporum Schlechtend1: Fr. f. sp. lycopersici (Saccardo) Snyder and Hansen., and Geotrichum candidum Link., were low-sensitive fungi. Addition of up to 100 μL·L-l C2H4 did not reduce inhibition caused by N2O. The inhibitory effect of N2O was considered to be due to biophysical properties similar to CO2, the competitive inhibition on C2H4 action, or the biosynthesis of methionine. These results indicate the potential of N2O to control some postharvest decay fungi.

Open access

R. E. Hardenburg and D. H. Spalding

Abstract

Benomyl and thiabendazole (TBZ), at concn of 1,000 ppm, were compatible with commercial scald inhibitors (2,700 ppm ethoxyquin or 2,000 ppm diphenylamine). No injury was observed on ‘ Delicious’ or ‘Stayman’ apples given combined treatments and stored 5 months at 0°C plus 6 or 7 days at 21°C. Effectiveness of fungicide and scald inhibitor was not altered when combined.

Both benomyl and TBZ used as 10-15 sec dip treatments at 500 ppm controlled decay due to blue mold (Penicillium expansum) and gray mold (Botrytis cinerea) at puncture wounds in inoculated apples. They were less effective in controlling decay at bruises unless suspensions were heated in a range of 29°-45°C (84°-l 13°F) and used as a 2-min dip. Unheated benomyl was more effective than unheated TBZ in reducing blue mold at bruises. TBZ was less effective in controlling decay at punctures when treatment was delayed 24 hr after inoculation. TBZ added to water contaminated with blue mold spores, as in a dump tank, controlled decay at skin punctures but not at bruises during subsequent storage. Neither benomyl nor TBZ controlled Alternaria rot, which often developed at punctures when blue and gray mold rot were controlled.

Open access

R. E. Hardenburg and R. E. Anderson

Abstract

‘Stayman’ apples (Malus domestica Borkh.) dipped in 4% CaC12 were firmer after 5–6 months storage in air at 0°C and developed less senescent breakdown than untreated fruit. Use of the thickener Keltrol with CaC12 or vacuum infiltrating (VI) CaC12 resulted in the firmest fruit after storage and the highest flesh Ca levels. ‘Stayman’ stored 5 or 6 months in CA at 0°C were 1.5 kg firmer than air-stored fruit. Dipping apples in CaC12 prior to CA storage provided little additional benefit. Liquid concentrate formulations of diphenylamine (DPA) and ethoxyquin used alone or in combination with 4% CaC12 gave excellent scald control on ‘Stayman’ stored 5 or 6 months at 0° + 6 days at 20°. However, the same chemicals gave poor scald control for ‘Starkrimson Delicious’ picked early to midseason. The antioxidants BHT and BHA evaluated as postharvest dips at 2,000 ppm were less effective than DPA or ethoxyquin in controlling scald on ‘Stayman’. ‘Delicious’ apples were not significantly firmer after 6 months storage in air at 0°C when dipped in 3% CaC12 alone or with Keltrol, or when CaC12 was VI. When CaC12 was contaminated with Penicillium expansum spores, VI of the solution greatly increased decay of both ‘Delicious’ and ‘Stayman’.

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Ali A. Ramin, P. Gordon Braun, Robert K. Prange, and John M. DeLong

Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.

Free access

Jun Song, Rujida Leepipattanawit, Weimin Deng, and Randolph M. Beaudry

Hexanal vapor inhibited hyphae growth of Penicillium expansum and Botrytis cinerea on potato dextrose agar (PDA) and on apple (Malus domestica Borkh.) slices. After 48 hours exposure to 4.1 μmol·L-1 (100 ppm) hexanal, the hyphae growth of both fungi was about 50% that of untreated controls. At a concentration of 10.3 μmol·L-1 (250 ppm), neither fungus grew during the treatment period, however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of 18.6 μmol·L-1 (450 ppm) or more, the growth of both fungi ceased and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 10.3 μmol·L-1 hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 18.6 μmol·L-1 stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on `Golden Delicious' and on `Jonagold' apple slices. Hexanal was actively converted to aroma volatiles in `Jonagold' and `Golden Delicious' apple slices, with hexanol and hexylacetate production strongly enhanced after 20 to 30 hours treatment. A small amount of butylhexanoate and hexylhexanoate production was also noted. Within 16 hours after treatment, no hexanal could be detected emanating from treated fruit. Since hexanal was metabolized to aroma-related volatiles by the fruit slices, the possibility of hexanal being an essentially residue-less antifungal agent seems likely. The possibility of developing a system for treating apple slices with hexanal in modified-atmosphere packages was also examined. The permeability of low-density polyethylene (LDPE) film to hexanal and hexylacetate was, respectively, about 500- and 1000-fold higher than LDPE permeability to O2. The permeability of both compounds increased exponentially with temperature, with hexanal permeability increased 6-fold while hexylacetate increased only 2.5-fold between 0 and 30 °C.

Open access

R. F. Lee, L. W. Timmer, and L. G. Albrigo

Abstract

Citrus blight is a vascular wilt disease of unknown etiology. Blight-affected ‘Pineapple’ sweet orange [Citrus sinensis (L.) Osb.] trees on rough lemon (C. jambhiri Lush.) rootstock in early stages of decline were treated with benzimidazole fungicides or with oxytetracycline (OTC) by trunk injection, soil drench, or injection plus drench. The distribution and persistence of the materials were monitored by bioassay using Bacillus cereus var. mycoides for OTC and Penicillium expansum L. for benzimidazoles. Both materials were well-distributed in the canopy following trunk injections, in the root systems following soil drenches, and though most of the tree after injection plus drench treatments. Benzimidazoles and OTC persisted within the trees for several months and relatively high levels of activity were maintained for over a year by 3 applications. OTC persisted in soil for more than 6 months; whereas, benomyl disappeared from the soil in 3 months or less. Although high levels of bactericidal or fungicidal activity were maintained in the treated trees, most treated trees declined as rapidly as the untreated control trees. The injection plus drench group treated with OTC showed a slight improvement after 2 years. None of the treatments increased tree growth or resulted in increased water uptake. High levels of zinc in trunk wood, an internal symptom of blight, were unaffected by the benzimidazole treatments, but injection plus drench treatment with OTC significantly reduced zinc levels in trunk wood. Since neither OTC nor benzimidazoles completely reversed symptoms of blight, we were unable to conclusively confirm or refute proposed bacterial or fungal etiologies for citrus blight.

Free access

Robert A. Saftner, Judith A. Abbott, William S. Conway, and Cynthia L. Barden

Prestorage heat, CA storage, and pre- and poststorage treatments with the ethylene action inhibitor, 1-methylcyclopropene (MCP), were tested for their efficacy at inhibiting fungal decay and maintaining quality in `Golden Delicious' apples [Malus sylvestris (L.) Mill. Yellow Delicious Group] stored 0 to 5 months at 0 °C and 7 days at 20 °C. Before storage in air at 0 °C, preclimacteric fruit were treated with either MCP at a concentration of 1 μL·L-1 for 17 hours at 20 °C, 38 °C air for 4 days, MCP plus heat, or left untreated. Some sets of untreated fruit were stored in a controlled atmosphere of 1.5 kPa O2 and 2.5 kPa CO2 at 0 °C while other sets were removed from cold storage in air after 2.5 or 5 months, warmed to 20 °C, and treated with 1 μL·L-1 MCP for 17 hours. Prestorage MCP, heat, MCP plus heat treatments and CA storage decreased decay severity caused by wound-inoculated Penicillium expansum Link, Botrytis cinerea Pers.:Fr., and Colletotrichum acutatum Simmonds (teleomorph Glomerella acutata J.C. Guerber & J.C. Correll sp.nov.). Poststorage MCP treatment had no effect on decay severity. Both prestorage MCP treatment and CA storage delayed ripening as indicated by better retention of green peel color, titratable acidity, and Magness-Taylor flesh firmness, and the reduced respiration, ethylene production rates, and volatile levels that were observed upon transferring the fruit to 20 °C. The prestorage MCP treatment delayed ripening more than CA storage. Following 5 months cold storage, the prestorage MCP treatment maintained the shape of the compression force/deformation curve compared with that of fruit at harvest, as did CA storage, but at a lower force profile. The heat treatment had mixed effects on ripening: it hastened loss of green peel color and titratable acidity, but maintained firmness and delayed increases in respiration, ethylene production and volatile levels following cold storage. The MCP plus heat treatment inhibited ripening more than heat treatment alone but less than MCP treatment alone. In one of 2 years, the MCP plus heat treatment resulted in superficial injury to some of the fruit. Results indicated that MCP may provide an effective alternative to CA for reducing decay severity and maintaining quality during postharvest storage of `Golden Delicious' apples. Prestorage heat to control decay and maintain quality of apples needs further study, especially if used in combination with MCP.

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Jennifer R. DeEll, Jennifer T. Ayres, and Dennis P. Murr

1-MCP had no significant effect on the incidence. Errampalli et al. (2004 , 2005) found 1-MCP to have variable effects on postharvest blue mold ( Penicillium expansum ) and gray mold ( Botrytis cinerea ) in apples, including ‘Empire’ and