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When the fungus Fusarium tricinctum NRRL 3299 was grown under atmospheres enriched with 50% CO2 and above (given in combination with 20% O2), T-2 production was reduced to 4.0 μg/45 ml of medium, as compared with 21.2 μg/45 ml of medium produced in an atmosphere of air. At 60% CO2/20% O2 and 80% CO2/20% O2, a significant reduction in fungal growth was also observed. The possibility of using controlled atmospheres as a means for mycotoxin control is discussed.

This chapter focuses on sprout inhibition by irradiation of potato tubers, onion and garlic bulbs, and carrot roots. Factors affecting sprout inhibition and postirradiation changes in these subterranean organs were described.

Phytosanitary treatments such as irradiation disinfest host commodities of quarantine insect pests before they are exported to areas where the pests do not occur and are often the simplest approach to overcome regulatory trade barriers and gain market access. Irradiation is a versatile technology to disinfest fresh and durable agricultural commodities of quarantine pests. Irradiation is broadly effective against insects and mites, cost competitive with other disinfestation methods such as chemical fumigation, and fast. Irradiation generally does not significantly reduce commodity quality at the doses used to control insect pests and may extend shelf life. Additionally, irradiation can be applied to the commodity after packaging. Research methods for developing irradiation treatments for insect disinfestation and the history of developing regulations for phytosanitary irradiation are discussed.

Response of fungal cells to inactivation by ionizing radiation is governed by several factors of which the inherent resistance is the first. Factors affecting the sensitivity to irradiation of postharvest fruits and vegetables and their enzymatic activity have been reviewed. This chapter focuses on the suppressive effects of irradiation on decay development. The impact of irradiation alone or combined with other postharvest techniques on decay suppression and on the ripening process of fruits was discussed.

Several issues present barriers to the wider use of phytosanitary irradiation. Because irradiation is characterized as a food additive rather than a process, its use must be disclosed on a label. The labeling requirement may be a drawback for retailers who believe consumers are reluctant to buy irradiated food. The 1-kGy limit is archaic and reduces the efficiency of applying the treatment. The United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) has placed limits on the use of modified atmosphere packaging with irradiation, which disrupts commercial practices that ensure superior commodity quality. The limited number of countries that have approved phytosanitary uses of irradiation is hampering broader adoption because of closed markets.

The first chapter focuses on the purposes of applying ionizing radiation to fruits and vegetables. These include the extension of their useful shelf life by inactivating postharvest pathogens or/and by delaying ripening and senescence, and inhibiting sprouting of tubers, bulbs, and roots of subterranean vegetables. Most important purposes are the improvement of microbial safety associated with human pathogenic bacteria contaminating the fresh produce and providing relevant data on wholesomeness and safety of irradiated food. Chemical and nutritional changes occurring after irradiation should be provided.

Increased consumption of fresh-cut fruits and vegetables raised the concern about microbial safety because they serve as suitable growth media for human pathogenic bacteria associated with outbreaks of food-borne diseases. Recent studies evaluated the ability of irradiation combined with modified-atmosphere packaging (produced around fresh-cut produce) indicated that this combination was capable of eliminating or reducing the contaminating human bacteria and enhancing microbial quality with reduced irradiation doses. It was generally found that fresh and fresh-cut fruits and vegetables can tolerate low irradiation doses of up to 1 kGy, without causing significant changes in the quality of the produce. The fresh-cut fruits reviewed were mangoes, papayas, guavas, apples, and blueberries, and the fresh-cut vegetables reviewed were tomatoes, bell peppers, eggplants, cucumbers, melons, broccoli, celery, lettuce, watercress, spinach leaves, endive, green onions, carrots, potatoes, beets, and mushrooms.

This chapter discusses the radiation effects on mycotoxins in infected fruits and vegetables, including patulin, aflatoxins, ochratoxin, and Alternaria mycotoxins. The best way to reduce mycotoxin level is to eliminate the appearance of toxin-producing fungi at preharvest, during harvest, or mainly at postharvest stages.

This chapter reviews the postirradiation changes in fruits and vegetables, including microbiological changes, changes in quality parameters, nutritional changes (vitamin C content), and chemical changes, including antioxidant capacity, phenolic compounds, and enzymatic changes.

This chapter reviews the effects of radiation alone or combined with other postharvest treatments on quality parameters of fruits, including citrus fruits, avocados, mangoes, papayas, bananas, pineapples, litchis, persimmons, guavas, annona fruits, pomegranates, dates, figs, pome and stone fruits, strawberries, raspberries, blueberries, blackberries, and kiwifruits. Review on each fruit is accompanied by the beneficial effects of irradiation versus the adverse effects. To allow the use of radiation doses beneath those inducing peel damage, the combination of low doses with other postharvest techniques, acting synergistically or additively, were used. These included heating, modified or controlled atmosphere, modified-atmosphere packaging, various coatings and polymeric film wrapping, chemical application, heated chemicals, cold storage, and others.

This chapter reviews the effects of radiation alone or combined with other postharvest techniques on shelf life and quality parameters of vegetables. The vegetables included are tomatoes, bell peppers, melons, lettuce, cilantro, cabbage, broccoli, carrots, potatoes, onions, garlic, and mushrooms. Each review is accompanied by beneficial effects of irradiation versus the adverse effects. The combined techniques included heat radiation, heat–chemical radiation, irradiation and modified-atmosphere packaging, irradiation with refrigeration, and wrapping materials.

Studies carried out for more than six decades clarified that ionizing radiation can serve as alternative physical means for shelf life extension of fresh produce, decay control, retardation of fruit ripening and senescence processes, maintenance of wholesomeness, enhancement of microbial safety, and sprout inhibition of subterranean vegetables. Irradiation has also been associated with maintenance or enhancement of antioxidant activity. Comparison of irradiation with other preservation techniques of fresh produce clarified its advantages. However, the acceptance of irradiation as a means for preservation of fresh produce and microbial safety has generally met with public opposition because of economic and logistic factors or psychological problems. Attention has been given to the need of sensitive and reliable analytical techniques to identify irradiated food.

In 2006, US Department of Agriculture Animal and Plant Health Inspection Service published a landmark rule providing generic radiation quarantine treatments. The rule approved radiation doses of 150 Gy for any tephritid fruit fly and 400 Gy for all other insects except the pupa and adult stages of Lepidoptera. The generic radiation treatments apply to all fresh horticultural commodities. Therefore, if a pest risk assessment demonstrates that no pupae or adult Lepidoptera are associated with a commodity, export approval can be forthcoming with no further research. Generic treatments are the culmination of decades of research but not an end point. Future research on quarantine and phytosanitary uses of radiation should focus on (1) development of specific doses for quarantine Lepidoptera not covered by the generic treatments, (2) reduction of dose levels for specific pests and commodities to shorten treatment time and minimize any deleterious effects of radiation treatment on commodity quality, (3) development of generic doses below 400 Gy for important groups of quarantine arthropods other than fruit flies, and (4) development of information on commodity tolerance and development of value-added irradiated fresh products using generic radiation treatments. Generic treatments will facilitate safe trade between countries that have approved phytosanitary uses of radiation for fresh agricultural commodities.

The antifungal activity of Aloe vera gel at 1–105 μl l−1 was tested on four common postharvest fruit pathogens: Penicillium digitatum, P. expansum, Botrytis cinerea, and Alternaria alternata. The natural gel suppressed both germination and mycelial growth with P. digitatum and A. alternata being the most sensitive species. Spore survival of P. digitatum, A. alternata, and B. cinerea was reduced by 15–20% at 1 μl l−1, but the gel was similarly effective against P. expansum only when the concentration exceeded 103 μl l−1. For the first two species, the suppressive effect of the gel increased with an increase in the concentration, culminating in 95% reduction in spore survival at 105 μl l−1. B. cinerea, however, responded with a partial germination recovery when the gel concentration was greater than 10 μl l−1. The inhibitory effect of the plant gel on colony growth was exhibited at 1 μl l−1, when a 67–69% reduction in radial growth was recorded for P. digitatum, A. alternata, and B. cinerea, and a 19% reduction for P. expansum after five days on potato dextrose agar (PDA) at 23 °C. The effect of the gel on disease development in P. Digitatum-inoculated grapefruit was expressed by both a delay in lesion development and a significant reduction in the incidence of infection following dipping in a concentration of plant gel of 103 μl l−1.

A combined TBZ — iprodione treatment was more effective in inhibiting growthin vitro ofBotrytis cinerea isolates obtained from decayed celery than either of the fungicides applied separately. This was exhibited for both TBZ-resistant and TBZ-sensitive isolates. TBZ at 500 (μg ml-1 plus iprodione at 1000 μg ml-1 reduced celery decay beyond the reduction obtained by each fungicide alone. When applied prior to inoculation, the combined treatment prevented decay by the TBZ-sensitive/iprodione-resistant isolates and reduced initial decay by the TBZ-resistant/iprodione-sensitive isolates to 3–10% of the level without treatment. Under natural infection conditions iprodione showed better decay control than TBZ, and at 1500 μg ml-1 it reduced initial decay during prolonged storage to 3% of the no-treatment level. Although TBZ (500 μg ml-1) or iprodione (1000 μg ml-1) applied separately reduced decay significantly, the combination of lower concentrations of each fungicide was sufficient to eliminate decay development almost totally. The combined treatment also inhibited decay bySclerotinia sclerotiorum, which contributed 3% of the total soft rot in stored celery.

A hot water dip at 50°C for 2 min was more effective than 1 KGy of gamma radiation in reducing Botrytis cinerea and Rhizopus stolonifer decay in inoculated light-red tomatoes. The combined hot water and radiation treatment acted synergistically on fungal development resulting in 1.7% and 10.0% infection by B. cinerea and R. stolonifer, respectively, after 5 days at 23°C compared with 67% and 100% infection in the non-treated controls. Under natural infection conditions, hot water dip followed by irradiation at 0.5 KGy totally eliminated decay by Alternaria alternata during 8 days at 23°C. All treatments caused more rapid fruit softening, with 20% soft fruit in the combined treated fruit compared with zero soft fruit in the non-treated control.

Cultural conditions under which Penicillium digitatum and P. italicum develop were an important factor in determining the extent of their cellulolytic activity. At pH 5.5–7.5 of the culture medium, Cx-cellulase activity was correlated with mycelial dry weight. However, at pH 4.5 and more so at pH 3.5, activity was markedly reduced while fungal growth was not affected. Cx-cellulases of both species were not induced by the presence of carboxymethyl cellulose as a carbon source and were defined as constituent enzymes. Cellulase activity of the two Penicillia on different carbon sources was detected prior to the initiation of sporulation. A sporeless mutant of P. digitatum exhibited cellulolytic activity similar to that of the normal strain, suggesting no role for sporulation in the Cx-cellulase synthesis. Cx-cellulase activity in Valencia oranges started during the early stages of pathogenesis, before the appearance of disease symptoms. Correlation between the cellulase activity and the severity of the disease symptoms was apparent during the first three days after inoculation. At the end of the incubation period both fungi almost reached their maximum enzymatic activity, whereas the disease index continued to rise gradually until total fruit rot was achieved. A possible role of Cx-cellulases of the two Penicillia in the early stages of pathogenesis was suggested. Zusammenfassung Festgestellt werden konnte, das die Kulturbedingungen bei der Entwicklung von Penicillium digitatum und P. italicum einen wichtigen Faktor darstellten, die den Grad der zellulolytischen Aktivitat der Kulturen bestimmt. Die Cx-Cellulaseaktivitat war mit dem Mycekrockengewicht korreliert. Bei pH 4,5, und noch deutlicher ausgepragt bei pH 3,5, wurde die Enzymaktivitat stark reduziert, wahrend das Pilzwachstum nicht beeinflust wurde. Cx-Cellulasen von beiden Spezies wurden durch das Vorhandensein von Carboxymethylceilulose als C-Quelle nicht ausgelost und wurden als wesentliche Enzyme definiert. Eine Cellulaseaktivitat der beiden Penidllium-Spezies wurde bei verschiedenen C-Quellen vor Beginn der Sporenbildung festgestellt. Eine sporenlose Mutante von P. digitatum zeigte eine cellulolytische Aktivitat, die dem normalen Stamm sehr ahnlich war. Dies deutet darauf hin, das die Sporulation keine Bedeutung bei der Cx-Cellulasesynthese hat. Eine Cellulaseaktivitat konnte in Valencia-Orangen wahrend des sehr fruhen Stadiums der Pathogenese festgestellt werden, fruher als die ersten Befallssymptome sichtbar waren. Eine Korrelation zwischen der Cellulaseaktivitat und der Starke der Befallssymptome konnte wahrend der ersten drei Tage nach der Inokulation beobachtet werden. Zum Ende der Inkubationsperiode war die hochste Enzymaktivitat bei beiden Pilzspezies fast erreicht, die Befallsstarke jedoch entwickelte sich standig weiter, bis eine totale Fruchtfaule erzielt war. Eine mogliche RoUe der Cx-Cellulasen der zwei Penicillium-Spezies in den fruheren Stadien der Pathogenese wird erwogen.

Harvested ‘Galia’ melons (Cucumis melo L.) were dipped in hot water, wrapped in PVC stretch film and subjected to shelf-life trials. A dip time of 1–2 min in 55°C water was found to be the optimum anti-fungal treatment while a higher temperature or longer exposure time resulted in heat injury to the fruits. Wrapping dampened fruits before treatment, as a means of preventing reinfection of the fruit after heating, through exposure to the ambient air, resulted in heat injury due to the longer dip time required. Wrapping the fruits while still wet from the hot water treatment provided effective, antifungal protection for the melons for 9 days at 18°C without any retention of the excess water under the wrapping which would enhance decay development. This technique shortened the exposure time to possible reinfection to only a matter of seconds after heat treatment.

Publisher Summary Aflatoxins are found in fruits of tropical and subtropical regions, where typical environmental conditions support growth of aflatoxigenic aspergilli, and mycotoxin production. Aspergillus species are widespread in nature. They are regarded as soil fungi, frequently colonizing plant debris and decaying agricultural crops, and are among the commonest airborne fungi. They occur with high frequency as saprophytes on a wide range of substrates, including foods and feeds, and several species are among the typical pathogens of harvested fruits and vegetables. During their life cycle, several Aspergillus species are capable of producing a wide range of mycotoxins harmful to humans and animals that consume them. The major mycotoxins associated with Aspergillus species in fruits and vegetables are aflatoxins produced mainly by aflatoxigenic strains of A. flavus and A. parasiticus in figs and dates and ochratoxin A (OTA) produced by A. carbonarius and other ochratoxigenic aspergilli in grapes, dried vine fruits and wines. Some of the mycotoxins produced by Aspergillus species during their developmental stages in fruits and vegetables are among the most important carcinogenic mycotoxins; they include aflatoxins, ochratoxin A (OTA) and sterigmatocystin.

Publisher Summary This chapter provides an overview of Penicillium expansum, the cause of the destructive blue mold rot of pome and stone fruits. It is a major concern for human health, because of the production of patulin during pathogenesis. Human exposure is primarily via consumption of infected apple juices and other apple-based products. Patulin occurrence has been reported in juices of other fruits, such as pears, grapes, cherries, apricots and oranges. The factors affecting P. expansum growth and patulin formation include fungal strain, host fruit cultivar, and storage conditions, especially the storage atmosphere. The chapter discusses the worldwide occurrence of patulin in fruit products. It also explains patulin contamination in infant apple products, and comparisons between its levels in—organic fruits versus conventional ones, industrial versus hand-made products, and cloudy versus clear apple juices. Penicillium mycotoxins other than patulin, including ochratoxin A, citrinin, penicillic acid, cyclopiazonic acid, and penitrem, as well as the co-occurrence of different mycotoxins, are also discussed.

Isolates from a dark brown discoloration found in the embryonic tissue of popcorn seed lots showed that 81% of the seeds were invaded with moulds. Aspergillus chevalieri was by far the most common fungus inhabiting the embryonic tissue, followed by A. ochraceus, A. repens, Penicillium frequentans and A. melleus.

This chapter focuses on the biological control that refers to the use of naturally found microorganisms that antagonize the postharvest pathogens. Antagonism between microorganisms is a ubiquitous phenomenon involving fungi and bacteria, which naturally inhabit the soil and the surfaces of various plant organs. It is assumed that biocontrol of plant diseases occurs naturally on aerial plant surfaces, and may be one of the main reasons that crops are protected to some extent during their cultivation. One of the approaches to the isolation of antagonistic microorganisms for controlling postharvest diseases is through the promotion and management of natural epiphytic antagonists, which are already present on fruit and vegetable surfaces. Preharvest pesticide application and various postharvest treatments, such as fungicide and wax sprays, washes and dips, can greatly affect the resident microflora, both qualitatively and quantitatively.

Fruits become more susceptible to invasion by postharvest pathogens as they ripen. Treatments and conditions that lead to delayed ripening and senescence can, therefore, indirectly suppress postharvest disease development. These include low-temperature storage, low-O 2 and high-CO 2 atmospheres, ethylene removal from the atmosphere, growth regulators, calcium application; these, as well as other treatments or strategies, may contribute to maintaining the natural resistance typical of the young fruit or vegetable. Low temperatures that affect host and pathogen simultaneously prevent moisture loss from the host tissues and consequent shriveling; they retard metabolic activity and delay physiological changes that lead to ripening and senescence. Since fruits and vegetables become generally more susceptible to pathogens as they mature and approach senescence, the retardation in the physiological activity of the host is accompanied by a delay in decay development after harvest.

This chapter deals with the synthetic fungicides, which are the primary means used for controlling postharvest diseases. The resistance developed by postharvest pathogens to some fungicides, and the withdrawal of a number of key fungicides in response to health concerns over pesticide contamination, have stimulated the search for alternative technologies for postharvest disease control. Among the various possible alternative means of control, much attention has been drawn to the wide range of natural substances with antimicrobial activity. The chapter also examines inducible resistance in harvested tissues, which has recently joined the general concept that resistance in plants can be enhanced by modulating their natural defense mechanisms. Activation of defense responses in harvested crops has been demonstrated in various host–pathogen interactions via application of physical, chemical, or biological elicitors.

This chapter concentrates on the secretion of extracellular enzymes and toxins, which are the two major attack means with which the pathogen may be equipped, and the ability of the pathogen to detoxify host defense compounds. It also defines the cutinase enzyme, which hydrolyzes the primary alcohol ester linkages of the polymer. Cutin is found in many plant pathogenic fungi, including Botrytis cinerea . However, the importance of this enzyme for penetration of the cuticle seems to be a matter of debate. Many lines of evidence suggest that cuticular penetration of Colletotrichum gloeosporioides into the host is associated with the induction of extracellular cutinase production, and that insertion of the cutinase gene into this pathogen facilitates infection of an intact host. The chapter also explains the pectic substances, which constitute an important component of the primary cell wall of plants, and form the major component in the middle lamella, which are responsible for the tight link between the cells and the integrity of the plant tissue.

This chapter discusses the means for maintaining host resistance and other physical means: heating, ionizing radiation, and ultraviolet illumination. It defines the heat treatment that may be applied to the commodity by means of hot water dips and sprays, hot vapor or dry air, or infrared or microwave radiation. Practical systems have used mainly hot water or vapor. While hot water was originally used for fungal control and was extended to removal of insects from fresh commodities, vapor heating—developed for insect control—may also serve to reduce fungal decay. Thus, the vapor heat treatment used for disinfestation of Carabao mangoes in the Philippines also significantly reduced the incidence of anthracnose and stem-end rot in fruit, although the onset of decay was not delayed by the treatment.

This chapter discusses pathogens and their origin. During the prolonged storage of fruits and vegetables, a series of physiological processes occurs, which leads to the senescencing of the vegetal tissues and, in parallel, to their increased susceptibility to weak pathogens that attack senescencing vegetal tissues. Fungi and bacteria responsible for in-storage decay often originate in the field or the orchard. When penetration into the host takes place in the field, the pathogen, which is then in its early or quiescent stages of infection, will get to the storeroom within the host tissue without eliciting any symptoms of decay. The chapter also deals with spore germination, which is a preliminary stage to fungal penetration into the host. The right environmental temperature, available water or moisture and, sometimes, the presence of nutrients transferred from the host into the water, are the most important environmental factors that aid spore germination.

The postharvest infection of fruits and other plant organs may induce a number of alterations in their physiological and biochemical processes, or in the host tissue constituents, as a result of host–pathogen interactions. Process changes may include acceleration of ethylene evolution, stimulation of the respiratory enzymes, enhanced pectolytic activity, altered protein synthesis or polyamine-synthesis enzyme activity, and tissue changes may include increased cell-wall soluble pectin, and changed organic acid and sugar contents. The chapter also explains the ethylene synthesis, which is stimulated by mechanical wounding, which occurs while introducing the inoculum into the host. However, comparison between rates of ethylene production elicited by wounds of certain dimensions and those elicited by fungal lesions of similar size indicates that ethylene production in fungus-infected fruits is considerably greater than that in wounded ones.

Chemical substances intended for controlling postharvest diseases may be fungicides and bactericides, or fungistats and bacteristats. To serve its purpose, the chemical should come into contact with the pathogen; the minimal effective concentration is pathogen dependent. Chemical treatments can be applied under various strategies and with various timings: preharvest application to prevent infection in the field, sanitation procedure to reduce the level of inoculum in the environment to which injured fruits or vegetable are liable to be exposed, and postharvest application to prevent infection through wounds and to eradicate or attenuate established infections to prevent their development and spread during storage. In order to choose the appropriate strategy for decay control, one has to understand the mode of infection of the pathogen, its time of infection, and the environmental factors that may affect disease development.

This chapter highlights pathogen development within the host, which is correlated in many cases with the activity of cell wall-degrading enzymes. These enzymes are also responsible for cell death and the liberation of nutrients, which then become available to the pathogen. Liberation of nutrients results in a stimulation of pathogen growth and accelerated disease development. This may explain the great importance attributed to compounds that are capable of suppressing or preventing enzymatic activity. The chapter also defines the Polyphenols and tannins as inhibitors of polygalacturonase (PG) activity of Sclerotinia fructicola (Monilinia fructicola) in apples and other pathogen/host combinations, although they have no effect on the pathogen itself. Decay development in many fruits and vegetables may be the result of the delicate balance between active production of enzymes and their inhibition by polyphenols, mainly in their oxidized condition, as a result of polyphenol-oxidase activity.

This chapter discusses the characteristic pathogens of various fruits and vegetables. Each fruit and vegetable has its own group of characteristic pathogens to which it is susceptible, and for which it serves as a suitable host. Harvested fruits and vegetables are naturally attacked by a relatively small group of pathogens: approximately forty species. Moreover, each fruit or vegetable has its own typical pathogens out of this particular group. Fruits of tropical and subtropical origin, such as mango, papaya, avocado, or citrus fruits are typically attacked by the fungus, Colletotrichum gloeosporioides, which causes anthracnose. This pathogen penetrates into the fruit while still in the orchard, but the anthracnose symptoms in the rind break out only as the fruit ripens after harvest. In a similar manner, Gloeosporium musae attacks the unripe banana fruits in the orchard, to initiate a quiescent infection, which becomes active only during storage.

This chapter reviews preharvest factors that affect disease development, along with harvesting, and handling. The first preharvest factor which may affect postharvest quality is the cultivar, since different cultivars may vary greatly in their susceptibility to diseases. In fact, one of the aims of plant breeding and genetic engineering is to incorporate resistance genes in new varieties of crop plants. Differences in cultivar characteristics can markedly affect the keeping quality of the fresh produce. Another preharvest factor is the health of the planting material. Various pathogens may contaminate the planting material and cause disease in the field or in storage. Many pathogens persist in the soil or survive on plant debris in the field, from which winds and rain may be directly responsible for their dispersal to potential hosts. Other pathogens, such as Phytophthora spp., which infect potato tubers or citrus fruits, are actually dependent on rainwater for germination of their spores and initiation of infection.

‘Galia’ melons (Cucumis melo cv. Reticulatus) exported from Israel to Europe, are treated with 2000 ppm imazalil. The fungicide is incorporated in the wax used to coat the melon. This treatment protects the fruit against decay caused by Alternaria alternata and Fusarium spp., and leaves a residue of 4–5 ppm imazalil in the fruit. This amount exceeds the tolarance of some European countries who allow a residue below 0.5 ppm. To overcome this problem, other application methods were tested. Dipping or spraying the melons with 250 ppm imazalil in water followed by waxing, was as effective as the standard treatment while leaving a residue of 0.5 ppm. Testing other fungicides such as prochloraz and orthophenylphenol (OPP) confirmed that much smaller amounts are needed for decay control when applied in water.

Acetaldehyde (Aa) vapors inhibited development in vitro of the eight species of yeasts tested, fungicidal action being a function of concentration and length of exposure. The nonfermentative species Crytococcus difluens was the most sensitive species, 99% of its cell population being inactivated by exposure to 0.5% for 5 hr. Exposure to 0.5% for 10 hr was lethal to almost all species tested. A similar result was obtained by exposing the yeasts to a higher Aa concentration (3%) for a shorter period of time (3 hr). A concentration of 1% Aa, given for 1, 3 and 5 hr, was not lethal to the species tested but reduced the survival percentage of all yeast populations and usually caused a prolongation of the incubation period in culture. Colonization of Schizosaccharomyces pombe, the main factor responsible for the spoilage of natural concentrated citrus juices, was markedly inhibited by Aa vapors.

The production of zearalenone by an isolate of Fusarium equiseti was studied in chemically defined medium and in corn grains stored under modified atmospheres. An increase in the concentrations of sucrose or xylose in Czapek's medium resulted in increased toxin production, while no toxin was produced when lactose was present in the medium. Methionine (10−2 and 10−3 M) and cystine (10−3 M) added to Czapek's medium inhibited zearalenone production. When amino acids or nitrogen salts were added as the sole nitrogen source, only alanine, tryptophan and NH4Cl totally inhibited zearalenone production. Zearalenone production was inhibited almost completely in high-moisture corn grains (27%) kept under atmospheres enriched with high CO2 levels (60%, 40% or 20%) with either 20% or 5% O2. However, a lower amount of CO2 was needed to inhibit fungal development and toxin formation when a reduced O2 level was applied.

Five species ofAspergillus were isolated from post-harvest decays of pears, apples, peaches, grapes, strawberries, melons and tomatoes.A. niger was the most common species and was isolated from all types of fruits. Next in frequency wasA. flavus, which was infrequently isolated from stored grapes, tomatoes and peaches.A. wentii, A. ochraceus andA. tamarii were each cultured from only one type of stored fruit.

SUMMARY Fumigation with methyl bromide (MeBr) at a concentration of 120 mg/1 maintained for 4 h at 25°C caused 100% mortality of spores of Aspergillus ochraceus, A. flavus, Penicillium citrinum, P. chrysogenum and P. cyclopium. However, 40% of an A. niger spore population retained its viability after this treatment. Increasing the duration of fumigation to 24 h at a concentration of 40 mg/1 MeBr caused 100% spore mortality of all fungi tested. Total growth inhibition of 24 h-old mycelia was achieved with 40 mg/1 for 24 h or 120 mg/1 for 4 h. These concentrations for the same period of exposure were not inhibitory for 7-day-old mycelia of any of the fungi tested. In A. niger-inoculated wheat grains fumigated with 100 mg/1 MeBr for 24 h, 20% yielded fungal contaminants after 16 days of storage and 100% after 29 days. There was a marked drop in the percent germination of the grains after fumigation, whereas the free fatty acids level was higher than in unfumigated grain. The results of the in vivo study suggest that MeBr given at a commercial dosage for 24 h is not only ineffective in destroying the internal inocula of wheat grains but also enables their subsequent development by weakening the resistance of grains to fungal attack.

Shipments of corn imported to Israel from the U.S.A. during 1985 were sampled during unloading and examined for the presence of fungi and the trichothecene deoxynivalenol (DON). The most frequent species found on the corn wasAspergillus flavus followed byA. versicolor; three otherAspergilli — A. niger, A. ochraceus andA. fumigatus — were found at a much lower frequency. DON analysis was performed by electron capture detection gas chromatography after derivatization with heptafluorobutyryl imidazole. At fortification levels of 0.1, 1 and 2 μg/g, recoveries of 80—100% were obtained. Although DON was not detected in any of the samples analyzed, the observation (in the shipments) of fungi belonging to the generaFusarium andAspergillus suggests a potential danger of mycotoxin contamination. The relatively high moisture content of the samples increased the likelihood of such a hazard.