Aflatoxin and sterigmatocystin contamination of pistachio nuts in orchards.

Aspergillus flavus and A. versicolor were both shown to be weak pathogens of developing pistachio fruits, producing aflatoxin and sterigmatocystin, respectively. Aflatoxin concentrations approached those reported in cereal and legume seeds. Fungus lesions on the first hulls were followed by invasion of seeds despite the sclerified shell. Infections and mycotoxins present before harvest would presumably lead to further build-up after harvest if drying was slow or storage was under high humidity.

Aspergillus flavus infection and aflatoxin production in fig fruits.

Immature fig fruits did not support colonization and aflatoxin production by Aspergillus flavus Lk. but became susceptible when ripe. While sun-drying on the tree, fruits were particularly vulnerable to fungal infection and colonization. Aflatoxin accumulation equaled levels frequently reported for such seeds as peanuts and cereal grains.

Production of patulin by Penicillium expansum.

Twenty-seven isolates of Penicillium expansum Lk. ex Thom obtained from Europe, Australia, and North America from seven different fruit hosts all produced patulin in culture. Six isolates were essentially nonpathogenic in apple fruits. In culture, patulin generally accumulated to much higher levels than in apple fruits. At all temperatures permitting fungus growth, patulin was produced. However, only small amounts were observed near the maximal temperature for growth (30 C). At 0 C, patulin accumulated but slowly in culture. Modified atmospheres suppressed both fungus growth and patulin accumulation in apples. After varying incubation periods to obtain similar total growth, the patulin concentration was low in modified atmospheres and high in air.

Recovery of viability and radiation resistance by heat-injured conidia of Penicillium expansum Lk. ex Thom.

Spores heated in water at 54 C for up to 1 hr were plated on nutrient agar immediately or held for 3 days in aerated water at 23 C and then plated. Under these conditions, holding was optimal for recovery, increasing survival percentage up to 20-fold over values for immediate plating. Recovery was prevented partially or completely, however, when spores were held in any of the following solutions: glucose, potassium phosphate, ammonium or sodium acetate, sodium azide, or 2,4-dinitrophenol, or in the sodium or potassium salts of pyruvate, and tricarboxylic acid cycle acids. Both anaerobiosis and incubation at 0 C prevented recovery. Survivors of a heat treatment were more sensitive to gamma radiation than were unheated spores. Conditions which affected the recovery of viability had the same effect on restoration of radiation resistance. Thus, many of the processes for restoration of radiation resistance seem involved also in recovery of viability after heating. After a 99% inactivating treatment (about 30 min at 54 C), heated spores respired as fast as unheated spores, or faster. Malate, citrate, succinate, and acetate stimulated respiration in unheated spores and inhibited it in heated spores.

Ultrastructural changes in Rhizopus stolonifer sporangiospores in response to anaerobiosis.

Rhizopus stolonifer sporangiospores developed prominent ultrastructural changes under anoxia. Mitochondria were scattered randomly throughout the cytoplasm in spores incubated aerobically for 3 hr, but moved to the periphery of the cytoplasm when the spores were exposed to anoxia. Endoplasmic reticulum, inconspicuous in control spores, appeared near the plasmalemma and was frequently found connected to a nuclear membrane. The cytoplasm, otherwise usually uniformly dense and containing abundant ribosomes, appeared mottled under anoxia. The absence of ribosomes could account for the mottled appearance. Lipid inclusions were distinctively separated from the electron-transparent areas of the mottled cytoplasm. The increasing thickness of the inner wall indicated that the metabolic activity of spores continued under anoxia. When aerobic conditions succeeded anoxia, germ-tube protrusion occurred.

Ultrastructural details in germinating sporangiospores of Rhizopus stolonifer and Rhizopus arrhizus.

Electron microscope examination of sporangiospore sections from Rhizopus stolonifer (Ehrenb. ex Fr.) Lind. and R. arrhizus Fischer revealed details on intracellular organization not previously reported. Aldehyde fixation followed by chromeosmium postfixation permitted clear depiction of ribosomes hitherto unrevealed in these cells. Mitochondria were diversiform. Spore wall structures in the two species were generally similar, but outer contours differed sufficiently to permit easy species identification in examination of sections. The spores of both species abounded in cytosomes, corresponding in size, shape, and heavy-metal "stain" affinities to spherosomes in cells of higher plants. The osmiophilic response of these spherosome-like inclusions was intensified by treatment of sections with thiocarbohydrazide solution and subsequent application of aqueous osmium tetroxide, which strengthens an assumption that they are lipid-rich. The margins of the spherosome-like inclusions in lead citrate-stained sections included dense particles, about 60 A across, whose crystalline-like arrangements suggested that protein as well as lipid was present. Frequent and close associations between the spherosome-like inclusions and various cell membranes suggested that such bodies participate in membrane elaboration during germination.

Electron microscopy of Botrytis cinerea conidia.

Buckley, Patricia M. (University of California, Davis), Virginia E. Sjaholm, and N. F. Sommer. Electron microscopy of Botrytis cinerea conidia. J. Bacteriol. 91:2037-2044. 1966.-Sections of germinating and nongerminating Botrytis cinerea conidia were examined with an electron microscope. Uranyl acetate or lead citrate provided contrast between membranes and cytoplasm. Membrane-bounded, dense inclusions previously unreported in dormant spores were termed "storage bodies." Whorled structures, spherules, granules, and membrane loops were seen within these inclusions. The various forms assumed by the enclosed materials closely resemble phospholipid inclusions described for other cells. It is suggested that the inclusions provide material for the assembly of membranous organelles during germination. Utilization of the stored material apparently results in extensive vacuolization in advanced germinants.

Effect of gamma radiation on the ripening of bartlett pears.

Gamma radiation at doses of 300 Krad or more inhibits the ripening of Bartlett pears (Pyrus communis L.). Immediately after irradiation there is a transitory burst of C(2)H(4), which subsequently declines in fruits subjected to inhibitory doses. Ethylene production associated with ripening begins at the same time in unirradiated fruits and those subjected to noninhibitory doses, but the latter produces much more C(2)H(4) at the climacteric peak. Fruits subjected to inhibitory doses produce low levels of C(2)H(4) unless subjected to exogenously applied C(2)H(4), whereupon they produce enough of the gas to induce ripening in unirradiated fruits.Pears subjected to 300 and 400 Krad of gamma rays did not ripen even when held in a flowing atmosphere containing 1000 ppm of C(2)H(4) for 8 days at 20 degrees . It is concluded that the action of gamma rays on Bartlett pears involves both an inhibition of C(2)H(4) production and a decreased sensitivity of the fruit to the ripening action of the gas. Ripening of Bartlett pears is inhibited by gamma radiation only when applied to preclimacteric fruit.