V. De Cicco

Aureobasidium pullulans (LS-30) an antagonist of postharvest pathogens of fruits: study on its modes of action

In small-scale experiments Aureobasidium pullulans (isolate LS-30) displayed significant antagonistic activity against Botrytis cinerea, Penicillium expansum, Rhizopus stolonifer and Aspergillus niger on table grapes, and B. cinerea and P. expansum on apple fruit. To improve the performance of this yeast-like fungus, possible modes of action were investigated. Competition for nutrients appeared to play a role in the activity of this antagonist. Extracellular exochitinase [N-acetyl-b-D-glucosaminidase (Nagase)] and b-1-3-glucanase activities were also detected both in vitro and in apple wounds, which are the main sites of penetration of postharvest fungal pathogens, suggesting that these enzymes may actually be involved in the antagonistic activity of this microorganism. Neither antibiosis nor direct physical interaction of LS-30 cells with the hyphae of B. cinerea appeared to be involved in the activity of this antagonist.

beta-1,3-glucanase activity of two saprophytic yeasts and possible mode of action as biocontrol agents against postharvest diseases

Abstract The yeasts Rhodotorula glutinis (isolate LS-11) and Cryptococcus laurentii (isolate LS-28), showing different levels of antagonistic activity against a range of postharvest pathogens, were examined for their possible mode(s) of action, in order to highlight the reasons for the higher activity of isolate LS-28. Competition for nutrients appeared to play a role in the activity of both yeasts, especially in the case of isolate LS-11. Direct interaction with pathogen hyphae was shown only by cells of this same isolate, whereas no interaction with fungal hyphae was observed for the more active antagonist LS-28. The latter isolate was able to produce in vitro significantly higher levels of extracellular β -1,3-glucanase activity than LS-11 when grown in the presence of hyphal cell walls of the pathogens Penicillium expansum and Botrytis cinerea as sole carbon sources. In our experimental conditions, antibiosis did not appear to be involved in the activity of either antagonists.

Biocontrol by yeasts of blue mould of citrus fruits and the mode of action of an isolate of Pichia guilliermondii

SummaryNineteen yeast isolates, from different fruits, were tested for antagonistic activity against blue mould (Penicillium italicum) on artificially wounded citrus fruits. Strains 1 A, 5A, and 29A of Pichia guilliermondii, strains 21D, 22D and 30F of Candida famata and strain 13 L of C. sake reduced infection from 86 to 98% compared with the control. Isolate 5 A of P. guilliermondii was the most effective antagonist and its mode of action was investigated further. Its activity against the pathogen declined when the number of yeast cells inoculated in the wound was reduced although it showed good ability to colonize the wound site and grow rapidly, cell numbers increasing by up to 60-fold within 24 h. Scanning electron microscopy of the wound also showed attachment of the yeast cells to the pathogen hyphae. The high antagonistic activity of isolate 5A appeared to be related to its capability to occupy space and use nutrients available in the wound, thus depriving the pathogen of them. It also induced in ...

Integration of Biocontrol agents and food-grade additives for enhancing protection of stored apples from Penicillium expansum

Forty-nine compounds currently used as additives in foods were tested in combination with three biocontrol agents, the yeasts Rhodotorula glutinis, Cryptococcus laurentii, and the yeastlike fungus Aureobasidium pullulans, to increase their antagonistic activity against Penicillium expansum, the causal agent of blue mold on apples. Twelve additives dramatically improved the antagonistic activity of one or more of the tested biocontrol agents. In a two-way factorial experiment with these selected additives the percentage of P. expansum rots on apples was significantly influenced by the antagonist and the additive as well as by their interaction. The combination of the biocontrol agents and some additives resulted in a significantly higher activity with respect to the single treatments applied separately, producing additive or synergistic effects. Some of the selected additives combined with a low yeast concentration (106 cells per ml) had comparable or higher efficacy than the biocontrol agents applied alone at a 100-fold higher concentration (10(8) cells per ml). Some organic and inorganic calcium salts, natural gums, and some antioxidants displayed the best results. In general, the effect of each additive was specific to the biocontrol isolate used in the experiments. Possible mechanisms involved in the activity of these beneficial additives and their potential application in effective formulations of postharvest biofungicides are discussed.

Environmental factors affect the activity of biocontrol agents against ochratoxigenic Aspergillus carbonarius on wine grape.

The influence of temperature and relative humidity (RH) on the activity of three biocontrol agents-the yeast Metschnikowia pulcherrima LS16 and two strains of the yeast-like fungus Aureobasidium pullulans LS30 and AU34-2-against infection by A. carbonarius and ochratoxin A (OTA) accumulation in wine grape berries was investigated in lab-scale experiments. The presence of wounds on grape skin dramatically favored infection of berries by A. carbonarius strain A1102, since unwounded berries showed very low levels of infection at all conditions of RH and temperature tested. Artificially wounded berries pre-treated with the biocontrol agents were inoculated with the ochratoxigenic A. carbonarius strain A1102 and were incubated for 5 days at two levels of RH (60% and 100%) and three different temperatures (20, 25 and 30 °C). The three biocontrol agents were able to prevent infections at 60% RH and 20 °C. At 60% RH and 25 °C only strain AU34-2 achieved some protection on day 5, whereas at 30 °C a limited biocontrol efficacy was evident only up to day 2. At 100% RH, LS16, LS30 and AU34-2 showed effective protection of grape berries at 20 °C until the 5th day of incubation. The three biocontrol agents achieved significant protection at higher temperatures only until the 2nd day after the beginning of the experiment: all three strains at 25 °C, and only strain LS16 at 30 °C. After 5 days, the three biocontrol agents were able to significantly reduce the level of OTA in berries at all the conditions tested. This occurred even when protection from infection was not significant, except at 30 °C and 100% of RH for all the three strains, and at 25 °C and 100% of RH for strain LS16. The biocontrol agents displayed a higher rate of colonization on grape berries at 20 and 25 °C than at 30 °C. The higher value of RH (100%) appeared to increase the rate of colonization, in particular at 20 and 25 °C. Taken together, our results emphasize the significant influence of environmental factors on the effectiveness of biocontrol against A. carbonarius as well as on OTA contamination in wine grape berries, and the need for biocontrol agents that can cope with the environmental conditions that are conducive to attack by A. carbonarius.