Surveillance of ochratoxigenic fungi in different inoculum sources from Argentinean vineyards

PONSONE, L; COMBINA, M; DALCERO, A; CHULZE, S.N

Florianopolis, Brasil

Congreso; Congreso Latinoamericano de Micotoxilogia; 2006

Sociedad Latinoamericana de Micologia (SLAM)

Ochratoxin A (OTA) is a nephrotoxic mycotoxin naturally found in a wide range of food commodities throughout the world. The IARC has classified OTA as ?possibly human carcinogen?. Since the first description of OTA production by species belonging to Aspergillus section Nigri, the significance of black aspergilli as toxin producing fungi was changed through the years. It is now considered that in substrates such as grapes, raisins and wine  the main source of OTA contamination detected is due mainly to A carbonarius and the species included in the A niger aggregate. The objectives in the present study were to isolate and identify the Aspergillus populations associated with grapes, weeds, soil and pods debris; to evaluate the toxigenic potential of the identified isolates with regard to ochratoxin production. Fifty samples of each substrate were collected from four vineyards located at 85 Km Eastern of Mendoza city 33º 16? South Latitude 68º 09? West Longitude. The samples were taken during different phases of grape development: setting, one month after setting, early veraison and at harvest. The vineyards chosen were representative of the grape growing area as regards grape variety and farming methods. Isolation and quantitative enumeration of fungal propagules were done on Dichloran 18% Glycerol Agar (DG18) and Dichloran Rose Bengal Chloramfenicol Agar (DRBC). Identification of the Aspergillus species was done according to Pitt and Hocking (1997). The ability of produce OTA by the potential ochratoxigenic species was evaluated on YES (2% yeast extract, 15% sucrose) medium. The cultures were incubated at 30 ºC ± 1 ºC for 10 days in darkness. Most samples were colonized by A niger aggregate in all growth stages. A carbonarius specie were also present, although their frequency of isolation was low. A. japonicus, A. aculeatus, and A. foetidus were also isolated, but the distribution varied according to the growth stage, the grape variety and the cropping system. From 246 black Aspergillus strains isolated from grapes, 26.4 % were OTA producers in levels ranging from 1.3 to 50.61 ng/mL. While from 110 black Aspergillus strains isolated from pod debris, 34,8 % were OTA producers in levels ranging from 1.1 to 22.6 ng/mL. Among the strains isolated from weeds 15.5 % were OTA producers with levels ranging from 1.2 to 45.9 ng/mL. From the strains isolated from soil, 34 % were OTA producers with levels ranging from 1.7 to 42.3 ng/mL. Although the toxigenic potential is low, the incidence of toxigenic species of Aspergillus section Nigri in Argentinean vineyards requires the implementation of continuing monitoring for OTA contamination of grapes entering to food chain.