Aspergillus section Nigri in soil and grapes at harvest time from different grape growing regions in Argentina. Viena, Austria.

CHIOTTA, M.L; BARBERIS M; GIAJ MERLERA G; REYNOSO M.M.; COMBINA M; TORRES A.M.; CHULZE , S.N

Tullm

Congreso; Conference International Society for Mycotoxicology (ISM) - 2009.; 2009

International Society for Mycotoxicology (ISM)

The main source of ochratoxin A (OTA) in the wine production chain is due to the infection of grapes by black Aspergilli  at pre-harvest stage. The main ochratoxigenic black Aspergillus species occurring on grapes are the biseriate Aspergillus niger aggregate and Aspergillus carbonarius. They are opportunistic fungi that may occur and form OTA on grapes from veraison to harvest. Understanding the ecology of the black Aspergilli can provide tools for OTA management at all stages of grape production and processing. In the vineyard, the main inoculum source of OTA-producer fungi is the soil. The goal of this work was to evaluate the distribution of black Aspergilli in soil and grapes at harvest time in vineyards from the main wine- producer regions in Argentina.  Soil and grapes samples were taken, during the 2007/08 harvest season, from 16 vineyards distributed in 7 agro-ecological regions (La Rioja, San Juan, Patagonia, and 4 areas from Mendoza). The black Aspergillus species were isolated and identified by morphology, and by PCR using species specific primers based on partial calmodulin gene. In grape samples, the infection levels with black Aspergillus were dependent on the agro-ecological region evaluated, the highest levels were observed in Mendoza (North region), La Rioja and San Juan (53%, 47.5% y 46% respectively). Species belonging to Aspergillus niger aggregate were isolated in 86.6 % of the samples, followed by A. carbonarius (7.8%) and Aspergillus uniseriate (5.6%). A. carbonarius was isolated from 3 out of 7 regions evaluated, and the higher levels of infection were observed in samples obtained from San Juan and La Rioja. These later agro-ecological regions had semiarid climate, with low annual rainfall and strong solar radiation, with summer temperatures that  could raise up to 40ºC. In soil samples the UFC g-1 of black Aspergillus were significantly different among the regions evaluated, the highest count was observed in the Patagonia vineyards (18,500 UFC g-1), and the low count was observed in Mendoza (Valle de Uco region). There was not found correlation between the amount of soil inoculum and  the percentage of grape infection with black aspergilli,  only was observed   correlation between the presence of  A. carbonarius  in the  soil samples and  the grape samples  from the same vineyard.  All the A. carbonarius strains isolated were OTA producers, with a mean value of 16 ug g-1; while 9.8% of the strains belonging to A. niger aggregate were positive for OTA production, with a mean value of 0.98 ng g-1. Based on the results, the incidence of black aspergilli in grapes at harvest is not significantly correlated with the presence of these fungi in the soil. The incidence of   A. carbonarius in soil and grape samples  in Argentina is low, and it could be relevant only in some  agro-ecological regions from  the North of the country.