Mycobiota and toxicogenic Alternaria spp. strains in Malbec wine grapes from DOC San Rafael, Mendoza, Argentina

Alternaria, one of the most mycotoxigenic genus commonly found in wine grapes, could represent a high risk for wine consumer's health. The aims of this work were to identify the mycobiota of Malbec wine grapes under the influence of routine control viticulture practices, to identify Alternaria spp. strains by morphological and molecular methods and characterize their toxicogenic ability and pathogenicity. Alternaria was the main component of the wine grape mycobiota of the DOC San Rafael at harvest time (81%) followed by Cladosporium (7%) and only in minor percentage by Penicillium (4%) and Aspergillus (3%) among others. The application of an organic or non-organic treatment in the vineyard did not affect significantly the incidence of the present genera. According to morphological and molecular identification based on the genetic marker Alt a 1, all Alternaria isolates were included into Alternaria alternata species. Of 34 analyzed Alternaria strains, 97% were able to produce at least one of the three mycotoxins analyzed: alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TA) and 53% co-produced the three mycotoxins. TA was the toxin produced at highest frequency (97%) and at highest levels in a range from 11.2 to 1941.0 ppm. It was followed by AOH produced by 71% of the strains, in a range from 1.8 to 437.0 ppm and AME produced by 59% of the strains, in a range from 0.6 ppm to 663.4 ppm. The 55% of the Alternaria strains were very pathogenic, 31% moderately pathogenic and only 14% were slightly pathogenic. In the present work, a high incidence and prevalence of Alternaria genus was reported despite the use of routine control viticulture practices, as well as a high percentage of toxicogenic and pathogenic Alternaria strains.