Alternaria SPP. in food commodities of Slovak origin: occurrence and mycotoxin production abilities

Various food commodities of Slovak origin were analysed for the occurrence of Alternaria species-groups. Totally we analysed 14 samples of grapes, 3 samples of barley, 2 samples of wheat, 17 samples of fruit, vegetable and fruit-vegetable juices, 6 samples of red kuri squash with macroscopically visible infection. Mycological analyses were performed by using plate dilution method, method of direct placing of berries or grains on the plates with dichloran, rose bengal and chloramphenicol agar or by direct inoculation by mycological needle to the identification medium (potato-carrot agar). In all grape, barley, wheat and squash samples the presence of representatives of this genus was detected (100% isolation frequency). In juices, 41% of the samples were positive for their occurrence. The highest relative density of Alternaria isolates was found in grape samples (87%). All detected strains were segregated into four morphological species-groups: A. alternata, A. arborescens, A. infectoria and A. tenuissima. The most dominant species-group in grapes was A. arborescens, in barley and wheat A. tenuissima, followed by A. alternata, in juices only A. alternata and A. arborescens species-groups were detected and isolates of squashes were not classified to the species-groups. Randomly selected 67 isolates were analysed for the ability to produce mycotoxins alternariol (AOH), alternariol monomethylether (AME) and altenuene (ALT) by means of thin-layer chromatography. Of all tested isolates, AOH production was most frequently reported (70% of tested isolates). AME was produced by 60% and ALT by 49% of tested isolates. The largest share of the productive strains originated from the squashes, where all tested isolates produced ALT and AOH, followed by isolates of juices. From the viewpoint of individual species-groups, A. arborescens isolates and Alternaria spp. appeared to be the most productive in all mycotoxins tested.