Colonization of barley grain by Penicillium verrucosum and ochratoxin A formation in the presence of competing fungi

Colonization of barley grain by Penicillium verrucosum and the formation of ochratoxin A were studied, both in pure culture and when paired with Aspergillus flavus, Fusarium sporotrichioides, and Hyphopichia burtonii, at 20 degrees and 30 degrees C and at 0.97, 0.95 and 0.90 a(w) over a 3-week period. Grain colonization was assessed on the basis of visible molding, seed infection, and numbers of CFU and by observing hyphal extension on the grain surface by scanning electron microscopy. Ochratoxin A concentrations were assayed by enzyme-linked immunosorbent assay using a monoclonal antibody. Germination of P. verrucosum spores was unaffected by the presence of other species. However, seed infection under most conditions was markedly decreased, relative to pure culture, by the presence of A. flavus and H. burtonii, but only slightly by F. sporotrichioides. The number of CFU of P. verrucosum was only slightly decreased in the presence of other species under most conditions. Generally, production of ochratoxin A by P. verrucosum was inhibited, sometimes significantly, in the presence of A. flavus and H. burtonii, but was changed only slightly by the presence of F. sporotrichioides. There was occasionally temporary enhancement in ochratoxin A production with all species during the 3-week incubation period.