Detection and toxigenic evaluation of endophytic strains of Aspergillus flavus from Italian rice seeds

Ten strains of A. flavus, all characterized by a very slow rate of hyphal production from the plated seeds (from two to four weeks of incubation), were respectively isolated from ten cultivars. In particular, seven strains were detected from shattered seeds (belonging to cvs. Ares, Belgioioso, Delfino, Elvo, Idra, Maratelli, Venere) and three strains from sterilized but not broken seeds (cvs. Dedalo, Gemini, Perseo). As different seeds of the same cultivar were always endophytically colonized by the species, results were expressed as per cent number of colonized seeds. The highest percentages of A. flavus were detected in seeds of cvs. Belgioioso (50%), Delfino (39%), Maratelli (30%) and Idra (21%); the lowest in seeds of cvs. Perseo (8%), Dedalo (6%), Ares (6%), Gemini (4%), Venere (3%), Elvo (2%). When transferred onto PDA medium, all the strains started to produce a large quantity of brown to black, globose to subglobose, about 500 µm in diameter sclerotia. Supported by an extremely positive correlation between the production of both sclerotia and mycotoxins, individuated in some atypical A. flavus studied by Saito et al. (1986), the toxigenic activity of all rice strains was analyzed.