Patulin risk associated with blue mould of pome fruit marketed in southern Italy

Blue mould is one of the most important postharvest diseases of pome fruit in all producing countries. It is mainly associated to Penicillium expansum that produces the mycotoxin patulin, although other species might be involved. The aim of the present study was to characterise Penicillium isolates associated with blue mould decay of pome fruit marketed in Apulia region (southern Italy), and verify their ability to produce patulin in vitro. Twenty-nine isolates of Penicillium spp. were recovered from pome fruit showing visible blue mould symptoms, and analysed for patulin production. After fungal isolation, the fruits were singularly analysed for patulin content. In general, the isolates proved to produce patulin and most of the pome fruit contained significant amounts of patulin, but there was no quantitative correspondence between in vitro and in vivo toxin accumulation. Isolate identification at species level was based on DNA analysis by P. expansum species-specific primers and sequencing of ß-tubulin gene. Furthermore, fungal isolates were tested for the occurrence of the patN gene coding the enzyme isoepoxydon dehydrogenase (IDH), involved in patulin metabolic pathway and considered a useful indicator of critical control points for patulin contamination. All 26 isolates identified as P. expansum were positive for patN and produced patulin. Moreover, three pear isolates belonging to other Penicillium species were found. They were positive for patN, but only two actually produced patulin. It can be concluded that toxigenic P. expansum isolates are associated with blue mould of pome fruit marketed in Apulia, thus a rapid detection is important to avoid patulin contamination beyond regulatory limits. Nevertheless, the presence of patN gene alone cannot be considered a predictive assay for patulin production. An evaluation of its expression level should be carried out.