Ecology of the ochratoxin A producing Penicillium verrucosum:: Occurrence in field soil and grain with special attention to farming system and on-farm drying practices

Mycotoxin contamination of organically grown cereals has been a growing concern during recent years, one of the most important being ochratoxin A (OTA). In countries with a temperate, humid climate, OTA is produced by Penicillium verrucosum and it is crucial to focus on the fungus to obviate problems. This paper presents results to elucidate different aspects of the ecology of P. verrucosum. In a survey of differently farmed soils, P. verrucosum was found in 11 out of 65 soils, 35% of the organically and 7% of the conventionally cultivated, these being the first reports of its natural occurrence in soil. Except for two soils, it was found with low frequencies (100-300 cfu g dry soil(-1)), and the results point to home grown seed as a potential risk of soil contamination. In a survey of organically grown grain, P. verrucosum was found in 51% of the recently combined and not yet dried grain samples; 60% of the rye and 53% of the wheat samples. This confirms that early contamination does take place and increases the demand for proper grain handling during drying and storage. Three case studies were performed at organic farms with different storage facilities. The results showed very clearly that there is no general risk of OTA contamination in organically cultivated grain. Within the same year, major differences between the farms were found and these differences were reproduced during three growing seasons. It therefore seems likely that an organic farming system, as such, does not present problems in relation to OTA contamination. It is, rather, certain management practices that are inappropriate and these management practices may be more prevalent in organic farming. This assumption is discussed in relation to home grown seed, crop rotation, organic fertilizers, exclusion of pesticides, and drying and storage facilities.