First report: Penicillium adametzioides, a potential biocontrol agent for ochratoxin-producing fungus in grapes, resulting from natural product pre-harvest treatment

Abstract

Ochratoxin A (OTA) is a secondary metabolite produced mainly by Aspergillus section Nigri (Aspergillus carbonarius is the most relevant strain in the Mediterranean region with a group 2B carcinogenic effect in humans. In vivo experiments were conducted in southern France involving applying pre-harvest Stifénia® (elicitor), Scala® (chemical fungicide) and two other control treatments [not contaminated by A. carbonarius (OTA-PF) and not treated and artificially contaminated by OTA-PF but not treated]. The Stifénia® and Scala® treatments significantly reduced the OTA juice contamination so that it was under the authorised uptake OTA limit. Stifénia® highly affected the grape fungal ecosystem with new non-Aspergillus strains isolated from grape stems and juices. In vitro antagonistic tests were performed with Stifénia® non-Aspergillus isolates (n = 10). Three antagonistic tests were applied using different distances (3 and 5 cm in between the two microorganisms) with two different inoculation times (at the same time and with three day intervals in between). Certain strains had a positive mycelial growth effect on A. carbonarius colonies, such as Penicillium spp. and Fusarium sp. Other strains displayed a reduction effect on OTA production of OTA-PF, such as Penicillium spp. (J2, J3). Penicillium adametzioides (S3) and Penicillium expansum (J1) (at certain stages) reduced the OTA production and mycelial growth. P. expansum was excluded as a bio-control agent because of its mycotoxin production ability. The higher challenge distance between certain strains of P. adametzioides (S3) and other Penicillium strains (as J1, J2, J3 and J4; at three and seven days) reduced the secretion of OTA by OTA-PF. This OTA production reduction could possibly prevent OTA contamination prevention in the case of epidemic favourable conditions by reducing the OTA produced in grape post-harvest products (i.e., juice). This could be accomplished by applying as the elicitor one of the tested fungi with an antagonistic effect on OTA production, such as P. adametzioides (at 10 days). Certain strains, such as P. adametzioides (S3) and J2 (P. spp.) should be further investigated to determine the details of the underlying mechanism of their OTA reduction and their ecosystem effects in cases of in vivo application.