Biocontrol activities of yeasts or lactic acid bacteria isolated from Robusta coffee against Aspergillus carbonarius growth and ochratoxin A production in vitro.

Biocontrol Agents (BCAs) can be an eco-friendly alternative to fungicides to reduce the contamination with mycotoxigenic fungi on coffee. In the present study, different strains of bacteria and yeasts were isolated from Ivorian Robusta coffee. Their ability to reduce fungal growth and Ochratoxin A (OTA) production during their confrontation against Aspergillus carbonarius was screened on solid media. Some strains were able to reduce growth and OTA production by 85 % and 90 % and were molecularly identified as two yeasts, Rhodosporidiobolus ruineniae and Meyerozyma caribbica. Subsequent tests on liquid media with A. carbonarius or solely with OTA revealed adhesion of R. ruineniae to the mycelium of A. carbonarius through Scanning Electron Microscopy, and an OTA adsorption efficiency of 50 %. For M. caribbica potential degradation of OTA after 24 h incubation was observed. Both yeasts could be potential BCAs good candidates for Ivorian Robusta coffee protection against A. carbonarius and OTA contamination.

The Influence of Long-Term Storage on the Epiphytic Microbiome of Postharvest Apples and on Penicillium expansum Occurrence and Patulin Accumulation.

Patulin is a secondary metabolite primarily synthesized by the fungus Penicillium expansum, which is responsible for blue mold disease on apples. The latter are highly susceptible to fungal infection in the postharvest stages. Apples destined to produce compotes are processed throughout the year, which implies that long periods of storage are required under controlled atmospheres. P. expansum is capable of infecting apples throughout the whole process, and patulin can be detected in the end-product. In the present study, 455 apples (organically and conventionally grown), destined to produce compotes, of the variety "Golden Delicious" were sampled at multiple postharvest steps. The apple samples were analyzed for their patulin content and P. expansum was quantified using real-time PCR. The patulin results showed no significant differences between the two cultivation techniques; however, two critical control points were identified: the long-term storage and the deck storage of apples at ambient temperature before transport. Additionally, alterations in the epiphytic microbiota of both fungi and bacteria throughout various steps were investigated through the application of a metabarcoding approach. The alpha and beta diversity analysis highlighted the effect of long-term storage, causing an increase in the bacterial and fungal diversity on apples, and showed significant differences in the microbial communities during the different postharvest steps. The different network analyses demonstrated intra-species relationships. Multiple pairs of fungal and bacterial competitive relationships were observed. Positive interactions were also observed between P. expansum and multiple fungal and bacterial species. These network analyses provide a basis for further fungal and bacterial interaction analyses for fruit disease biocontrol.

Impacts of abiotic factors on the growth of three commercial biological control agents, on the growth and mycotoxinogenesis of Fusarium graminearum and on their interaction.

BACKGROUND: Evolving climatic conditions impact the behavior of microorganisms. The lack of efficiency of beneficial microorganisms against pathogens can be due to these evolving abiotic factors more favorable to the development and adaptation of pathogens. It is therefore of great interest to understand their impact (especially temperature increase and relative humidity (RH) variation) on pathogenic and non-pathogenic microorganisms. This work aimed to examine the possible effects of increasing temperature (20, 25, 30 and 33 °C) and RH (40%, 50%, 60% and 80%) on the growth and mycotoxin production (deoxynivalenol (DON) and zearalenone (ZEN)) of Fusarium graminearum, on the growth of three commercial biocontrol agents (BCAs; Mycostop®, Xedavir® and Polyversum®) and on the pathogen-BCA interaction. RESULTS: Results demonstrated that BCAs have contrasting impacts on the growth and mycotoxinogenesis of F. graminearum depending on abiotic factors. At 25 °C and regardless of RH, commercial BCAs limit DON production by F. graminearum, but at 30 °C and intermediate RH, Xedavir® is no longer effective. The ability of Xedavir® to control the production of ZEN production by F. graminearum is also affected by abiotic factors. However, increasing temperature has an opposite effect on its ability to control the accumulation of ZEN. Polyversum® oomycete is the BCA with the most resilient efficacy against F. graminearum toxinogenesis under the different abiotic factors. CONCLUSION: This work provides new knowledge of the effect of these abiotic parameters on the interaction between BCA and F. graminearum, especially on the production of mycotoxins. It paves the way for the development of efficient and resilient mycotoxin biocontrol strategies using beneficial microorganisms against F. graminearum, thus contributing to global food security. © 2023 Society of Chemical Industry.