Mode of action of potential biocontrol agents against Fusarium species and Cochliobolus sativus

ABSTRACT

The antagonistic activities of three potential biocontrol agents (BCAs), Clonostachys miodochialis, C. rosea, and Minimedusa polyspora, were tested in vitro against the target fungi Fusarium acuminatum, F. avenaceum, F. equiseti, F. graminearum, and Cochliobolus sativus. In vitro dual-culture assay revealed that the BCAs were able to inhibit the mycelial growth of most of the target fungi, with the most common mode of action being mycoparasitism. After 5 d of incubation, depending on the host-parasite interface, biotrophic mycoparasitism was observed via attachment structures on F. avenaceum, F. equiseti, and C. sativus. Haustoria and appressoria were formed by C. miodochialis and M. polyspora on F. avenaceum and C. sativus, respectively. Clamp-like structures were also produced by both BCAs, depending on the host fungus. Clonostachys rosea formed only contact points on its hosts. Coiling structure was observed with C. rosea and M. polyspora occasionally in pure culture but more abundantly in the dual-culture assay. After an additional 3 to 5 d of incubation, the BCAs started damaging their host cells. Asexual fruiting bodies of the BCAs spread necrotrophically on F. acuminatum and F. graminearum and began destroying their mycelia after the initial 5 d of incubation. Furthermore, mycelial dissolution of F. acuminatum by an excreted substance was observed at a distance before direct contact with C. miodochialis. The diffuse metabolite assay revealed that the highest inhibition of the three BCAs was on C. sativus and their least effectiveness was observed on F. graminearum. Overall, these results provide evidence that C. miodochialis, C. rosea, and M. polyspora are potential candidates for biological control of the tested target fungi. This constitutes the first report that these three BCAs are able to establish an initial biotrophic relationship followed by a necrotrophic lifestyle. In addition, C. miodochialis has not previously been reported as a BCA.

KEYWORDS:

• BCAs
• biotrophic
• host
• mycoparasitism
• necrotrophic
• pathogens

ACKNOWLEDGMENTS

We thank Shania Rados for technical assistance.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We gratefully acknowledge funding by Prairie Heritage Seeds Organics Inc., Saskatchewan Wheat Commission, Alberta Wheat Commission, and the Agri Science Program under Agriculture and Agri-Food Canada’s Canadian Agricultural Partnership, through the Organic Science Cluster 3, led by the Organic Federation of Canada in collaboration with the Organic Agriculture Centre of Canada at Dalhousie University. We are also grateful for the in-kind contributions from the Advisory Committee on Organic Research for the Swift Current Research and Development Centre.