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ABSTRACTThe 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. miodochialisand M. polysporaon F. avenaceumand C. sativus, respectively. Clamp-like structures were also produced by both BCAs, depending on the host fungus. Clonostachys roseaformed only contact points on its hosts. Coiling structure was observed with C. roseaand M. polysporaoccasionally 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. acuminatumand F. graminearumand began destroying their mycelia after the initial 5 d of incubation. Furthermore, mycelial dissolution of F. acuminatumby 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. sativusand their least effectiveness was observed on F. graminearum. Overall, these results provide evidence that C. miodochialis, C. rosea, and M. polysporaare 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. miodochialishas not previously been reported as a BCA.

There has been a steady expansion in organic production in the Canadian Prairies because of higher consumer demand. Thus, increasing the sustainability of organic systems would be important. An organic trial was conducted in the semi‐arid Prairies (2010–2015) with two tillage intensities (low vs. high) in a simplified [spring wheat (Triticum aestivumL.)–forage pea (Pisum sativumL.) green manure (GM)] and a diversified (spring wheat–oilseed–pulse–GM) rotation. In 2013–2015, the impact of these systems on root rot was examined on spring wheat, pulses, and GM crops. Several Fusariumspp. were more abundant in GM and pulses than spring wheat, suggesting that they could be a source of inoculum, especially of F. avenaceum(Fr.:Fr.) Sacc. (teleomorph Gibberella avenaceaCook), for Fusariumdiseases in cereals including Fusarium head blight. Under different environments, tillage–rotation systems had an impact on root disease and fungal populations, some of which have biocontrol capabilities. There was no difference among systems for root rot in forage pea, while the low tillage‐diversified rotation had the lowest root rot in spring wheat but was associated with more Fusariumspp. For all crops, most Fusariawere not associated with root rot severity. Cochliobolus sativus(Ito & Kurib.) Drechs. ex Dast. [anamorph Bipolaris sorokiniana(Sacc.) Shoemaker] accounted the most for root rot in spring wheat and was favored by intensive tillage and simplified rotations. The Shannon diversity index (H') of fungal species in spring wheat was higher in the diversified rotation under both tillage intensities than when spring wheat alternated with GM in the simplified rotation, especially under high tillage. In forage pea, H' was higher than in spring wheat, but did not differ among tillage–rotation systems. The range of fungal species in all crops was similar to that observed in nonorganic crops.Yearly weather differences affected disease severity and prevalence of fungi.Low tillage, diversified rotation had less root rot but higher Fusarium levels in wheat.Shannon diversity index in wheat was higher in diversified than simplified rotations.Some of the fungi in the diversified rotations in wheat had biocontrol capabilities.