Towards bio-control using Myxomycetes: predatory activity of the myxomycetes Physarum polycephalum and P. pusillum against mycotoxigenic fungi

Some slime mold species are fungivorous, e.g. Badhamia utricularis, and some of them produce antimicrobial, respectively antifungal substances, e.g. as shown for plasmodial extracts against Fusarium oxysporum. Therefore they hold the potential to be used in biocontrol, especially as antagonists to fungal plant pathogens. In our experiments a laboratory strain of Physarum polycephalum (Carolina®) and wild isolates of P. pusillum collected from maize plants on an agricultural experimental field in Austria were used in confrontation-tests against spores and mycelia of mycotoxigenic fungi belonging to the genera Fusarium, Aspergillus, Penicillium and Alternaria. We further tried to investigate whether the glycocalyx of the two myxomycete species has any inhibitory effect on the germination of the fungal spores by placing the spores directly on the glycocalyx. P. polycephalum only takes up spores from some Aspergillus spp. but not from the other genera. In contrast, P. pusillum was less selective and was feeding on spores from all 20 fungal species tested across all four genera. Especially in the plasmodial feeding front, ingested spores could be observed in higher densities. The conidia were enclosed in food vacuoles inside the plasmodium. Except in the case of the recalcitrant, thick walled spores of Alternaria spp. no evidence of spore debris in the glycocalyx was found. This suggests that the spores of e.g. Fusarium were completely digested. We could not observe that P. polycephalum digests mycelium of any of the tested fungal species. On the other hand, P. pusillum was feeding on the mycelium from species of the genera Fusarium, Aspergillus and Alternaria, but not from Penicillium. Time-lapse imaging showed that prior to feeding, the plasmodia partly crawled over aerial mycelium threads, thereafter it was externally solubilized. The glycocalyx of P. polycephalum showed no evidence of inhibiting the germination of the tested fungal spores, whereas the glycocalyx of P. pusillum showed a delay in germination of some Fusarium and Aspergillus species and Penicillium expansum. The obtained results underline the potential of myxomycetes, especially of adapted wild forms as P. pusillum, as antagonists against mycotoxigenic fungi with special refer to fungal plant pathogens.

Publication year:2017