The impact of anecic earthworms on the dispersal of Microdochium nivale in amenity sports turf

Abstract

In sports surface management, integrated disease management (IDM) is useful in identifying the parameters for which disease can occur. The host, pathogen and environment are factors that are intrinsically linked for disease to manifest. When either of these causal components is not present then plant disease is prevented. Soil biotas have been implicated in the movement of pathogenic soil microbes through both consumption and ejection and by external contamination, the propagule attaching itself to the external wall of the earthworm. Soil biota could therefore be included as a causal factor in disease development. The aim of this thesis was to investigate the impact anecic earthworms have on the dissemination of Microdochium nivale in amenity sports turf. An initial experiment to ascertain viability of M. nivale spores post ingestion through Lumbricus terrestris was performed. Sterilised soil pre-inoculated with M. nivale was fed to earthworms and propagules re-isolated from the faecal matter using a soil dilution technique. Results showed that 10% of viable propagules of M. nivale fed to earthworms survived the digestion process and were evident in the faecal matter (cast). A turf microcosm experiment was established to record whether the casts containing propagules of M. nivale could lead to infections of Fusarium patch, the plant disease caused by M. nivale in amenity turf. Spiked casts (M. nivale) were placed in pots containing Lolium perenne and the incidence and severity of disease was recorded using image analysis. The conclusions were that the spiked cast material was no more infectious than spore solutions of M. nivale inoculated onto the plant material. A final investigation of the effects the presence and absence of earthworms have on the dissemination of M. nivale propagules in turf grass was conducted. Turf microcosms containing Agrostis stolonifera were pre-inoculated with a spore solution of M. nivale in either the presence or absence of earthworms. Rate and progression of disease was recorded using image analysis, dispersal of propagules was assayed through leaf sampling in the microcosm. Results indicated that the presence of earthworms had a greater effect on both the manifestation of Fusarium patch, and the dispersal of M. nivale propagules than in the absence of earthworms. This study has provided a contribution to understanding the interactions between L. terrestris and M. nivale. It is clear that earthworm interaction with M. nivale enhances the dispersal of viable propagules, potentially leading to fresh manifestation of disease. Recommendations regarding the management of terrestris, already considered a nuisance on fine turf due to its casting; would be to mitigate these earthworms in areas of intensively managed turf, whereby the advantages of high earthworm activity are neither necessary nor required.