R. A. Skipp

Influence of nematophagous fungi, earthworms and dung burial on development of the free-living stages of Ostertagia (Teladorsagia) circumcincta in New Zealand

Biological options for nematode parasite control are being sought, as the long-term efficacy of conventional anthelmintics comes increasingly under threat from drug-resistant parasites. Three biological methods with the potential to reduce pasture contamination by parasitic nematode larvae were examined: (a) killing of larvae developing in dung by nematophagous fungi; (b) removal of dung through earthworm ingestion; (c) burial of dung in soil as might occur through the action of dung beetles. Field trials with the test bio-control agents were carried out in autumn and spring by adding dung from sheep infected with Ostertagia (Teladorsagia) circumcincta to pots of ryegrass/white clover. The factorial treatment structure included five fungal treatments (individual applications of Duddingtonia flagrans, Monacrosporium gephyropagum and Harposporium helicoides, a combination of all the three fungi together and an untreated control), two dung burial treatments (dung buried or deposited on the soil surface) and two earthworm treatments (earthworms present or absent). D. flagrans and H. helicoides, individually or in combination, reduced recovery of infective stage larvae in experiment 1, while only H. helicoides reduced recovery in experiment 2. In both the experiments, dung burial increased the total number of larvae recovered, while the number of infective larvae were reduced by the action of earthworms. Increased recovery following burial, along with the fact that larvae moved rapidly from soil onto herbage, suggests that soil may provide a protective reservoir for infective larvae infesting herbage.

Occurrence, morphological characteristics and ribotyping of New Zealand isolates of Duddingtonia flagrans, a candidate for biocontrol of animal parasitic nematodes

Abstract The nematophagous fungus Duddingtonia flagrans has shown potential for biological control of nematode parasites of livestock in several countries. A survey for the presence of D. flagrans in New Zealand was undertaken in 1997–98 on 24 farm, research, and domestic properties in the southern North Island. The nematophagous fungi found on isolation plates included species of Arthrobotrys, Dactylellina, Nematoctonus, Harposporium, and Duddingtonia. Isolates that produced the three‐dimensional nets and abundant chlamydospores, characteristic of D. flagrans, were detected in 6 of 205 samples examined. The fungus was obtained from a variety of substrates such as cattle dung, horse dung, seepage from a silage pit, and decomposing lawn clippings. Morphological characteristics, and the sequences of ITS/5.8 region of ribosomal DNA, were very similar to those published for D. flagrans. The fungus was re‐isolated from the faeces of lambs 16–40 h after they had been dosed orally with chlamydospores, indicating survival of gut passage.

SAPROPHYTIC GROWTH IN SOIL OF A STRAIN OF TRICHODERMA KONINGII

Abstract A soil‐sandwich bioassay was used to determine the influence of temperature, moisture, form of nitrogen, and the soil microflora on the saprophytic growth through soil of an isolate of Trichoderma koningii. Incubation temperature affected the saprophytic growth of the fungus in soil over the range tested. Saprophytic growth of the isolate in sterile soil increased with incubation temperature from 5°C to the optimum temperature 25°C; there was no saprophytic growth at 30°C. Saprophytic growth also increased with soil moisture content in sterile soil, with a growth optimum at 70% soil water holding capacity (WHC). There was little saprophytic growth at soil moisture contents below 20% WHC. Nitrogen added as ammonium sulphate (NH+4‐N) increased the saprophytic growth of T. koningii in sterile soil whereas nitrogen added as nitrate (NO−3‐N) suppressed growth of T. koningii. Saprophytic growth of T. koningii was markedly reduced in the presence of a natural soil microflora, and enhanced in soil steril...

Verticillium dahliae and other pathogenic fungi in Cirsium arvense from New Zealand pastures: occurrence, pathogenicity and biological control potential

Abstract Cirsium arvense (Californian thistle) populations in pastures throughout New Zealand were surveyed in November–December 2005 (30 sites) and January–March 2006 (94 sites) to identify potential biological control agents for this weed. Fungi were isolated from healthy shoots and shoots showing leaf yellowing/browning, stunting or localized lesions. Verticillium dahliae was isolated most frequently, being detected at 30% of the sites in 2005 and at 51% in 2006. Other pathogenic/saprophytic fungi isolated included Sclerotinia sclerotiorum, Plectosphaerella cucumerina and species of Cylindrocarpon, Rhizoctonia and Phoma. Inoculating cut shoots of C. arvense with conidia of V. dahliae, or cutting shoots with a wetted blade previously used to cut infected shoots resulted in yellowing of leaves and shoot death. Spread of V. dahliae infection among plants facilitated by cutting when wet may explain the reported demise of C. arvense populations mown during rainfall and the fungus may have potential as a bioherbicide.

Microbial pathogens and plant parasitic nematodes in pastures with declining vigour.

Abstract Two years after establishment, areas of low vigour (LV) were noticed within a white clover (Trifolium repens)/ryegrass (Lolium perenne) pasture. These areas became progressively larger, and, two years later, the pasture had low vigour, comprising only 3% white clover. Clover tissue nitrogen and phosphorus levels were greater in high vigour (HV) than in LV herbage. There were no differences (P > 0.05) in “total” bacteria, fluorescent pseudomonads, or proportions of deleterious bacteria in LV and HV white clover roots (mean logio CFUs for total count and fluorescent pseudomonads were 9.4 and 8.8, respectively, and the proportions of deleterious bacteria encountered in these groups were 6.9% and 17.5%). There was a 9‐fold difference (P < 0.01) in the white clover dry matter between LV areas and HV areas in February, increasing to 25‐fold (P< 0.01) in March. The total dry matter yield differences, which included grasses and clover, were 2.7‐ and 2‐fold (P < 0.01) for the two months. More fungi were isolated (P < 0.05) from LV white clover roots than from HV roots (164 and 104 isolates, respectively). This was mostly due to greater numbers (P < 0.01) of Codinaea fertilis in LV roots (111 cf. 41 in HV). In ryegrass roots, there were also greater numbers (P < 0.01) of total fungi in LV roots (97 cf. 50 total isolates in HV), mostly due to higher populations of Fusarium oxysporum in LV roots (29 isolates cf. 5 in HV). There was no difference (P > 0.05) in the Soil Pathogenicity Index between LV and HV soil. The plant parasitic nematode populations in 250 ml of soil in LV and HV areas were 42.7 and 9.7 for Heterodera and 28.1 and 3.9 for Meloidogyne, respectively.

Effects of endophytic and saprophytic fungi on in vitro methanogenesis

Abstract The predominance of pasture in the diet of ruminants in New Zealand presents specific challenges for mitigation of enteric methane emissions. However, there is preliminary evidence from both laboratory and animal-based studies that some fungi may suppress enteric methanogenesis. This study determined the antimethanogenic potential of a range of endophytic (Neotyphodium species) and saprophytic (Geotrichum, Monascus, Mortierella and Penicillium species) fungi. Candidate fungi were selected on the basis of their production of various classes of secondary compounds and screened in an in vitro batch-culture fermentation assay. No strains of endophyte in ryegrass or tall fescue suppressed methanogenesis compared with their endophyte-free controls. The supernatant fractions from three strains of Mortierella wolfii were the most promising fungi identified. They suppressed methanogenesis as effectively as an inhibitor of methanogenesis (bromoethane sulphonate at 30 µmoles/L), without also reducing overall fermentation. These strains should be investigated further by screening fresh cultures grown under contrasting conditions to establish some variation in putative bioactive compounds.