Use of remote sensing to map occurrence and spread of Phytophthora cinnamomi in Banksia woodlands on the Gnangara Groundwater System, Western Australia

The soilborne plant pathogen Phytophthora cinnamomi is listed as one of the world’s 100 worst invasive alien species by the International Union for Conservation of Nature (IUCN). The impacts on native flora and fauna habitats have been identified as a key threatening process in Australia. Identifying and mapping diseased vegetation and the rate of spread of the disease is required for management; however, this is often difficult and costly. This study investigated the ability of using a time series of orthophotos (1953–2008) in combination with Landsat satellite imagery, including trend analysis, and GIS to identify the presence of vegetation impacted by P. cinnamomi at four sites in Banksia woodlands in Western Australia. Further, the historical extent and rate of spread of P. cinnamomi was assessed at one site between 1953 and 2008. Our assessment identified that three of the four sites were affected by P. cinnamomi, results that are consistent with on-ground surveys. Investigation of disease progression at one site found a large increase in the area impacted between 1974 and 1988 and the rate of spread was highest between 1953 and 1963 (1.286 m year−1) and lowest between 1997 and 2008 (0.526 m year−1). The techniques presented provide a cost-effective tool to monitor broad-scale vegetation dynamics over time for management of this plant pathogen.

Ammonia and Nitrous Acid from Nitrogenous Amendments Kill the Microsclerotia of Verticillium dahliae

This study examined the mechanisms by which nitrogenous amendments such as meat and bone meal kill the soilborne plant pathogen Verticillium dahliae. The effect of nitrogen products from the amendments on the survival of microsclerotia of V. dahliae was examined by solution bioassay and soil microcosm experiments. Ammonia and nitrous acid but not their ionized counterparts, ammonium and nitrite, were toxic to microsclerotia in bioassays. In microcosms, addition of meat and bone meal (2.5%) to an acidic loamy sand resulted in the accumulation of ammonia and death of microsclerotia within 2 weeks. At lower concentrations (0.5 and 1%), microsclerotia were killed after 2 weeks when nitrous acid accumulated (>0.03 mM). In an alkaline loam soil, microsclerotia survived at 3% meat and bone meal and neither ammonia nor nitrous acid accumulated. The toxicity of ammonia to the pathogen was verified by increasing the concentration of meat and bone meal to 4% or addition of urea (1,600 mg of N per kg) to the loam soil resulting in the accumulation of ammonia (>35 mM) and death of microsclerotia. The toxicity of nitrous acid was verified by adding ammonium sulfate fertilizer to an acidic sand soil. Inhibiting nitrification with dicyandiamide revealed that nitrous acid was generated as a result of the accumulation of nitrite and an acidic pH. Thus, levels to which the toxins accumulated and the effective concentration of amendment were dependent upon the soil examined. Of the two mechanisms identified, accumulation of nitrous acid is the more promising strategy to control plant diseases in acidic soil because it is more toxic than ammonia and is formed at lower concentrations of amendments.

Chloride requirement for reproduction by Pythium ultimum

Chloride (≥ 0.1 mM) was essential for asexual and sexual reproduction, but not mycelial growth, by Pythium ultimum in synthetic culture media. Bromide partially substituted for chloride in support of oogonia formation. The production of gemmae (sporangia or hyphal swellings) increased in proportion to concentrations of KCl in culture media between 0.2 and about 0.5 mM but leveled off between 0.5 and 4 mM. Chloride contents of mycelia after 3 days incubation were proportional to the number of gemmae produced when the fungus was grown in low concentrations of KCl. Under the culture conditions of this study, production of oogonia and gemmae commenced in about 70 and 95 h, respectively, in complete media. When 0.2 mM KCl was added to cultures 95 h or older that were grown in chloride deficient media, oogonium or gemma production was initiated in 20–25 or 10–17 h, respectively. Germination of gemmae, mycelial growth (gain in dry matter), and culture pH were not influenced significantly by the chloride deficiences that prevented sexual and asexual reproduction.Key words: chloride requirement, soilborne plant pathogen, reproduction of fungi, sporangia, hyphal swellings.