Occurrence of Phytophthora macrochlamydospora in New South Wales and its pathogenicity to some legume species
Herbarium material of a Phytophthora species recorded on soybeans in New South Wales during 1985 was re-examined and identified as P. macrochlamydospora Irwin. A range of soybean cultivars and some legumes that occur naturally on the north coast region of New South Wales were tested for their reaction to artificial inoculation with P. macrochlamydospora. On soybeans, variable reactions were recorded indicating resistance in some cultivars. A number of the legumes were susceptible to infection. P. macrochlamydospora appears to be endemic on the north coast of New South Wales but has not been recorded from other areas of New South Wales.
The prevalence and severity of diseases in the coastal soybean crop of New South Wales
Rainfed soybean (Glycine max) crops in the northern coastal region of New South Wales were surveyed from 1985 to 1987 for the prevalence and severity of diseases. Sixteen diseases were recorded over the 3 seasons, but only rust (Phakopsora pachyrhizi), black leaf blight (Arkoola nigra) and bacterial pustule (Xanthomonas campestris pv. glycines) were present each season. Rust was the most significant disease, infecting 50, 20 and 6% of crops in 1985, 1986 and 1987. The severity of rust was related to rainfall and temperature after flowering, with the most severe outbreaks in the higher rainfall area of the lower Richmond Valley. Black leaf blight was also significant and occurred in 39, 10 and 27% of crops in 1985, 1986 and 1987, but in most crops severity was low. The other diseases recorded were downy mildew (Peronospora manschurica), root and stem rot (Phytophthora megasperma f. sp. glycinea), stem canker (Rhizoctonia sp.), pod and stem blight (Phomopsis spp.), anthracnose (Colletotrichum spp.), seedling blight (Rhizoctonia sp.), stem rot (Phytophthora sp.), white mould (Sclerotinia sclerotiorum), flower blight (Botrytis cinerea), leaf spot (Phoma sp.), bacterial blight (Pseudomonas syringae pv. glycinea), mosaic (soybean mosaic virus) and orange bark (not identified). All of these diseases were generally of low prevalence and severity.
Spatial distribution of root lesion nematodes (Pratylenchus spp.) in a long-term no-till cropping system and their relationship with soil and landscape properties
The Cook Agronomy Farm of Washington State University is a long-term precision agriculture study site. Since 2000, the farm has been in various three-year no-till rotations with winter wheat, spring wheat, and various rotation crops such as barley, canola, peas, lentils, and chickpea. The spatial distribution of root lesion nematodes (Pratylenchus spp.) and their relationships with soil and terrain variables were studied by collecting soil samples at 127 and 124 geo-referenced points in two 12-ha fields during the spring of 2010 and 2011, respectively. Pratylenchus spp. were detected in more than 85% of the sampled locations in both fields. Nematode densities spatially mapped using ArcGIS software occurred in an aggregated pattern. Previous rotation crops had no effect on the spatial distribution. Classification and regression tree analysis (CART) using soil and terrain variables, and nematode density, explained 61 and 34% of the variability associated with nematode density in 2010 and 2011, respectively. Soil edaphic factors, such as organic matter, were stronger predictors of nematode populations than rotation effects.