Burgess, T.I., 2013. Phytophthora arenaria. Forest Phytophthoras 3(1). doi:10.5399/osu/fp.3.1.3391
Phytophthora arenaria
Overview
Phytophthora arenaria A. Rea, M. Stukely & T. Jung, has been isolated in Western Australia from kwongan heathland stands since the early 1980s (Burgess et al. 2009, Rea et al. 2011), but was misidentified as P. citricola. Phytophthora arenaria has been isolated exclusively from the northern sand plains and was named based on its association with sandy soils. Most isolates were associated with dead or dying Banksia spp. (Proteaceae). When active, symptomatic plants are scattered in the landscape. However, the overall impact of this species within the natural environment is low due to the low rainfall in the region and the sporadic nature of the disease.
Morphology
Sporangia non-caducous, papillate, occasionally bipapillate, tripapillate and bilobed; ovoid, broadly ovoid, elongated ovoid, obpyriform or asymmetrically mouse-shaped, and showing conspicuous basal plugs (31.8 ± 4.6 mm x 23.7 ± 3.5 mm). Sporangiophores generally terminal, occasionally lateral. Proliferation absent. Hyphal swellings catenulate, globose to sub-globose, some with radiating hyphae. Chlamydospores absent. Homothallic having oogonia with slightly wavy walls turning dark-brown to bronze-brown with maturity, antheridia exclusively paragynous, oospores markedly aplerotic with thick walls [24.3 to 28.1 mm (av. 25.3)]. Oospore wall index 0.50 ± 0.05.
Genetics
Phytophthora arenaria resides in ITS clade 4 with the most closely related species being P. alticola (Maseko et al. 2007). It differs from P. alticola by 3, 2, 6, 3 and 21 SNPs in ITS BT, HSP, enolase and cox I gene regions, respectively.
Growth
It grows on CA agar at 15-32.5°C with an optimum near 30°C (radial growth rate 6.5 ± 0.49 mm d-1). No growth occurs at 10 or 35°C, but neither temperature was lethal. P. arenaria produces smooth, radiate to faintly stellate colonies on CA, V8A, MEA, ½PDA.
Distinguishing Characteristics for Identification
P. arenaria is distinguished from the most closely related species, P. alticola, by having exclusively paragynous antheridia and mature oogonia with wavy margins.
Disease History
Phytophthora arenaria has been isolated almost exclusively from Banksia-dominated heathlands in Western Australia. Most isolates were associated with dead or dying Banksia spp. (Proteaceae) scattered in the landscape. Original isolations were initially misidentified as P. citricola based on morphology alone. However, during the re-evaluation of Phytophthora species isolated during 30 years of vegetation health surveys in Western Australia using molecular techniques, several new species were identified with these isolates initially being called P. sp. 1 (Burgess et al., 2009) which were later described as the new species P. arenaria (Rea et al. 2010). Since the original description many more isolates have had their identities verified and to date there are now 49 individual records of this species. Most interestingly, all new isolates are from the dry northern sand plains and while many other species (including new species) have been isolated during recent surveys in the urban landscape (Barber et al, 2013), P. arenaria has been exclusively isolated from natural vegetation. To date, P. arenaria has not been reported outside of Western Australia.
Impacts in the Forest
The impact of this species within the natural environment is low due to the low rainfall in the region and the sporadic nature of the disease.
Forest and Wildland Hosts and Symptoms
Disease symptoms are limited to the sporadic sudden death of individual Banksia plants (a small to medium shrub which dominates the sand plains of Western Australia) often associated with a basal canker, collar rot, and dieback.
| Host Latin Name | Host Common Name | Symptoms | Habitat | Region |
|---|---|---|---|---|
| Banksia spp. | Banksia Canker | Collar rot, Dieback | Wildland | Australia - Western |