A new disease of coast live oaks (Quercus agrifolia) in California (US) is associated with Geosmithia pallida and Pseudopityophthorus pubipennis
Since 2012, declining coast live oak (Quercus agrifolia) trees have been observed throughout urban landscapes in the counties of Los Angeles, Orange, Riverside, Santa Barbara, Ventura, and Monterey in California (US). Affected trees showed multiple insect entry holes (0.95 mm diameter), branch dieback, and eventually died. Symptoms also included a wet discoloration around entry holes on the trunk and main branches, followed at first by the production of reddish sap and then of whitish foam (hence the common name of the disease: ‘foamy bark canker disease’). Infested trees can produce a large amount of foamy liquid that can run up to 2 feet (60 cm) down the trunk. Beneath the outer bark phloem and xylem, necrotic tissues could be observed. Recent studies have indicated that this new disease is associated with a bark beetle, Pseudopityophthorus pubipennis (Coleoptera: Scolytidae - Western oak bark beetle) and a fungus, Geosmithia pallida. The bark beetle is not new to the USA, but the fungus is recorded for the first time in the USA. Little information is available on G. pallida, it is noted that this fungus has been shown to inhibit root growth of Lepidium sativum (Brassicaceae) by 25% during laboratory experiments conducted in the Czech Republic and that it appears to have affinities with a range of subcorticolous insects. Other studies have also found that a strain of G. pallida obtained from wilting Ulmus in Italy possessed a cerato-ulmin toxin, the protein involved in Dutch elm disease. More studies are needed to better understand the epidemiology, geographical distribution and potential impacts of this disease on oak trees.
Sources
Čížková D, Šrůtka P, Kolařík M, Kubátová A, Pažoutová S (2005) Assessing the pathogenic effect of Fusarium, Geosmithia and Ophiostoma fungi from broad-leaved trees. Folia Microbiologica 50, 59–62.
INTERNET
University of California. Division of Agriculture and Natural Resources. Pest Alert. Geosmithia pallida and Western oak bark beetle (Pseudopityophthorus pubipennis) causing foamy bark canker disease on coast live oak (Quercus agrifolia) in California. http://ucanr.edu/sites/socaloakpests/files/189274.pdf
Kolařík M, Kubátová A, Pažoutová S, Šrůtka P (2004) Morphological and molecular characterisation of Geosmithia putterillii, G. pallida comb. nov., and G. flava sp. nov., associated with subcorticolous insects. Mycological Research 108, 1053-1069.
Lynch SC, Wang DH, Mayorquin JS, Rugman-Jones PF, Stouthamer R, Eskalen A (2014) First report of Geosmithia pallida causing foamy bark canker, a new disease on coast live oak (Quercus agrifolia), in association with Pseudopityophthorus pubipennis in California. Plant Disease 98(9), p 1276.
Scala A, Comparini C, Tegli S, Scala F (2007) A non-Ophiostoma fungus expresses the gene encoding the hydrophobin cerato-ulmin. Journal of Plant Pathology 89, 233–240.