Isolation of Phytophthora lateralis from Chamaecyparis foliage in Taiwan

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Summary Following the discovery in 2008 of Phytophthora lateralis in forest soil under old-growth yellow cedar (Chamaecyparis obtusa var. formosana) in north-east Taiwan, further sampling was undertaken in the same region. Soil, root and symptomatic foliage samples were collected from five separate sites where C. obtusa was the dominant species in cloud forests at ca. 1800–2500 m. Soil and fine root samples were baited with cedar needles; both direct isolation and cedar needle baiting were used on foliage samples. Phytophthora lateralis was obtained from soil at three of the sites, but only from three of the 27 soil samples overall. Only one of 25 root samples yielded the pathogen, and this was associated with infested soil. Three foliage samples with symptoms visible as dark brown to black frond tips also yielded P. lateralis; these came from two different sites. This is the first record of P. lateralis infecting the foliage of C. obtusa. Moreover, when some of the symptomatic Chamaecyparis foliage segments were incubated, sporangia of P. lateralis formed on the necrotic tissues, sometimes in the axils of needle segments. The study provides evidence that P. lateralis has both a soil/root infecting phase and an aerial or foliar infecting phase in Taiwan, which is consistent with its unusual combination of water-dispersed (non-papillate) and aerially dispersed (caducous) sporangia. It also demonstrates the importance of investigating the biology, aetiology and ecological behaviour of Phytophthoras in their native, endemic environments.

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