Natural stem infection of Lawson cypress (Chamaecyparis lawsoniana) caused by Phytophthora ramorum

This is the first report of C. lawsoniana as a natural host of P. ramorum. In November 2010, P. ramorum was isolated from a 4 m long by 60 cm wide aerial phloem lesion on another mature C. lawsoniana in a park near Clydebank, Scotland. There was heavy resinosis at the top of the lesion. Adjacent rhododendrons were also infected with P. ramorum. Ten other large C. lawsoniana at the Clydebank site had dieback and aerial or collar lesions caused by the recently introduced Phytophthora species, P. lateralis (SA Green, CM Brasier and JF Webber, unpublished). Such an overlap between P. ramorum and P. lateralis on C. lawsoniana on the same site is likely to lead to direct physical contact between the two species. Since they are closely related phylogenetically and produce similar fruiting structures (e.g. Brasier et al., 2010), such novel contact could result in their hybridisation (Brasier, 2000). This possibility is under investigation.

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