Characterization of Seiridium spp. Associated with Cypress Canker Based on ß-Tubulin and Histone Sequences

Abstract

Cypress canker is a serious disease that has devastated Cupressus spp. in many parts of the world. In Mediterranean Europe it has caused the deaths of millions of trees. Three species of Seiridium, S. cardinale, S. cupressi, and S. unicorne, are associated with cypress canker. Considerable debate surrounds the taxonomic status of these fungi. They have been viewed as a single morphologically variable species, three distinct taxa; or two species based on the presence or absence of conidial appendages. Studies based on ribosomal DNA (ITS1, ITS2, and 5.8S gene) sequence failed to separate the cypress canker fungi. In an attempt to distinguish between the species associated with cypress canker we used histone and partial ß-tubulin sequences of fourteen isolates of Seiridium spp. from cypress. Analysis of sequence data showed Seiridium isolates from Cupressus spp., residing in two major clades. One clade accommodated S. unicorne isolates from Portugal and South Africa. The other major clade consisted of two subclades containing non-appendaged S. cardinale isolates. We believe the larger second clade, represents the cypress canker pathogens while the other clade contains the less pathogenic S. unicorne, which has a host range beyond Cupressus. This study thus provides strong evidence to support previous morphological data suggesting three distinct species are associated with cypress canker.

Keywords: phylogeny.