Comparative Morphology and Pathology of Calonectria theae and C. colhounii in Hawaii

Calonectria theae is distinguished from C. colhounii by perithecial color, number of ascospores in an ascus, longer stipes, longer conidia, and the formation of a second conidial type that is extraordinarily long, angular, and borne on simple, submerged, dichotomously branching conidiophores. Both species were isolated from ohia (Metrosideros collinus), M. excelsus, and sentry palm (Howea forsteriana). C. theae was also isolated from leather leaf fern (Rumohra adiantiformis) and Strelitzia, while C. colhounii isolates were obtained from Eucalyptus, Leucospermum, and Chrysalidocarpus lutescens. All tested isolates of both Calonectria spp. were pathogenic to ohia, an important native tree species in Hawaiian forests. Both species killed apical shoots, and caused leaf spotting, blighting, and subsequent defoliation. Symptomatically, the diseases caused by these species are indistinguishable on ohia. This disease poses a potential threat to native forests.