The pathogenicity of isolates of Endothia gyrosa to Eucalyptus nitens and E-globulus

A severe epidemic of Endothia gyrosa in a plantation of Eucalyptus nitens a t Tewkesbury in Tasmania prompted a comparison of the pathogenicity of isol ates from this site with that of isolates from elsewhere in Tasmania and ma inland Australia. Sixteen isolates were artificially inoculated on 12-month -old seedlings of two major plantation species, E. nitens and E. globulus. The majority of isolates produced lesions on both host species that were si gnificantly different in size to those in non-inoculated seedlings and were not callused-over at 7 months after inoculation. Seedling mortality was ne gligible. Certain isolates originating from various regions in mainland Aus tralia and from the Tewkesbury site appeared more pathogenic although diffe rences in lesion size between isolates was not always significant. Only one out of seven isolates from Tewkesbury demonstrated significantly higher le vels of pathogenicity than all other isolates although there was a trend fo r isolates from this site to cause greater lesions in size. It is, however, unlikely that the epidemic caused by E. gyrosa at Tewkesbury, even though of far greater impact than previously observed on plantations in Australia, is solely the consequence of more pathogenic strains. This conclusion does not exclude the possibility that more pathogenic strains of an opportunist pathogen such as E. gyrosa could have played some determinant role in epid emic development.