Sirococcus blight: a seed-borne disease of container-grown spruce seedlings in Coastal British Columbia forest nurseries

Abstract

Sirococcus blight, caused by Sirococcus strobilinus Preuss, was shown to be a seed-borne disease of container-grown Picea sitchensis (Bong.) Carr., P. glauca (Moench) Voss, P. engelmannii Parry, and P. glauca × P. engelmannii spruces. The fungus was best detected by germinating seeds from seedlots with consistent disease histories, in autoclaved soil mix in pots (kept at 16 to 20 °C, and at light intensities of 900 to 1800 lx), and isolating the pathogen from diseased seedlings. Seed-borne isolates of S. strobilinus were pathogenic to P. sitchensis seedlings. The pathogen was present on 0.3 to 3.1% of the seeds of infested seedlots. Seeds with shrunken contents yielded the pathogen seven to nine times more often than seeds with normal-appearing contents. Disease incidence was unrelated to seedcoat damage or prevalence of empty seeds. Histological examinations revealed presence of the pathogen throughout the endosperm and embryo tissues of diseased seeds. The results are discussed in relation to incidence of Sirococcus blight in Coastal, container nurseries.