Penetration of Sitka spruce seeds by the pathogenic fungus Caloscypha fulgens

Abstract

Penetration of Sitka spruce, Picea sitchensis (Bong.) Carr., seeds by the pathogenic fungus Caloscypha fulgens (Pers.) Boudier was examined in intact and sectioned naturally infected and inoculated seeds with light and scanning electron microscopes. One to seven circular to slightly elongate, white to whitish blue infection cushions occurred on a typical naturally infected seed. Within 1–3 days following inoculation, the fungus formed dome-shaped infection cushions on the seed surface and within the next 10 days several straight-line penetration holes were observed in the seed coat directly under each cushion. During penetration, pathogen growth was confined to the penetration holes and intertissue spaces until it reached the endosperm and embryo tissues throughout which it ramified. Caloscypha fulgens occasionally entered seeds through seed coat cracks, but never through the micropyle. Pathogen emergence from diseased seeds occurred through intact or cracked seed coats and the micropyle.