A canker and foliage disease of yellow birch. II. Artificial infection studies with Diaporthe alleghaniensis

Abstract

Disease symptoms found in nature on yellow birch (Betula alleghaniensis Britt.) infected by Diaporthe alleghaniensis R. H. Arnold, were induced by inoculation of seedlings and saplings with mycelium or conidia. On vigorously growing yellow birch plants, cankers, dead shoots, blackened necrotic petioles and mid-veins of leaves, and leaf spot developed during the inoculation year, and dieback occurred the next spring. Spore tendrils of the Phomopsis state of the pathogen were found on the most recently killed parts of the plants from May until early July. Initial symptoms were most severe on young tissues, and inoculation of shoots caused more damage to seedlings than inoculation of older tissues. The pathogen persisted in the host for several years without symptom expression, or in healed-over cankers. Initial symptoms were more severe on unshaded than on shaded seedlings, but shading increased the ultimate severity of the disease. Soil temperature and soil moisture did not influence artificial infection and subsequent development of the disease. There was evidence that the fungus produces a wilt-inducing agent. The disease was not found in nature on white birch (Betula papyrifera Marsh.), but seedlings were infected artificially. The probable course and importance of natural infection of yellow birch is discussed.