Etiology of apple sooty blotch disease in north Carolina

ABSTRACT Sooty blotch disease of apples (Malus x domestica), previously attributed to the fungus Gloeodes pomigena, was shown to be a disease complex caused by fungi previously considered mycelial types of G. pomigena. Peltaster fructicola and Geastrumia polystigmatis were associated with the ramose mycelial type. A fungus similar to P. fructicola, but with smaller pycnothyria and conidia, was associated with the punctate mycelial type. The diffuse fuliginous mycelial type was caused by Leptodontium elatius. Fungi that fit the classical morphological description of G. pomigena were not observed. Pycnothyria of P. fructicola developed on overwintered colonies on blackberries, and conidia were a source for primary infection during the entire growing season. Secondary spread was through conidia produced in colonies on fruit. L. elatius was observed infrequently producing conidia on fruit during periods of extended high moisture. Histological examination did not reveal penetration of the cuticle of apple fruit for any of the fungi of the apple sooty blotch complex.