STIGMINA BARK CANKER OF APPLE

Abstract

Stigmina pallida (Ellis & Everhart) M. B. Ellis incited a bark disease of apple characterized by cankers and discoloration of underlying wood of 1- and 2-year-old shoots. It differed in spore size and cultural characteristics from S. negundinis (Berk. & Curt.) M. B. Ellis, a pathogen of box elder with which it had been considered to be cospecific. S. pallida had larger spores (36–44–50 × 14–17–20 μ) than those of S. negundinis (30–36–40 × 11–15–19 μ) and grew in agar culture at a slower rate over a narrower range of temperature. S. pallida was pathogenic to apple and smooth sumac but not to box elder, while S. negundinis was pathogenic to box elder and smooth sumac but not to apple.