Two strains of Alternaria alternata were tested for their conditions of sporulation and invasion to the host. The best sporulation was obtained when pathogen spores were incubated on leaf surface of tobacco seedling, and the worst on distilled water. The pathogenicity of pathogen was enhanced by washing leaf surface with acetone and 700% alcohol and by exposing the seedlings out of green-house. Three methods of inoculation were tested and droplet inoculation gave the most serious symptom. The components and...