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Pyricularia Leaf Spot: A New Disease of Ornamental Plants of the Family Marantaceae

A severe leaf spot disease incited by the fungus Pyricularia oryzae was identified on Ctenanthe oppenheimiana and C. setosa “Greystar.” Primary symptoms on young leaves consisted of individual circular to slightly irregular pinpoint spots with white necrotic centers zonated by narrow brown-yellow halos. On mature leaves, extended necrotic areas resembling those caused by phytotoxicity were formed. Artificially inoculated leaves with a spore suspension of the isolated fungus from the above case showed symptoms after 3 to 4 days' incubation at 25°C and high humidity. Fungal isolates obtained from Ctenanthe plants of Brazilian origin were found to be highly pathogenic on various plants within the family Marantaceae when they were tested by an excised leaf assay method. By contrast, P. oryzae isolates obtained from rice plants grown in Greece caused either hypersensitivity or immune response symptoms in various Marantaceae. Analysis of esterase and lactate dehydrogenase isozymes showed different banding patterns for rice and Ctenanthe isolates of P. oryzae. Conditions of prolonged leaf wetness combined with prevailing high temperature and humidity favored the epidemic appearance of the Pyricularia leaf spot disease on glasshouse-grown plants during the summer months of 1995 in Greece.