PYRICULARIA LEAF-SPOT - A NEW DISEASE OF ORNAMENTAL PLANTS OF THE FAMILY MARANTACEAE

A severe leaf spot disease incited by the fungus Pyricularia oryzae wa s identified on Ctenanthe oppenheimiana and C. setosa ''Greystar.'' Pr imary symptoms on young leaves consisted of individual circular to sli ghtly irregular pinpoint spots with white necrotic centers zonated by narrow brown-yellow halos. On mature leaves, extended necrotic areas r esembling those caused by phytotoxicity were formed. Artificially inoc ulated leaves with a spore suspension of the isolated fungus from the above case showed symptoms after 3 to 4 days' incubation at 25 degrees C and high humidity. Fungal isolates obtained from Ctenanthe plants o f Brazilian origin were found to be highly pathogenic on various plant s within the family Marantaceae when they were tested by an excised le af assay method. By contrast, P. oryzae isolates obtained from rice pl ants grown in Greece caused either hypersensitivity or immune response symptoms in various Marantaceae. Analysis of esterase and lactate deh ydrogenase isozymes showed different banding patterns for rice and Cte nanthe isolates of P. oryzae. Conditions of prolonged leaf wetness com bined with prevailing high temperature and humidity favored the epidem ic appearance of the Pyricularia leaf spot disease on glasshouse-grown plants during the summer months of 1995 in Greece.