Dendryphion penicillatum and Pleospora papaveracea, destructive seedborne pathogens and potential mycoherbicides for Papaver somniferum

Dendryphion penicillatum and Pleospora papaveracea were isolated from bligh ted Papaver somniferum and Papaver bracteatum plants grown in growth chambe rs and the field in Beltsville, MD. The etiology of the diseases was determ ined, and the fungi are being investigated as potential mycoherbicides to c ontrol the narcotic opium poppy plant. P. papaveracea is known to be a high ly destructive seedborne pathogen of Papaver somniferum, causing seedling b light, leaf blight, crown rot, and capsule rot. Single conidia and ascospor es were isolated and cultures established from naturally infested seed and diseased foliage and pods of opium poppy from Iran, Colombia, Venezuela, Sw eden, India, and the United States (Maryland and Washington). Mycelia and c onidia of P. papaveracea and D. penicillatum produced on necrotic leaf tiss ues appear morphologically similar, and the fungi were previously considere d to be anamorph and teleomorph. However, no anamorph/teleomorph connection could be established, and the fungi appear to be distinct taxa. P. papaver acea produced conidia, mature pseudothecia, and chlamydospores in vitro and on infected stems. D. penicillatum produced conidia, microsclerotia, and m acronematous conidiophores. Although both fungi were pathogenic to three po ppy cultivars, conidial inoculum from P. papaveracea cultures was more viru lent than conidial inoculum from D. penicillatum. Eight week-old plants bec ame necrotic and died 8 days after inoculation with a conidial suspension o f P. papaveracea at 2 x 10(5) spores per mi. Disease severity was significa ntly enhanced by inoculum formulations that contained corn oil, by higher c onidial inoculum concentrations, and by increased wetness periods. Symptoms on plants inoculated with either pathogen included leaf and stem necrosis, stem girdling, stunting, necrotic leaf spots, and foliar and pod blight. I noculated seedlings exhibited wire stem, damping-off, and root rot. Conidia , and less frequently pseudothecia, of P. papaveracea and conidia of D. pen icillatum were produced abundantly on inoculated, necrotic foliage, pods, a nd seedlings. Cultures from conidia or ascospores reisolated from these tis sues consistently produced fungi whose morphologies were typical of the fun gus from which the inoculum was derived.