Phylogenetic and developmental evidence supporting reclassification of cruciferous pathogens Phoma lingam and Phoma wasabiae in Plenodomus

To evaluate the classification of Phoma lingam (Tode:Fr.) Desm. and Phoma wasabiae Yokogi in the genus Phoma, a phylogenetic study of Phoma spp. was conducted using ribosomal DNA internal transcribed spacer 1 sequences. The majority of the Phoma species included in the study clustered in a Phoma-Didymella clade (Venturiaceae). Phoma lingam and P. wasabiae consistently clustered outside of the Phoma-Didymella clade, instead forming the Plenodomus clade (Leptosphaeriaceae). This result supports classification of P. lingam and P. wasabiae in Plenodomus as has been proposed by earlier investigators. Features of the morphology and development of pycnidia of Phoma americana Morgan-Jones & White and P. lingam suggest that Phoma and Plenodomus may also be distinguishable morphologically. Our results suggest that difficulties of identification and classification in Phoma may be resolved by using a phylogenetic approach to classification.Key words: Coelomycetes, molecular systematics, pathogens, taxonomy.