Host effect on genetic variation of Marssonina brunnea pathogenic to poplars

A bread collection was made for 42 isolates of Marssonina brunnea affecting poplar trees from three different sections (Leuce, Aigeiros and Tacamahaca ) within the same Populus genus in China. Genetic diversity among these iso lates was analyzed for morphological traits, cultural features, pathogenici ty, hyphal anastomosis and randomly amplified polymorphic DNA markers (RAPD s). No significant difference was found in conidial morphological features, such as size, shape and septum location. Yet, considerable differences occ ur in other characteristics, which leads to the classification of the 42 is olates into two distinct groups, M. brunnea f.sp. monogermtubi and M. brunn ea f.sp. multigermtubi. Isolates of M. brunnea f.sp. monogermtubi, derived from section Leuce, germinate only one germ tube, grow fast, produce dark-r eddish conidiosorus clusters on the PDA medium, and are highly pathogenic t o Populus tomentosa of section Leuce. By contrast, isolates of M. brunnea f .sp. multigermtubi, derived from sections Aigeiros and Tacamahaca, germinat e 1-5 germ tubes, grow slowly, produce yellow-greenish conidiosorus cluster s on PDA medium, and are pathogenic to Populusxeuramericana cv I-45 and Pop ulus canadensis of section Aigeiros. DNA amplification using II RAPD primer s generate 78 polymorphic bands among isolates. Cluster analyses based on R APD markers broadly support such a classification by phenotypes, but provid e a new insight into the possible origins of ill. brunnea. It is proposed t hat the pathogen co-evolves with the poplars of section Leuce and has been subsequently distributed to the poplars of sections Aigeiros and Tacamahaca . An isolate from Populus adenopoda of section Leuce is placed in the third group, which is most likely a transmission type from M. brunnea f.sp. mono germtubi to hi. brunnea f.sp. multigermtubi.