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United States Department of Agriculture

Agricultural Research Service

Title: Plectosporium Alismatis Comb. NOV., a New Placement for the Alismataceae Pathogen Rhynchosporium Alismatis

Authors
item Pitt, Wayne - CHARLES STURT UNIV, AUSTR
item Goodwin, Stephen
item Ash, Gavin - CHARLES STURT UNIV, AUSTR
item Cother, N - NEW SOUTH WALES AG, AUSR
item Cother, Eric - NEW SOUTH WALES AG, AUSTR

Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 2004
Publication Date: June 30, 2004
Citation: Pitt, W.M., Goodwin, S.B., Ash, G.J., Cother, N.J., Cother, E.J. 2004. Plectosporium alismatis comb. nov., a new placement for the alismataceae pathogen rhynchosporium alismatis. Mycological Research. 108(7):775-780.

Interpretive Summary: Many plant pathogenic fungi have potential to be used as biological control agents for weeds. However, development of a potential biocontrol agent requires thorough knowledge about its host range and evolutionary relationships. The plant pathogenic fungus, Rhynchosporium alismatis, infects several genera of plants in the family Alismataceae and is under investigation currently as a mycoherbicide for aquatic weeds in Australian rice crops. To date, the placement of R. alismatis within the genus Rhynchosporium remains controversial and almost nothing is known about the evolutionary relationships of this species relative to other members of the genus. To test whether R. alismatis belongs in the genus Rhynchosporium and to identify other related fungi, the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1, 5.8S rRNA gene, ITS2) was sequenced and compared to sequences available in databases. Analysis of 73 ITS sequences revealed close relationships between R. alismatis and the fungal genus Plectosphaerella, as well as several asexual fungi which were primarily species of Verticillium. These species are all members of the order Phyllachorales, distinct from the other members of the genus Rhynchosporium. Therefore, R. alismatis clearly is not related to other members of the genus Rhynchosporium and instead should be moved into the genus Plectosporium (the name for the asexual stage of Plectosphaerella). This clears up a controversy that has existed since R. alismatis was first named in 1922. These results will be useful to plant pathologists and evolutionary biologists. It also is essential information for weed scientists that hopefully will speed the development of R. alismatis into a biological control agent for aquatic weeds of rice crops.

Technical Abstract: The phytopathogenic fungus Rhynchosporium alismatis infects Alisma, Sagittaria and other genera in the Alismataceae and is under investigation currently as a mycoherbicide for alismataceous weeds in Australian rice crops. To date, the placement of R. alismatis within the genus Rhynchosporium remains controversial and almost nothing is known about the phylogenetic relationships of this species relative to other members of the genus. To establish these associations and identify fungi which may be related to R. alismatis, the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1, 5.8S rRNA gene, ITS2) was sequenced and compared to sequences available in databases. Analysis of 73 ITS sequences revealed close relationships between R. alismatis and the teleomorph genus Plectosphaerella, as well as several anamorphic fungi which were primarily species of Verticillium. Rhynchosporium alismatis and P. cucumerina clustered together with 98% bootstrap support, demonstrating that both are members of the Phyllachorales, distinct from R. secalis and R. orthosporum which clustered monophyletically with members of the Helotiales. Rhynchosporium alismatis clearly is not related to other members of the genus Rhynchosporium and instead should be moved into the genus Plectosporium.

Last Modified: 10/1/2014
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