Magnaporthe poae

Pathogen  Profile  Created by  James  P . Kerns

As a requirement for PP 728, Spring 05
Department of Plant Pathology

Summer patch of Kentucky bluegrass caused by Magnaporthe poae Summer patch of a creeping bentgrass putting green
Summer patch of Kentucky bluegrass caused by Magnaporthe poae. Summer patch of a creeping bentgrass putting green.

Introduction:

Magnaporthe poae causes “summer patch” of Poa species, creeping bentgrass, and fine-leaved fescues.  It is considered one of the most important diseases on turfgrass in North America.  It can decimate Kentucky bluegrass lawns and athletic fields and annual bluegrass putting greens.  The pathogen was first identified in 1984, before which it was an unidentified component of Fusarium blight syndrome.


Host Range and Distribution:

M. poae is pathogenic on Kentucky bluegrass (Poa pratensis), annual bluegrass (Poa annua), and fine-leaf fescues (Festuca spp.).  Traditionally this pathogen is associated with Kentucky bluegrass fairways, athletic fields and home lawns. Magnaporthe is a significant problem on annual bluegrass putting greens in the Northeast U.S as well.  Recently, it has been reported as a pathogen of creeping bentgrass (Agrostis stolonifera) in North Carolina in 2005.  M. poae’s geographic distribution ranges from the New England states to as far south as North Carolina and as far west as Nebraska. 


Isolation:

M. poae is readily isolated from 3-5 mm segments of roots or crowns of infected plants.  The infected root and crowns are dipped in a 1% AgNO3 solution for 30-60 seconds followed by a 5-10 second wash in 5% NaCl solution.  After surface-disinfested segments are rinsed in sterile distilled water and blotted dry they can be plated on Gaeumannomyces-selective media or ½ strength PDA amended with 50 mg /L streptomycin sulfate (see Lanschoot 2001).  M. poae is not readily isolated from soil.

 


Magnaporthe poae grown on 1/2 strength PDA
Mangnaporthe poae on 1/2 strength PDA.




Identification:

M. poae is a heterothallic Ascomycete species and perithecia are rarely observed in nature.  In culture, perithecia are black, globose, and have long cylindrical necks.  The asci inside the perithecia are eight-spored, straight to slightly curved, and have a refractive ring at the apex.  The ascospores at maturity have three septations and the end cells are lighter than the center cells.  M. poae produce runner hyphae on host stems that are brown and infection hyphae can originate from these runner hyphae.  Hyphopodia are dark brown, slightly lobed, and globose, and are typically found on diseased tissues.  Mycelium in culture is hyaline, gray or olive-brown, with thick, dark strands of mycelia radiating from the center of the colony. 

Perithecia of M. poae on creeping bentgrass           Hyphpodia of M. poae                
                Perithecia of M. poae on creeping bentgrass                                                                                 Hyphopodia of M. poae.
                                                                                                                                                                      


Symptoms:

In higher cuts of turf (>1”), gray-green, wilting plants appear in small non-delineated patches.  These patches may progress into circular or irregular-shaped patches up to 30 cm in diameter.  White-banded lesions may be apparent on the leaf blades as well.  On putting green turf, plants turn yellow in small circular patches, which can increase from 5 cm to 30 cm in diameter.

Symptoms of summer patch on Kentucky bluegrass
Symptoms of summer patch on Kentucky bluegrass.
Crown rot of creeping bentgrass associated with M. poae infection 
Crown rot of creeping bentgrass associated with M. poae infection.

 



Ecology and Life Cycle
:

 M. poae is an ectotrophic root-infecting (ERI) fungus that produces hyphae along the surface of roots before penetration occurs.  Saprophytic survival of the ERI fungi, including M. poae, is not well characterized.  Yet, it is not believed that these fungi survive well in soil.  Studies on survival have not been conducted for M. poae, but survival studies on another ERI fungus (G. graminis) have been conducted.  G. graminis is thought to survive on dead plant material that was previously colonized by the pathogen.  This method of survival is hypothesized to be true for all the ERI fungi, including M. poae.  Dissemination of the pathogen occurs when healthy roots come into contact with infected roots or dead roots colonized by the pathogen.  M. poae can grow small distances in soil from colonized dead substrates to infect susceptible host as well.  Ascospores are also produced, but their role in dissemination is not understood. 

Dark runner hyphae of M. poae
Dark "runner" hyphae of M. poae.
Ascospores of M.poae
Ascospores of M. poae.



Links to other sites:

APS Plant Disease Note- First Report of Magnaporthe poae on Creeping Bentgrass in NC

Penn State Cooperative Extention- Managing Summer Patch

Ohio State University Extention Fact Sheet- Summer Patch

University of Illinois Extention- Report on Summer Patch

Kansas State Research and Extention- Summer Patch


 

References:

Landschoot, P.J., A.B. Gould, and B.B. Clarke 1993. Ecology and Epidemiology of Ectotrophic Root-infecting Fungi Associated with Patch Diseases of Turfgrass. Pgs 73-76. In Clarke, B.B, and A.B. Gould (ed.). Turfgrass Patch Diseases Caused by Ectotrophic Root-Infecting Fungi.  APS Press, St. Paul, MN. 

Landschoot, P.J. 1988. Taxonomy and Pathogencity of Ectotrophic Fungi with Phialophora Anamorphs from Turfgrasses.  PhD Dissertation.  University of Rhode Island. 

Landschoot, P.J. 2001. Magnaporthe, pp 67-70. In Singleton L.L., J.D. Mihail, and C.M. Rush (ed.). Methods for Research on Soilborne Phytopathogenic Fungi. APS Press, St. Paul, MN.

Tredway, L.P. 2005. First Report of Summer Patch of Creeping Bentgrass Caused by Magnaporthe poae in North Carolina. Plant Dis. 89:204.


Acknowledgement:

All images courtesy of Lane Tredway, Turfgrass Extention Specialist at NC State University.


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