First Report of Summer Patch of Creeping Bentgrass Caused by Magnaporthe poae in North Carolina
Authors: Tredway L. P. 
Published: May 2007

An unknown disease was observed in June 2002 and 2003 on creeping bentgrass (CRB [Agrostis stolonifera L.]) putting greens at The Country Club of Landfall in Wilmington, NC that were established in 2001 with a 1:1 blend of cvs. A-1 and A-4. Soil pH ranged from 7 to 8 at this location because of poor quality irrigation water. Symptoms appeared in circular patches of 0.3 to 1 m in diameter that exhibited signs of wilt followed by chlorosis and orange foliar dieback. The disease was initially diagnosed as take-all patch caused by Gaeumannomyces graminis (Sacc.) Arx & D. Olivier var. avenae (E.M. Turner) Dennis, based on the observation of necrotic roots and crowns that were colonized with dark, ectotrophic hyphae. However, the historical lack of take-all patch occurrence in this region led to the suspicion that G. graminis var. avenae was not involved. Sections of root and crown tissue were surface disinfested in 0.6% NaOCl for 5 min or 1% AgNO3 for 1 min and 5% NaCl for 30 s. Tissue was plated on SMGGT3 (2) or on potato dextrose agar containing 50 mg L-1 of tetracycline, streptomycin, and chloramphenicol. A fungus resembling Magnaporthe poae Landschoot & Jackson was consistently obtained regardless of isolation method. Teleomorph production was conducted on Sachs agar (4) overlaid with autoclaved wheat (Triticum aestivum L.) stem sections. Seven isolates were plated alone or paired with M. poae tester isolates 73-1 or 73-15 (3) and incubated at room temperature under continuous fluorescent illumination. Six isolates produced perithecia and ascospores typical of M. poae (3) when paired with 73-15 but not when plated alone or paired with 73-1; these isolates are, therefore, M. poae mating type ‘a’. Isolate TAP42 did not produce perithecia and remains unidentified. Cone-Tainers (3.8 × 20 cm) containing calcined clay were seeded with ‘A-4’ CRB (9.7 g cm-2) and inoculated 8 weeks later by placing four M. poae-infested rye (Secale cereale L.) grains below the soil surface. Inoculated Cone-Tainers were placed in growth chambers with 12-h day/night cycles at 30/25°C, 35/25°C, or 40/25°C. Field plots (1 m2) of ‘A-4’ CRB in Jackson Springs, NC were inoculated on 19 June 2003 by removing a soil core (1.9 × 10.3 cm) from the center of each plot, adding 25 cm3 of M. poae-infested rye grains, and then capping the hole with sand. Growth chamber and field inoculations were arranged in a randomized complete block with four replications. Eight weeks after inoculation in the growth chamber, isolates TAP35, TAP41, and SCR4 caused significant foliar chlorosis and dieback at 12-h day/night cycles of 30/25°C and 35/25°C, but only TAP41 induced symptoms at 40/25°C. Isolate TAP42 did not induce symptoms at any temperature regimen. Orange patches (10 to 15 cm in diameter) were observed in field plots inoculated with TAP41 on 27 August 2003. No other isolates induced aboveground symptoms. Roots and crowns of plants exhibiting foliar symptoms in the greenhouse and field were necrotic and colonized with ectotrophic hyphae, and M. poae was consistently isolated from this tissue. Although M. poae has been associated with CRB in Florida (1), to our knowledge, this is the first report of summer patch of CRB within the normal zone of adaptation for this turfgrass species. Observation of this disease highlights the need for accurate methods for diagnosis of diseases caused by ectotrophic root-infecting fungi.

References: (1) M. L. Elliott. Plant Dis. 77:429, 1993. (2) M. E. Juhnke et al. Plant Dis. 68:233, 1984. (3) P. J. Landschoot and N. Jackson. Mycol. Res. 93:59, 1989. (4) E. S. Lutrell. Phytopathology 48:281, 1958.