Mile-a-minute (Persicaria perfoliata (L.) H. Gross; family: Polygonaceae) is an exotic annual barbed vine that has invaded the northeastern USA and Oregon (2). In July of 2010, in a search for potential biological control pathogens (3), diseased P. perfoliata plants were found along the Firtina River near Ardesen, Turkey. Symptoms were irregular dark necrotic lesions along leaf margins and smaller irregular reddish lesions on the lamellae of leaves. Symptomatic leaves were sent to the quarantine facility of FDWSRU, USDA, ARS in Ft. Detrick, MD, for pathogen isolation and testing. Symptomatic leaves were excised, surface disinfested in 0.615% NaOCl, and then incubated for 2 to 3 days in sterile moist chambers at 20 to 25°C. Numerous waxy sub-epidermal acervuli with 84-μm-long (mean) black setae were observed in all of the lesions after 2 to 3 days of incubation. Conidiophores within acervuli were simple, short, and erect. Conidia were one-celled, hyaline, guttulate, subcylindrical, straight, 12.3 to 18.9 × 3.0 to 4.6 μm (mean 14.3 × 3.7 μm). Pure cultures were obtained by transferring conidia onto 20% V-8 juice agar. Appressoria, formed 24 h after placing conidia on dialysis membrane over V-8 juice agar, were smooth, clavate, aseptate, regular in outline, and 6.4 to 10.0 × 5.1 to 7.2 μm (mean 7.5 × 6.6 μm). These characters conformed to the description of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. (1). A voucher specimen was deposited in the U.S. National Fungus Collections (BPI 882461). Nucleotide sequences for the internal transcribed spacers (ITS 1 and 2), directly sequenced from ITS 1 and ITS 4 standard primers (4), were deposited in GenBank (JN887693). A comparison of these sequences with ITS 1 and 2 sequences of the C. gloeosporioides epitype IMI 356878 (GenBank EU 371022) (1) using BLAST found 479 of 482 identities with no gaps. Conidia from 14-day-old cultures, in an aqueous suspension of 1.0 × 106 conidia ml–1, were spray-inoculated onto healthy stems and leaves of twenty 30-day-old P. perfoliata plants. Another 10 plants were not inoculated. All plants were placed in a dew chamber at 25°C for 16 h with no lighting. They were then placed in a 20 to 25°C greenhouse with a 14-h photoperiod. Light was generated using 400W sodium vapor lights. Lesions developed on leaves and stems of all inoculated plants after 7 days, and symptoms were the same as observed in the field. Each plant was rated weekly for disease severity on a 0 to 10 rating scale where 0 = no disease symptoms and 10 = 100% symptomatic tissue. After 28 days, the average disease rating of inoculated plants was 3.95 ± 0.94. No disease developed on noninoculated plants. C. gloeosporioides was reisolated from all inoculated plants. Host range tests will determine the potential of this isolate as a biological control agent for P. perfoliata. To our knowledge, this is the first report of anthracnose caused by C. gloeosporioides on P. perfoliata.
References: (1) P. F. Cannon et al. Mycotaxon 104:189, 2008. (2) J. T. Kartesz and C. A. Meacham. Synthesis of the North American Flora, Version 1.0., North Carolina Botanical Garden, Chapel Hill, N.C. 1999. (3) D. L. Price et al. Environ. Entomol. 32:229, 2003. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, Inc., San Diego, CA, 1990.