Foreign Disease-Weed Science Research Unit, USDA/ARS, 1301 Ditto Avenue, Fort Detrick, MD 21702
Systematic Botany and Mycology Laboratory, USDA/ARS, Room 304, Building 011A, 10300 Baltimore Avenue, Beltsville, MD 20705-2350
European Biological Control Laboratory, Thessaloniki, Greece
Crupina vulgaris Cass. (common crupina, family Asteraceae), an introduced invasive weed in the northwestern United States, is a target of biological control efforts. During the spring of 2002, ≈30 wilting C. vulgaris plants were found along a road from Volos to Portaria, Greece (39°22′58″N, 22°59′27″E, elevation 446 m). Wilting plants had irregular, purple, necrotic lesions extending along the main stems and petioles. In the laboratory, diseased leaves were surface disinfested and placed on moist filter paper in petri dishes. Acervuli with setae typical of a Colletotrichum sp. were observed after 2 to 5 days. A fungal isolate, DB 02-030, was isolated from these diseased leaves. Stems and leaves of 12- and 16-week-old plants (12 plants of each age) were spray inoculated with an aqueous suspension of 2 × 106 conidia per ml from 14-day-old cultures of DB 02-030 grown on acidified potato dextrose agar (APDA). Inoculated plants were placed in a dew chamber at 18 to 21°C with continuous dew and 8 h of light per day for 48 h. Plants were moved to a greenhouse bench with 8 h of light per day and watered twice daily. Symptoms developed after 7 days on 16-week-old plants (33% symptomatic) and 14 days on 12-week-old plants (17% symptomatic). No symptoms developed on control plants. By 61 days after inoculation, 67% of plants inoculated at 16 weeks of age were dead and 50% of plants inoculated at 12 weeks of age were wilted. Koch's postulates were repeated with isolates from two other plants. Isolate DB 02-030 was reisolated three times from 10 of 10 symptomatic leaves, 4 of 4 stems with necrotic lesions, and 4 of 4 stems with leaves from wilted inoculated plants. Conidia germination on water agar was 95% at 18 to 21°C with light compared with 19% in darkness or at 23 to 26°C. C. vulgaris is an annual plant that emerges during early spring and reproduces only by seeds. As a cool-temperature aggressive pathogen, isolate DB 02-030 has the potential as a biological control agent to reduce seed production and stands of C. vulgaris. This isolate fits the morphology of Colletotrichum gloeosporioides according to Sutton (2). On APDA, conidia were formed after 4 days. Conidia were hyaline, straight, cylindrical, nonseptate, and 18 to 27 × 3 to 6 μm. Setae produced in acervuli were abundant, straight, narrow, and 75 to 210 μm long × 3 μm at the base. Appressoria in vitro were subglobose to clavate and 8 to 12 μm in diameter. Nucleotide sequences were obtained for the internal transcribed spacer (GenBank Accession No. AY539806) and 28S (GenBank Accession No. AY539807) rDNA genes of this isolate. Parsimony analyses (unpublished), with sequences from GenBank and 25 isolates from established culture collections, indicate the isolate on C. vulgaris belongs to a clade of taxonomically problematic Colletotrichum spp. that are only distantly related to other isolates of C. gloeosporioides. A culture of DB 02-030 has been deposited at the Centraalbureau voor Schimmelcultures as CBS 114801. A dried culture voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 843682). To our knowledge, no species of Colletotrichum has been reported previously on any Crupina spp. (1).
References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, On-line publication. ARS, USDA, 2004. (2) B. C. Sutton. The Coelomycetes. CMI, Kew, Surrey, England, 1980.