First molecular detection of Ramularia leaf spot (Ramularia collo-cygni) in seeds and leaves of barley in Argentina
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The fungus Ramularia collo-cygni B. Sutton & J. M. Waller (Rcc) was identified as the causal agent of this emerging disease on barley (Hordeum vulgare L.) based on symptoms and signs on leaves and attributes of the fungus. The common name given to the disease was “necrotic sprinkling.” This disease was found for the first time on barley in fields of Buenos Aires Province, Argentina, in 2001, with severities ranging from 60 to 100% (2). During the spring of 2012, the disease spread throughout most barley growing areas of the Pampean region, affecting almost all varieties of barley in the Buenos Aires, Entre Ríos, and Santa Fe provinces. The disease showed typical symptoms of small, brown spots on leaves, sheaths, and awns, and caused rapid loss of green leaf area and significant economic damage. The diagnosis of this disease is difficult by conventional techniques and has caused some confusion. In order to obtain appropriate information about the incidence of this pathogen in the most important barley growing region of Argentina, as well as to confirm its presence on seed, 39 seed samples containing 200 seeds each and eight leaf samples were analyzed using a real-time PCR diagnostic test (4). Thirty-five of the 37 seed samples had Rcc DNA levels above the minimum detection level (0.13 pg DNA). Ramularia has been described as a seedborne fungus previously (1) and seed infection could hasten the spread of the fungus to new geographically distinct areas. Moreover, leaf samples were microscopically assessed for conidophore presence and then ground for DNA extraction. Rcc DNA was detected by PCR in all eight leaf samples. To our knowledge, this is the first report about molecular detection of R. collo-cygni in barley seed of harvested samples from Argentina. Seeds infected/infested may also lead to new strains of the fungus arriving in barley fields and provide a source of inoculum for future epidemics (3).
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