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Genetic variation in the rose pathogen Marssonina rosae estimated by RAPD
63-67.Views:183Blackspot, caused by the fungus Marssonina rosae (Diplocarpon msae), is one of the most devastating and widespread diseases in garden roses, and it has as yet not been fully characterized in molecular terms. In this initial study we used RAPD analysis to investigate the genetic diversity among and within a few geographically diverse groups of single-spore isolates of M. rosae. DNA was extracted from in vitrogrown mycelia of 1 I single spore isolates grown on PDA medium. High levels of polymorphism were detected among the isolates. They clustered into three distinct groups: Group !consisted of isolates from eastern North America plus a European isolate (Germany), Group 2 included isolates from southern Sweden, and Group 3 included the isolates from Manitoba, Canada. The greater similarity of the environmental conditions in eastern North America and Europe as compared to the Canadian prairies suggest that. climate and weather could be key factors in influencing the potential race structure of M. rosae. However, variations among closely situated sites, e.g. southern Sweden, also occurred.
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Impact of foliar fungi on dogroses
23-30.Views:194Wild roses of the section Caninae, commonly known as dogroses, have been described as more disease tolerant than ornamental roses and could therefore become valuable for breeding improved rose cultivars. Two fields with dogroses, one with plants obtained by open pollination in wild populations, and one with plants obtained from intra- and interspecific crosses, were evaluated for blackspot, powdery mildew, rust and leafspots in the autumn of 2005. Symptoms of the different fungi on different dogrose species were carefully evaluated in a microscope and documented by photography. Interestingly, almost no symptoms of powdery mildew were found in either field, although the fungus infected wild roses of a different section in a field closeby. Surprisingly few symptoms were found also of blackspot, and they differed considerably from those found on ornamental cultivars, indicating a lower susceptibility in dogroses. The most important fungal disease in 2005 was rust, followed by leafspot symptoms. The latter were apparently caused by Sphaceloma rosarum and Septoria rosae which can be properly discriminated only in a microscope. The investigated dogrose species and their progeny groups varied significantly in disease susceptibility and in the appearance of encountered symptoms but there was no evidence of major resistance genes, except possibly in Rosa rubiginosa which did not show any symptoms of Septoria. In 2006, a subset of the plant material in Field 1 was evaluated to check for consistency between the years. Leafspots had overtaken rust as the most important disease but results were otherwise very similar to those of 2005.