Testing virulence of Cryphonectria parasitica strains
A rapid and reproducible method for the differentiation of virulent and hypovirulent Cryphonectria parasitica (EPPO A2 pest) strains has been developed in Massachusetts, USA. The method is simply based on the different growth rate of the fungal strains. Bark and wood-tissue samples of chestnut were inoculated with virulent and hypovirulent strains of the pest and then incubated for 4 days at 25ø C. The pest was then assessed by measuring the area of the tissues which had brown, necrotic cells. Hypovirulent strains damaged an area of 2,16 cmý or even less while virulent strains damaged an area of over 3,6 cmý. To confirm the tests, chestnut trees were inoculated with the strains of C. parasitica and the results were compared with the results of the laboratory test. It showed that the laboratory test was a very reliable method to assess the virulence of C. parasitica strains. The authors believe that the new method should be very useful as an initial screening method for rapid selection of C. parasitica strains with a good hypovirulent potential.
Sources
Lee, J.K.; Tattar, T.A.; Berman, B.M.; Mount, M.S. (1992) A rapid method for testing the virulence of Cryphonectria parasitica using excised bark and wood of American chestnut.
Phytopathology 82, 1454-1456.