A RAPID METHOD FOR TESTING THE VIRULENCE OF CRYPHONECTRIA-PARASITICA USING EXCISED BARK AND WOOD OF AMERICAN CHESTNUT

A rapid and reproducible method for testing the virulence of Cryphonectria parasitica using American chestnut (Castanea dentata) was developed. Bark- and wood-tissue samples excised from American chestnut tree stems were inoculated with virulent and hypovirulent C. parasitica strains. Samples were incubated at 25 C for 4 days, and virulence was assessed as the area of bark and wood tissue having brown, necrotic cells. Hypovirulent strains damaged an area 2.16 cm2 or less of each tissue sample, while virulent strains consistently damaged a greater area (3.62-3.67 cm2). Living trees and excised stems were inoculated with the same fungal strains; the test results were compared to those from bark/wood tests. The virulence-assessment data from trees and cut stems correlated well with bark/wood data. However, the bark/wood-tissue test was superior in terms of the incubation time required, convenience, and data reproducibility. This procedure should be extremely useful as an initial screening of C. parasitica strains for hypovirulence.