Pathogenicity and Sporulation of Normal and Diseased Strains of Endothia parasitica in American Chestnut

Normal strains ( all lacking double-stranded RNA) and diseased strains ( all containing double-stranded RNA) of Endothia parasitica were screened for pathogenicity and asexual sporulation in excised dormant American chestnut stems in the laboratory and for pathogenicity, asexual, and sexual sporulation in intact trees in the field. Representative strains were included from French, French-derived American, Italian, and native American collections. In excised stems, normal strains from all collections produced rapidly expanding cankers with abundant pycnidia and spore tendrils. Diseased strains from the French collection and American diseased strains derived from them were either nonpathogenic or produced small cankers that did not enlarge or sporulate. Diseased strains from the Italian and native American collections exhibited wider ranges of pathogenicity and capacity to sporulate. Cankers produced by diseased strains in excised stems and intact trees could be distinguished from those produced by normal strains by their smaller size, fewer pycnidia and spore tendrils, or both. Only 2 of 17 pathogenic diseased strains produced perithecia and ascospores under field conditions during the six months after inoculation, and these were produced in very low numbers compared with normal strains.

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Author(s): John E. Elliston

Publication: American Chestnut Proceedings - 1978