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Butternut (Juglans cinerea) is being killed throughout its native range by the fungus Sirococcus clavigignenti-juglandacearum (Scj). In recent years, many disease-free trees have been determined to be complex hybrids with an admixture of Japanese walnut (J. ailantifolia). We challenged 5-year-old trees from two progeny tests with Scj in 2008. The first test (northern Indiana), planted in 2003, had 37 diverse families (n=319). Thirty-two of these seedling families were derived from a grafted orchard. Five additional families were collected from hybrid trees. The second test (southern Indiana), planted in 2004, had 12 pure butternut half-sib families collected from a woodlot with: 4 resistant, 4 moderately resistant, 4 susceptible, and 1 resistant hybrid families (n=213). Resistance ratings were based on the disease status of the mother trees when the seed was harvested in the fall of 2002. Eleven black walnut (J. nigra) trees were also included. In early fall of 2008, trees were inoculated with two strains of Scj obtained from branch cankers on trees in two locations in Indiana. The trees were scored 8 months after inoculation for canker incidence and severity. Some trees in the first test were naturally infected by Scj and resulting canker incidence and severity were recorded. Butternut hybrid families were more resistant to natural infection than the pure butternut families. Eight months after inoculation, canker incidence and severity varied significantly among butternut hybrid families and Scj strain but not among pure butternut families. |
