Section 25
Chapter 24,222

Bark canker, a bacterial disease of the Persian walnut tree

Wilson, E.E.; Starr, M.P.; Berger, J.A.

Phytopath 47(11): 669-673


Accession: 024221411

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An apparently undescribed disease of Persian (English) walnut was found in the Sacramento Valley of California in 1955. The disease is characterized by extensive, shallow, irregularly shaped cankers in the bark of the trunk and scaffold branches of mature trees. Cankers expand throughout the summer but are inactive in winter. A bacterium that is present in large numbers in the affected bark proved to be the causal organism. It is a gram-negative, peritrichous, nonpectinolytic bacillus related to the fireblight organism, Erwinia amylovora. By direct comparison, it was possible to distinguish the 2 organisms with sufficient certainty to warrant the designation of the walnut pathogen as Erwinia nigrifluens.

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