Butternut seedlings from North Carolina (S. Schlarbaum, University of Tennessee) were planted during the spring of 2005 in an open space at the edge of the Mattatuck State Forest in Plymouth, CT. There were mature butternuts with visible cankers that were at the forest edge and out of reach. In May 2006, some seedlings had died and many small, dark lesions were found on the twigs and stems of living seedlings. Stems with lesions were surface sterilized with 10% bleach, rinsed with sterile water, the epidermis peeled away, and slices of the wood were placed on the surface of 2% water agar plates. From these, we consistently isolated a Phomopsis sp. that grew well on potato dextrose agar (PDA) at 28°C and produced alpha and beta spores (average 8 × 2 μm and 25 × 1 μm, respectively). A mixture of six such isolates on autoclaved pieces of butternut stem supported by water agar produced perithecia after 6 months with ascospores that matched the description of Diaporthe eres (two-celled, slightly constricted at the septum, and averaged 12 × 3 μm). Two of our isolates of Diaporthe eres, both of which were weakly pathogenic and recovered from the lesions, were inoculated into cut, dormant stems of butternut ‘Buckley’ in the laboratory, This ascomycete was reported to be a pathogen of Juglans ailantifolia and J. regia var. orientes in Japan (1) but has not been reported on J. cinerea. There is a rather vague report of Diaporthe spiculosa on other species of Juglans and Phomopsis juglandina on twigs (with a question mark) of J. regia (with a question mark) in California (2). These were not reported by T. Kobayashi.
References: (1) T. Kobayashi. Bull. Gov. For. Exp. Stn. No. 226, 1970. (2) U.S. Dep. Agric. Index of Plant Diseases in the United States. Agric. Handb. No. 165, 1960.
