Poster Session: Detection and Diagnosis - Fungi and Oomycetes
Distribution and host range of Colletotrichum acutatum on Salicaceae in San Francisco’s North Bay area.
S. SWAIN (1), S. T. Koike (2)
(1) University of California, Novato, CA, U.S.A.; (2) University of California Cooperative Extension, Salinas, CA, U.S.A.
Weeping willow trees (Salix babylonica L.) are widely planted in riparian landscapes in Marin County, CA, USA. Following prolonged spring rains and cool summer weather in 2010, mature weeping willows showed symptoms of a disease subsequently identified as twig canker caused by Colletotrichum acutatum. Small branches developed dark brown to black, sunken cankers, 3 to 20 cm in length, similar in appearance to those produced by other willow canker pathogens, such as Colletotrichum gloeosporioides (anamorph: Glomerella miyabeana) (black canker) and Venturia salciperda (willow scab). Badly infected willows declined as a result of repeated defoliation and twig loss. Disease severity on afflicted trees was markedly lower in 2011 and 2012, presumably due to warmer, drier weather. Since willow cuttings are frequently used for habitat restoration projects, understanding the extent to which the disease may have migrated to native willows was key to assessing the need to prevent its transmission into uninfested areas. To do this, we needed to determine its distribution and whether other pathogens or hosts were involved. Symptomatic Populus nigra (Lombardy poplar) grow within a few miles of infected willows, and tested as highly susceptible to infection by willow isolates of C. acutatum. Brief surveys have been conducted to find infected poplar, and differentiate symptoms from those produced by pathogens such as Cryptodiaporthe salicella.
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