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Etiology

Branch Dieback of Southern California Chaparral Vegetation Caused by Botryosphaeria dothidea. F. E. Brooks, Graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521; D. M. Ferrin, assistant professor, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 84:78-83. Accepted for publication 13 September 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-78.

Branch dieback in the southern California chaparral was reported in 1985, the first year of a 5-yr drought. The pathogen was identified as a Dothiorella-like anamorph of Botryosphaeria dothidea. B. dothidea has been isolated from active lesions on over 50 species and cultivars of California native plants. Field inoculations during September 1990 with isolates of B. dothidea from four of these hosts resulted in rapid disease development. Lesions measured 60–80 mm long after 1 wk, and most of the branches were killed after 6 wk. Maximum in vitro vegetative growth occurred at 25–30 C for three isolates from southern California. Conidial germination was greatest at 30 C and declined at temperatures below 30 C. Germination at 30 C for two isolates was 98% at 12 h and 85–100% after 24 h at temperatures from 10 to 30 C. Germination and growth of the southern California isolates of B. dothidea tested at high temperatures were similar to those of isolates from the southeastern United States. Germination at low temperatures, however, was noticeably greater for the southern California isolates tested than the germination reported for isolates from the southeastern United States.