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Production and Dispersal of Ascospores of Eutypa armeniacae in California. D. E. Ramos, Department of Plant Pathology, University of California, Davis, CA 95616; W. J. Moller(2), and Harley English(3). (2)(3)Department of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 65:1364-1371. Accepted for publication 24 June 1975. DOI: 10.1094/Phyto-65-1364.

Mature perithecial stromata of Eutypa armeniacae develop readily on dead, -infected apricot wood in the high (> 508 mm) rainfall area around San Francisco Bay. Stromata are sparsely distributed in other apricot districts where the mean annual rainfall exceeds 330 mm, but are not present in the more arid interior valley districts. Grape and Ceanothus, two additional hosts of E. armeniacae, do not contribute significantly to the spore inoculum in California. A two-year study of the seasonal abundance of airborne ascospores showed a period of low ascospore frequency in late fall and early winter, but the only safe period for pruning apricot trees is during the dry summer months. Evidence is presented for long-distance dispersal of airborne ascospores from areas of high (> 508 mm) rainfall to the interior valley apricot-producing districts. Inoculum levels of E. armeniacae were compared for their ability to infect fresh pruning wounds in apricot trees. Infection resulting from 1, 10, or 100 ascospores per wound was not significantly different when wounds were inoculated during tree dormancy, whereas infection by one ascospore during the growing season was significantly lower than that caused by 10 or 100 ascospores.

Additional keywords: epidemiology, Cytosporina dieback, apricot.