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Etiology

Etiological Role of the Xylem-Limited Bacterium Causing Pierce’s Disease in Almond Leaf Scorch. M. J. Davis, Former graduate research assistant, Departments of Plant Pathology and Entomological Sciences, University of California, Berkeley 94720, Present address: Department of Plant Pathology, Cook College, Rutgers University, New Brunswick, NJ 08903; S. V. Thomson(2), and A. H. Purcell(3). (2)(3)Assistant professors, respectively, Departments of Plant Pathology and Entomological Sciences, University of California, Berkeley 94720, (2)Present address: Department of Biology, Utah State University, Logan 84322. Phytopathology 70:472-475. Accepted for publication 7 December 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-472.

A xylem-limited bacterium resembling the bacterium that causes Pierce’s disease (PD) of grapevines was isolated from 17 of 20 almond trees (Prunus amygdalus) with almond leaf scorch (ALS) symptoms but not from 16 symptomless trees in two orchards in California. The bacterium was isolated from symptomatic trees in both orchards throughout one summer on 22 of 23 (95.7%) and 34 of 60 (56.7%) attempts. PD or ALS symptoms developed in their respective hosts when inoculated with bacterial strains from either host. Injections with a syringe and hypodermic needle were an efficient means of inoculating both hosts. ALS symptoms were more extensive and the bacteria were reisolated more frequently when trees in varietal blocks were inoculated with bacteria by injection than by leafhopper (Draeculacephala minerva) transmission. Few first-year infections survived the winter.