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Etiology

Plum Leaf Scald: Isolation, Culture, and Pathogenicity of the Causal Agent. B. C. Raju, Department of Plant Pathology, University of California, Davis 95616, Present address: c/o Yoder Bros., P.O. Box 68, Alva, FL 33920; J. M. Wells(2), G. Nyland(3), R. H. Brlansky(4), and S. K. Lowe(5). (2)Southeastern Fruit and Tree Nut Research Laboratory, Science and Education Administration, U.S. Department of Agriculture, Byron, GA 31008; (3)(5)Department of Plant Pathology, University of California, Davis 95616; (4)University of Florida, Institute of Food and Agricultural Science (IFAS), Lake Alfred 33850. Phytopathology 72:1460-1466. Accepted for publication 14 April 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982.. DOI: 10.1094/Phyto-72-1460.

A Gram-negative bacterium with rippled cell walls was consistently isolated on a cell-free medium from petiole, stem, and root tissues of plum showing leaf scald symptoms. Similar bacteria were also isolated from peach affected with phony disease, but not from healthy plants. Colonies developed in 8–16 days on BC-YE or BC-ZE medium and reached 0.1 to 0.9 mm in diameter after 3 wk. Bacterial cells measured 0.35 μm in diameter and 2–5 μm in length. One-year-old cultivar Myro plum seedlings inoculated with pure cultures of bacterial inoculum from plum or peach showed typical leaf scald symptoms in 5–6 mo. No symptoms were seen in plum controls. Bacteria isolated from all inoculated plums showing symptoms were morphologically, ultrastructurally, and serologically identical to original isolates from naturally diseased plum. Almond trees inoculated with plum bacteria showed no symptoms. Antiserum to the plum leaf scald bacterium reacted positively with extracts from diseased plum in ELISA and with tissue sections in immunofluorescence. No serological or pathological differences were observed among isolates of plum leaf scald bacteria from Georgia, Florida, and Argentina and the bacterium associated with phony peach disease. The plum leaf scald bacterium in pure culture or in diseased plants could be serologically distinguished from the Pierce’s disease bacterium by ELISA and by its lack of pathogenicity on almond.