Leaf Blight of Alnus rhombifolia and A. cordata Caused by Xanthomonas campestris. A. L. Bishop, California Department of Food and Agriculture, P.O. Box 942871, Sacramento 94271-0001. L. Basarich, California Department of Food and Agriculture, P.O. Box 942871, Sacramento 94271-0001. Plant Dis. 73:610. Accepted for publication 27 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0610C.
Yellow pigmented bacteria were consistently isolated from necrotic lesions and adjacent symptomless tissue on leaves of white alder (Alnus rhombifolia Nutt.) and ltalian alder (A. cordata (Loisel.) Duby) grown under sprinkler irrigation in a local nursery. Leaf lesions were irregular, dry, tan, and partially delimited by the main veins. Dark lines, 1-3 mm wide and roughly parallel to the margins of the lesions, created irregular concentric zones. Necrotic areas eventually disintegrated, causing tattering of severely affected leaves. The pathogen was also recovered from surface-sterilized, peeled twigs, indicating that infection was systemic. Inoculation of seedlings of A. rhombifolia and A. cordata by atomization of bacterial suspensions reproduced symptoms in 3-4 wk; the pathogen was recovered from lesions and adjacent symptomless tissue of inoculated plants. The pathogen was identified as Xanthomonas campestris (Pammel) Dowson on the basis of its gram-negative reaction, production of xanthomonadins, mucoid growth on glucose-containing media, requirement for oxygen, acidification of carbohydrates, lack of urease, and ability to hydrolyze starch, casein, Tween 80, and esculin. This is the first report of X. campestris causing a disease of Alnus.