First Report of Downy Spot of Walnuts Caused by Microstroma jug-landis in Spain. J. Garcia-Jimenez, Departamento de Produccion Vegetal, Universidad Politecnica de Valencia, Camino de Vera 14, 46020 Valencia, Spain. J. Armengol, and G. Martinez-Ferrer, Patologia Vegetal, Departamento de Produccion Vegetal, Universidad Politecnica de Valencia, Camino de Vera 14, 46020 Valencia, Spain. Plant Dis. 79:860 . Accepted for publication 12 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0860B.
During the summer of 1991, walnuts (Juglans regia L.) from orchards in Valencia, in eastern Spain, exhibited symptoms of a foliar spot disease. Whitish polygonal efflorescences were observed on the lower surface of affected leaves and discolored light green blotches on the upper surfaces. When leaf spots enlarged, affected tissues collapsed and became necrotic. Some defoliation occurred, with most of the leaves remaining on the trees. Examination of leaf infections using light microscopy showed that efflorescences were basidial structures bearing oval basidiospores (3 to 7 x 2 to 3 urn). Colonies on potato-dextrose agar were somewhat mucoid, white or cream-colored, and yeasllike. Microscopically, colonies consisted of ellipsoidal to ovoid or clavate cells that reproduced by unipolar budding (1). Bud cells were similar in size to basidiospores. The fungus was identified as Microstroma juglandis (Berenger) Sacc. (Hymenomycetes, order Exo-basidiales). Although disease incidence was not very high, walnuts in several Spanish areas have been checked during the last 3 years, and the fungus was also detected in 1993 to 1994 affecting noncultivated walnut trees in a rainy area of Leon, northwestern Spain. This fungus has been previously reported in the United States, Bulgaria, India, and New Zealand (2). This is the first report of occurrence of downy spot of walnut in Spain.References: (1) J. A. von Arx et al. Mycologia 74:285, 1982. (2) H. J. Boesewinkel. N. Z.J.Agric. 135:21, 1977.