Quercus canariensis, a New Host of Trabutia quercina.

Abstract

Quercus canariensis Willd. is an oak species endemic to northwestern Africa and the Iberian Peninsula. This species is particularly abundant in the southwestern Andalucía Region of southern Spain. During a disease survey in this area from 1997 to 1998, we observed Q. canariensis trees affected by a tar spot disease. Tar spot lesions were clearly differentiated by a black, crustose, and shiny stromata (10 to 20 mm in diameter) on the upper surface of leaves mainly arranged along leaf veins but also scattered randomly over the leaf surface. On most leaves there was little necrosis, and on most trees the damage was not serious, although some trees located in the most humid areas were severely affected with leaf chlorosis and heavy defoliation. Other Quercus species in the area, such as Q. ilex and Q. suber, did not show signs of tar spot. One fungus species was consistently associated with tar spots. The fungus formed ascomata, 250 to 400 µm in diameter, embedded in the stromata. Asci were clavate or saccate, 45 to 55 × 17 to 22 µm, eight spored, and short stalked. The ascus apex was acute to obtuse. Ascospores were arranged irregularly, 20 to 25 (-30) × 5 to 8.5 µm, fusiform to ellipsoidal fusiform, often curved and flattened on one side, thin walled, hyaline, aseptate, and smooth without a gelatinous sheath or appendage. Based on these characteristics, the fungus was identified as Trabutia quercina (Rudolphi ex Fr.) Sacc. & Roum., a pathogen causing tar spot in several Quercus species in the Northern Hemisphere (1). Samples were deposited in the Plant Pathology Mycotheca at the University of Córdoba, Spain (MIC-888 to MIC-897). To our knowledge, this is the first report of T. quercina on Q. canariensis and the first report of this pathogen in Spain. Reference: (1) P. F. Cannon. Mycopathologia 135:69, 1996.