Archivio Journal of Plant Pathology

Abstract:

Red oak or Tuchi (Quercus crassipes) is an ornamental endemic species of Mexico. On November 9, 2016, powdery mildew was observed on leaves of Tuchi in Santa Fe, Mexico City. The symptoms and signs included deformed leaves, irregular necrotic lesions on both sides of the leaf, premature leaf drop, chasmothecia and mycelium. A reference specimen (CMPH-ECO23S) was deposited in the Herbarium of the Colegio de Postgraduados. The fungus produced light brown to dark reddish chasmothecia immersed in the mycelium. Chasmothecia were grouped or dispersed, 99-111 µm in diameter, composed of polygonal peridial cells of 12-18 µm; with simple, sinuous, poorly developed, short, or almost absent mycelial appendages (4-4.5 µm wide) that were interlaced with the surrounding mycelium. The single ascus was hyaline, ellipsoid or ovoid to globose, sessile, 80-91 x 55-68 µm to 134 x 85 µm. The ascospores were hyaline, ellipsoid to ovoid, 25-32 x 18-22 µm. Conidiophores and conidia were not observed. Amplification of ITS was carried out using primers ITS4 and ITS5. The PCR product (459 bp) was sequenced and deposited in GenBank (accession No. MF170000). The obtained sequence showed 100% similarity to AF011289 from Q. agrifolia. No extype sequence of C. lanestris is in GenBank, but the type and this sequence are from Q. agrifolia in California, USA. Based on morphological and molecular characteristics, the fungus observed on Quercus crassipes was identified as Cystotheca lanestris (Braun and Cook, 2012). To our knowledge, this is the first report of this fungus causing powdery mildew of red oak in Mexico.