Archivio Journal of Plant Pathology

Abstract:

During February-April 2013, symptoms of powdery mildew were observed in trees of black cherry (Prunus serotina subsp. capuli) in Tlaxcala (Mexico). Symptoms appeared as irregular necrotic lesions on both sides of the leaves. Fungal growth was present only on the abaxial surface. In severe infections, distortion of the leaves was observed. The preliminary identification of the fungus was performed by examination of morphological characters. Hyphae were septate, hyaline, thin-walled, and smooth. Conidiophores were 109-158 μm long, straight, erect, arising non centrally from superficial hyphae. Foot-cells were cylindrical, slender, 55-73x 8-10 μm, followed by 1 or 2 shorter cells. Conidia were ellipsoidal-ovoid to doliiform, 24-33x 13-19 μm. Germ tubes were more or less terminal to lateral, simple, short to moderately long. Chasmothecia were not found. The morphological characters were consistent with those of the anamorphic state of Podosphaera clandestina, but also with the imperfect state of P. pannosa (Braun and Cook, 2012). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4 and ITS5 (White et al., 1990), and sequenced directly. The resulting sequence of 565 bp was deposited in GenBank under the accession No. KJ158161. Comparison with sequences from GenBank revealed that our sequence was 100% identical with the sequence of P. clandestina on Prunus laurocerasus (accession No. AF011317). Based on the morphology and ITS rDNA sequence analysis, the fungus was identified as P. clandestina. To our knowledge, this is the first report of P. clandestina causing powdery mildew on black cherry in Mexico.