First Report of Powdery Mildew Caused by Leveillula taurica on Capparis spinosa subsp. himalayensis from China

Abstract

Capparis spinosa subsp. himalayensis (Capparaceae) as a wild plant grows widely in Xinjiang and Tibet of China, as well as northern India and Pakistan (Fici 2015; Zhang and Tucker 2008). Its root, barks, leaves, and fruits are used for the treatment of rheumatism in traditional medicine. Since 2010, C. spinosa subsp. himalayensis has been affected by a powdery mildew with nearly 80% disease incidence in the northwest of Taklimakan desert, Xinjiang, China. Symptoms of powdery mildew first appear as circular to irregular white colonies, which subsequently develop into an abundant growth on the upper and lower surface of the leaves. As the disease progresses, the infection spreads to whole leaves, resulting in leaf death and decreased medicinal value. Two representative specimens were deposited in the Mycological Herbarium of Tarim University (HMUT0911551 and HMUT0911552). Mycelium was abundantly hypophyllous, sometimes amphigenous, forming thin white patches or covering entire leaves. Conidiophores emerged through leaf stomata, singly or branched, and formed dimorphic conidia. Primary conidia were lanceolate with distinct apical points measuring 44 to 63 × 12 to 22 μm. Secondary conidia were ellipsoid to cylindrical measuring 41 to 59 × 12 to 20 μm. Both conidia were hyaline with angular/rectangular wrinkling of the outer walls. The chasmothecia were nearly gregarious and globe-shaped, 98 to 249 μm in diameter, often immersed in dense mycelial tomentum with numerous asci. Numerous and well-developed appendages on the lower half of the chasmothecia were irregularly branched. Asci were stalked, long or wide ellipsoidal in shape, and 84 to 136 × 25.4 to 56.8 μm. The asci usually contained two ellipsoidal, colorless ascospores measuring 22.8 to 46.7 × 15.4 to 28.7 μm. The specific measurements and morphological features were consistent with those of Leveillula taurica (Lev.) Arnaud (Braun and Cook 2012). To confirm the identification, the internal transcribed spacer (ITS) and 28S rDNA of isolates HMUT0911551 and HMUT0911552 were amplified and sequenced as described by Song et al. (2016). NCBI BLAST search indicated that the ITS sequences (GenBank accession nos. MG600237 and MG600238) were 99.8% (identity: 610/611) similar to L. taurica on C. spinosa and Rosa sp. from Iran (accession nos. AB045002 and AB667881) (Khodaparast et al. 2001). It also indicated that the 28S sequences (GenBank accession nos. MG600239 and MG600240) were 100% similar to L. taurica on Glancium oxylobum and Alcea sp. from Iran (accession nos. AB080474 and AB080467) (Takamatsu et al. 2008). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of healthy potted plants. Six inoculated plants were kept under a plastic humid chamber, and three noninoculated plants served as the control. The plants were placed under greenhouse conditions at 25 to 30°C for 7 days. Typical symptoms of powdery mildew developed on the inoculated plants, with identical morphology to the original observation on diseased leaves. No symptoms were seen on the control plants. To our knowledge, this is the first report of powdery mildew caused by L. taurica on C. spinosa subsp. himalayensis. This study extends the host range of L. taurica.