First Report of Podosphaera xanthii Causing Powdery Mildew on Mungbean (Vigna radiata) in Taiwan

Mungbean (Vigna radiata L.) is routinely grown in the experimental fields at headquarters of World Vegetable Center (23°6'30.88N, 120°17'51.31E) for breeding, research and germplasm multiplication. In a spring 2016 mungbean trial, about 50% plants were affected with powdery mildew. The white, powdery-like patches first appeared on upper leaf surfaces, soon developed to grey both sides leaves. Purple brown discoloration underside infected leaf. Microscopy examination revealed that causal organism was not Erysiphe polygoni, which had previously been documented as mildew pathogen Taiwan (Hartman et al. 1993). fungus produced typical structures Euoidium, anamorph genus Podosphaera. mycelium consisted septate, flexuous hyphae indistinct appressoria. erect conidiophores arising from superficial varied straight or slightly curved curled. Three ten conidia borne long chains crenate edges. Foot-cells straight, cylindrical measured 30 52 µm long. Conidia hyaline, ellipsoid-ovoid barrel-shaped, fibrosin bodies, 27 33 (mean = 30.4) × 15 20 16.6) µm. Germ tubes clavate occasionally forked, lateral sites conidia. No chasmothecia found samples. morphological characteristics consistent P. xanthii (Castagne) U. Braun & Shishkoff (Braun Cook 2012). To confirm identity, internal transcribed spacer (ITS) region rDNA partialβ-tubulin gene (TUB2) isolate MG3 amplified primers ITS4/ITS5 (White 1990) BtuF5/BtuR7a (Ellingham 2019), respectively. BLASTn analysis ITS sequence (MN833717) 100% identical many records whereas TUB2 (MW363957) record fusca (syn. xanthii; KC333362) NCBI GenBank. A pathogenicity test conducted by dusting an onto six healthy four-week-old (cv 'Tainan No. 3'). Another three inoculated used control. All maintained greenhouse 25 28°C. symptoms after 10 days, control remained symptomless. our knowledge, this report causing disease Taiwan. also has reported Thailand (Meeboon 2016), while other referring E. polygoni infecting Vigna spp. are Brazil Fiji (Farr Rossman 2020). Although have now Taiwan, species predominates more important remains unclear. comprehensive survey accurate identification required develop effective management disease, particularly resistance breeding.