FIRST REPORT OF POWDERY MILDEW CAUSED BY OIDIOPSIS HAPLOPHYLLA ON EUPHORBIA HETEROPHYLLA IN INDIA
A.K. Nayak, B.K. Babu
Euphorbia heterophylla, an annual herbaceous weed in the family Euphorbiaceae, grows mainly in tropical and subtropical climates. In between October and December 2015, powdery mildew efflorences were observed on both sides of the leaves of E. heterophylla plants in different wasteland areas of the Odisha State (India). Initial symptoms were chlorotic lesions, which later became angular and necrotic. Over time, leaves were covered with a whitish powdery mycelium which was more abundant on the abaxial portion of the blade. To identify the fungal pathogen, fresh conidia were scraped from the leaf surface and observed under a light microscope. Conidia were dimorphic, 13- 17×60-88 µm in size and lacked distinct fibrosin bodies. Conidiophores were hyaline, septate, cylindrical, measured 4.5-7 × 240-320 µm, and produced single conidia, followed by 2-3 straight cells. These morphological features and measurements agree with the description of Oidiopsis haplophylla (Braun, 1987; Braun et al., 2002). To prove pathogenicity, an infected leaf was pressed on young leaves of five healthy potted E. heterophylla plants. Non inoculated plants were used as control. Plants were maintained in a greenhouse at 25-27ºC. Five to seven days post inoculation, typical white patches similar to those observed on naturally infected plants appeared on the inoculated leaves, whereas control plants remained symptomless. To the best of our knowledge, this is the first report of O. haplophylla causing powdery mildew on E. heterophylla in India.