Archivio Journal of Plant Pathology

Abstract:

In April 2014, typical symptoms of downy mildew were observed on fenugreek (Trigonella faenum-graecum) plants grown in the Tabas region (Iran). A white to dark-gray mycelim was visible on the lower surface of the leaves, associated with chlorotic spots on the upper leaf surface. Conidiophores were hyaline, they branched dichotomously 6 to 10 times and measured 270-510 (average: 432) μm in length. The slightly brown, oblong to ellipsoidal conidia measured 22.5-30×17.5-20 μm (average: 26.3x18.8 μm). Oospores were yellow-brown, globose, and measured 30-42.5 μm (average 34.5 μm), whereas oogonia were globose, subglobose to irregular, 45-65 μm (average: 57 μm) in diameter. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS4/ITS5 and sequenced (GenBank accession No. KJ881163). BLAST analysis (Altschul et al., 1990) showed 100% similarity with the comparable sequence of Peronospora trigonellae (GenBank accession No. GQ421459). For pathogenicity tests, the foliage of healthy fenugreek plants was sprayed with a suspension of sporangia. Inoculated plants were incubated a moist chamber at 18-20°C and 80-90% relative humidity for two days, then moved into a greenhouse. Twelve days post inoculation, typical symptoms of mildew developed on the inoculated but not on the control plants, thus fulfilling Koch’s postulates. Downy mildew of fenugreek has previously been reported from Algeria, India, Pakistan, UK and USA (Rooney-Latham et al., 2009), but not from Iran where, to the best of our knowledge, this represents its first record.