Akademik Veri Yönetim Sistemi
Plant Disease, cilt.101, sa.10, ss.1827, 2017 (SCI-Expanded)
Garden cress (Lepidium sativum L.) is an edible herb, which is commercially cultivated in Asia and Europe. This crop is a popular vegetable used in salads, but is also used widely as a folk medicine for various ailments (Duke 2002). In March 2016, typical downy mildew symptoms were observed on leaves, stems, and fruit parts of garden cress in many cultivated fields and private farms in Hatay Province of Turkey. The disease incidences were 38.2% in 23 fields and 27.1% on 32 farms. In some commercial fields, more than 65% of plants withered or died before harvesting, and even weakly infected ones were unmarketable due to signs of senescence and withering of leaves. Initial symptoms began as a slight discoloration of the leaves that then developed into vein-limited yellow spots on the upper leaf surface and a typical white downy growth on the corresponding lower surface. A representative specimen was deposited in the Korea University Herbarium (KUS-F29456). Conidiophores were tree-like, hyaline, 110 to 325 µm long, 5.0 to 7.5 µm wide, and branched 3 to 4 times (n = 50). The ultimate branchlets were slightly curved to sigmoid, 5 to 24 µm long (n = 30). Conidia were hyaline, ellipsoidal, 20 to 23 µm wide, 25 to 40 µm long, with an apiculate tip (n = 50). Oogonia were irregular to broadly globose, 40 to 55 µm in diameter (n = 30). Oospores were globose, 32 to 38 µm in diameter, uniformly 1.5 to 2.5 µm thick wall (n = 30). The morphological measurements match with those of Perofascia lepidii (Constantinescu and Fatehi 2002). Previously, Hyaloperonospora parasitica (formerly under Peronospora) has often been considered a causal agent of downy mildew on Lepidium spp., but the present isolate is morphologically distinct from the genus by possessing ellipsoidal conidia with an apiculate tip and appressed branches. To confirm the morphological identification, both ITS rDNA and the cytochrome oxidase II (cox2) mtDNA were amplified and directly sequenced (Choi et al. 2015). The resulting sequences were deposited in GenBank (KY888669 for ITS, KY962511 for cox2). A BLASTn search revealed that the Turkish isolate is identical with the ITS sequences of P. lepidii on L. ruderale (AY531467, AY531468), and differs at one nucleotide position with GenBank cox2 sequences (KJ654166, DQ365713). Pathogenicity was confirmed through inoculation by gently dusting conidia onto the lower surface of leaves of five healthy potted garden cress plants (cv. Deniz) that were kept in a greenhouse at 22°C. Five noninoculated plants served as controls. Inoculated plants developed signs and symptoms after 7 days, whereas the control plants remained symptomless. The oomycete present on the inoculated plants was morphologically identical to the original one observed on the diseased plants, fulfilling Koch’s postulates. To our knowledge, this is the first report of downy mildew caused by P. lepidii on garden cress in Turkey. Previous reports list P. lepidii occurring on several Lepidium spp. in several countries of Europe, America, and Southeast Asia (Farr and Rossman 2017). Considering the increasing demand of this crop and the rapid transmission of this disease, it poses a serious risk to cultivation of garden cress in Turkey.