English Lavender (Lavandula angustifolia Mill.) has been considered an alternative crop to tobacco in Hatay Province of Turkey because of its great production potential. As a new, nonnative crop, diseases and pests of lavender are not well known in the region. In summer 2010, root rot symptoms were observed with an average incidence of 45% in a 2-year-old lavender nursery in Hatay. Initial symptoms of chlorosis and wilting were followed by progressive death of the plants starting at the shoot tips. An oomycetous species was isolated consistently from the stems and roots of diseased plants on potato dextrose agar (PDA) amended with several fungicides and antibiotics. The culture of the single-zoospore isolate produced arachnoid growth on PDA. Chlamydospores of the isolate were approximately 35.0 μm in diameter. The isolate produced papillate, caduceus, hyaline sporangia in different shapes ranging from spherical to ellipsoidal. Sporangia with short pedicels (5 μm) were 35.0 to 57.5 × 27.5 to 42.5 μm with a length/width ratio of 1.2 to 1.8. On the basis of symptoms and morphology of the organism, the pathogen was identified as Phytophthora palmivora (E.J. Butler) E.J. Butler (3). Identification of the isolate was also confirmed by comparison of the sequence of the nuclear ribosomal internal transcribed spacer (ITS) region with reference isolates. The ITS region of rDNA was amplified by PCR with primers ITS1/ITS4 and sequenced (GenBank Accession No. JF777117). BLAST analysis of the sequence obtained showed a 99 to 100% homology with P. palmivora. Pathogenicity tests were performed on 12 greenhouse-grown 2-year-old lavender plants in 2-liter pots containing a steamed sand/peat/soil mixture. After rooting, the plants were inoculated by placing mycelial plugs from a 1-week-old culture of the isolate into an incision made at the base of each plant. Control plants were treated with plugs of sterile PDA. Inoculated plants were kept at 27°C for 5 weeks. Similar symptoms developed on the inoculated plants within 4 weeks after inoculation. P. palmivora was consistently reisolated from symptomatic plants. No symptoms developed on control plants. P. palmivora attacks a wide range of crop species including lavenders (1,2,4). To our knowledge, this is the first report of a root rot caused by P. palmivora, a new pathogen of lavender in Turkey.
References: (1) S. Davino et al. Plant Dis. 86:561, 2002. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) D. J. Stamps. C.M.I. Descr. Fungi Bact. 831:1, 1985. (4) G. A. Torres et al. Plant Dis. 94:1163, 2010.