T. Farhana, R.L. Wick, M.T. Islam
doi: 10.4454/JPP.V98I1.024
Annual vinca (Catharanthus roseus), also known as Madagascar periwinkle, is native to the island of Madagascar, and now common in many tropical and subtropical regions worldwide, including Bangladesh (Chevallier, 1996). It has long been cultivated for herbal medicine and as an ornamental plant. Symptoms of stem canker and leaf blight developed on C. roseus in a landscape planting at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh, in June, 2014. To identify the pathogen, infected leaves were placed in water for 48 h, then the mycelia were transferred onto corn meal agar plates. Mycelial growth was patchy and irregular, coenocytic and tufted with an arachnoid branching habit, consistent with descriptions of Phytophthora nicotianae. The pathogen was also cultured on PARP medium (Ferguson and Jeffers, 1999) and V8 agar medium and pure cultures were established. Mycelial blocks (6 mm in diameter) were placed in sterile water for 3 days, then at 5 ̊C for 15 min in the dark to stimulate production of sporangia and zoospores. Molecular identification was done by amplifying the ITS region of nuclear rDNA using ITS 4 and ITS 6 primer pairs. BLAST search revealed that the isolate had 100% identity with P. nicotianae (GenBank accession No. KT175508.1). The nucleotide sequence was deposited in GenBank under accession No. KU244700. Pathogenicity tests were conducted by inoculating Catharanthus leaves, previously wounded by pricking with a sterile needle, with 50 μl and 100 μl aliquots of zoospores. Foliar symptoms consistent with blight observed in the field developed on all the inoculated leaves after 72 h. Koch’s postulates were fulfilled by re-isolating the pathogen from the lesions on the inoculated leaves. To our knowledge, this is the first molecular identification of P. nicotianae on Catharanthus in Bangladesh.