First report of Boeremia exigua var. exigua as a pathogen of Cycas circinalis in India
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First report of Boeremia exigua var. exigua as a pathogen of Cycas circinalis in India Arghya Banerjee 1 & Birendranath Panja 1 Received: 31 October 2019 / Accepted: 29 January 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Abstract In late summer 2016, necrotic lesions on leaves were observed on Cycas circinalis L. plants, in the Agri-Horticultural Society of India, Alipore Road, Kolkata (located at 22˚53'N; 88°33' E), West Bengal. Based on morphology, DNA sequencing and pathogenicity testing the causal pathogen was identified as Boeremia exigua var. exigua, which is the first report on C. circinalis in India. Keywords Phoma . Fungal plant disease . Leaf necrosis . Palm
Cycas circinalis L. (Cycadaceae), an economically important ornamental house plant, grows throughout the world including India. It has separate significance in agri-horticultural economic enterprises due to its ornamental values, medicinal properties, industrial use and oil production capacities. In late summer 2016, necrotic lesions on leaves were observed on C. circinalis plants, in the Agri-Horticultural Society of India, Alipore Road, Kolkata (located at 22°53’N; 88°33′ E), West Bengal. Typical tip and marginal drying of leaves surrounded by light brown to ashy straw margin followed by spindle to circular shaped dense brown zonation were the characteristic symptoms of the disease. Microscopic examination of the affected tissue revealed the presence of irregularly scattered globose pycnidia (80–200 μm wide) with a distinct ostiolum. Conidia were hyaline, ellipsoid, occasionally one-septate, and measured 6.5 (4.5–8) × 2.5 (2–4) μm. Chlamydospores were highly variable in shape and dimensions, occasionally solitaryterminal, but usually in branched or unbranched chains, hyaline, thick walled, mostly oval and smooth. Necrotic lesions were surface disinfected (1 min in 2% NaOCl), plated onto water agar (WA) and incubated at room temperature. Isolated colonies produced scarce pycnidia of a Boeremia species. On
the basis of the characters in vitro on peptone salt agar (PSA), oat meal agar (OMA) (Boerema et al. 2004), the pathogen was initially identified as Boeremia exigua Desm. Genomic DNA was extracted from mycelia of the isolated fungus using the CTAB method and the internal transcribed spacer (ITS) region of rDNA was amplified using ITS1 (5’-TCCGTAGG TGAACCTGCGG-3′) and ITS4 (5′- TCCTCCGCTTATTG ATATGC-3′) primers (White et al. 1990). The raw sequence was assembled with MEGA 7.0 and the consensus sequence deposited in GenBank ( Accession No. MK584540). The sequence was identical to Boeremia exigua ITS sequences in GenBank (Altschul et al. 1997). Pathogenicity tests were performed by spraying leaves (n = 10) of attached lateral shoots with a spore and mycelial suspension (2 × 106 CFU/ml) in greenhouse condition. Control leaves were sprayed with sterile water. The first symptoms developed on leaves six days after inoculation. The fungus was re-isolated with sterile water from the lesions on leaves. Leaflet blight or die
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