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FIRST REPORT OF TRICHOCONIELLA PADWICKII CAUSING LEAF SPOT DISEASE ON PARTHENIUM WEED

M. Kaur, N.K. Aggarwal

Abstract


Parthenium hysterophorus is an annual or ephemeral weed causing great damage to grassland ecosystems, but also allergy and dermatitis in humans and livestock. Since the use of fungal pathogens has been suggested as a most efficient biocontrol method, a survey was conducted in 2012-2014 in the Haryana state (India), during which dark brown to black marginal spots were observed on parthenium leaves. These lesions were initially round pinpoints that enlarged and coalesced causing a premature defoliation. From symptomatic leaves collected from different areas, surface-sterilized in 70% ethanol and placed on PDA, a fungus was isolated showing an initially whitish brown aerial mycelium that turned orange- brown to purple black (Aneja et al., 2000). Conidiophores were brown, straight to geniculate (160 x 5.0-9.3 μm), bearing obclavate, rostrate, pale to golden brown 71-103×16.4-23.6 μm conidia, smooth to minutely verruculose, with 5-9 transverse but no longitudinal septa, singly or in chains of two. The conidial beak (50-172 x 1.4-3.1 μm) was hyaline, filiform, septate, straight to geniculate, sometimes swollen at the apex, often much longer than the spore body. Based on these characteristics, the fungus was identified as Trichoconiella padwickii (Ellis, 1971), as confirmed by the International Mycological Institute (IMI accession no. 502783). Pathogenicity was proven by placing seven-day-old mycelial plugs (5 mm) on detached parthenium leaves that reacted with spots from which T. padwickii was re-isolated. The ITS rDNA sequence analysed using the FASTA algorithm shared 100% nucleotide similarity to six unpublished ITS sequences from Alternaria padwickii (current name T. padwickii). This pathogen has previously been reported on rice, millet, sorghum, eucalyptus and various grasses but, to our knowledge, this is the first report on P. hysterophorus.

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DOI: http://dx.doi.org/10.4454/JPP.V97I1.040

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