In India, rice (Oryza sativa L.) plays a major role in national food security, with total production of 102.75 million t, harvested from 44 million ha during 2011 (1). Weeds are one of the major causes of losses in rice. Cyperus iria, locally known as chatriwala dela (rice flat sedge), is an annual weed in the Cyperaceae that can reach 50 to 60 cm tall. A leaf blight of C. iria was observed during August 2010 in a 20-ha rice field (cv. Basmati 370) at the University Research Farm, Chatha, Jammu (32° 43′ N, 74° 54′ E). Symptomatic plants were scattered randomly in the field and had water-soaked spots on the upper leaf surfaces initially, which turned brown after 4 days and developed a yellow halo, resulting in a blighted appearance. The diseased leaves shriveled and infected plants died. Infected C. iria leaf pieces with adjacent healthy tissue were collected, surface-sterilized in 0.1% mercuric chloride for 20 s, then rinsed three times in sterilized distilled water. The pieces were plated onto potato dextrose agar (PDA) and incubated at 27 ± 1°C for 4 days. A pure fungal culture was obtained by single-spore technique on 2% water agar and maintained on PDA at 10°C. The fungus initially produced white mycelium that became brown with age. Dark brown spots or flecks of pigment formed in the agar. Macroconidia were long and slender, with tapered apical cells that were elongated or even whip-like. Basal cells of macroconidia were prominent, foot shaped, and elongated. Macroconidia were 39.55 to 56.74 × 3.75 to 4.5 μm with 3 to 5 septa. Conidiophores were compact, penicillately branched, and arose from lateral branches which initially were one-celled and bore 2 to 4 phialides at the apex. Chlamydospores were intercalary, solitary, in chains or in knots, globose, and 7 to 9 μm in diameter. On the basis of morphological characteristics (2), the fungus was identified as Fusarium equiseti (Corda) Sacc. and deposited in the Indian Type Culture Collection, New Delhi (8424.11). The ITS (internal transcribed spacer) region of rDNA was amplified by PCR with primers ITS1/ITS2 and sequenced. BLASTn analysis of the sequence showed 100% homology with the ITS sequence of F. equiseti in the NCBI database (JN596252.1), and the sequence was deposited in GenBank (KC434458). To confirm pathogenicity of the F. equiseti isolate, 10 seeds of C. iria were planted in five clay pots (each 38 cm in diameter) filled with sterilized soil. Three seedlings were used for the experiment and the remaining seedlings removed from each pot. A total of 15 seedlings (5 pots × 3 seedlings per pot) at the two-leaf stage were spray-inoculated with a 50-ml conidial suspension of the isolate (105 cfu/ml) using a hand atomizer. The control treatment included three seedlings treated similarly with sterile distilled water. The spore suspension was prepared in potato dextrose broth using a culture of the fungus incubated for 10 days and then homogenized at 140 rpm. Tween 20 (1%) was added to the spore suspension. Small spots developed 4 days after inoculation, and the lesions then coalesced into large necrotic areas, resulting in leaf blight 10 days after inoculation. F. equiseti was reisolated from inoculated leaves using the method described above, whereas no fungus was reisolated from control plants, fulfilling Koch's postulates. The isolated fungus displayed the same morphological and cultural features as the original isolate. F. equiseti has been reported to infect Echinochloa spp. in Iran (3), but to our knowledge, this is the first report of F. equiseti infecting C. iria in India. Thus, F. equiseti represents a potential biocontrol agent for managing C. iria in rice fields.
References: (1) Anonymous. Direct. Rice Res. Newslett. 10:2, 2012. (2) C. Booth. The Genus Fusarium. Commonwealth Mycological Institute, Kew, Surrey, England, p. 157, 1971. (3) M. R. S. Motlagh. Austral. J. Crop Sci. 4:457, 2010.