First Report of Curvularia penniseti Causing Leaf Blight of Bajra Napier Hybrid Grass in India

Abstract

Bajra Napier hybrid (Pennisetum glaucum x Pennisetum purpureum) is a perennial, high yielding grass and is widely grown for fodder in India. During August-2021, Bajra Napier hybrid germplasm line (NBN 15-2) showed severe leaf blight symptoms at ICAR-Indian Grassland and fodder research institute, Jhansi (25.527890 N, 78.5451400 E). Symptoms were initial irregular yellow spots on the leaf lamina, which later became brownish, coalesced and gave blighted appearance to the leaf surface. Disease severity recorded was 55 to 60 percent. To isolate the pathogen, 10 symptomatic leaf samples were cut into small pieces (~4 mm2), surface-sterilized with 70% ethanol for 30 seconds and rinsed with sterile water. Sterilized leaf pieces were transferred to potato dextrose agar (PDA) and incubated at 28°C for 7 days. Four similar fungal isolates (BNHCP-1 to BNHCP-4) were obtained from the affected portions. The colonies were grayish-brown with dark brown margins. Conidia were mostly clavate, elongated, straight or bent at the terminal cell, with 2-3 septa with dimensions of 17.5 to 30 μm × 10 to 12.5 μm (avg. 24 μm × 12 μm; n=40). The third cell from the base was broader and darker. These morphological characteristics were consistent with previous descriptions of Curvularia penniseti (Mitra) Boedijn (Ellis, 1971). To confirm the species, BNHCP-1 was chosen as representative isolate for further studies. Internal transcribed spacer (ITS) region and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene of isolate BNHCP-1 was amplified with primers ITS1F/ITS4R (White et al. 1990) and GDF/GDR (Templeton et al. 1992), and sequenced. The sequences were deposited in GenBank (ITS: OM073980; GAPDH: OM103702.2). BLASTn analysis showed 99.6% and 98% similarity of ITS and GAPDH gene respectively with GenBank accession numbers MH859833.1 (548 bp/550 bp) and MN688838.1 (130 bp/133 bp) of C. penniseti. A maximum-likelihood phylogenetic analysis based on concatenated sequences of ITS and GAPDH gene using MEGA X placed the isolate BNHCP-1 within a clade comprising C. penniseti. Pure culture of BNHCP-1 was deposited in National Agriculturally Important Microbial Culture Collection (NAIMCC), Maunath Bhanjan (Uttar Pradesh) with accession number NAIMCC-F-04251. For pathogenicity, root slips of Bajra Napier hybrid germplasm line NBN 15-2 were transplanted in pots (6 pots; 2 root slips per pot) and kept for fresh growth in a growth chamber at 25 0C for 21 days. Bajra-Napier hybrid plants were sprayed until runoff with conidial suspension (5 × 105 conidia/ml) made from 2-week old fungal colony grown on PDA petri dish. The pots were covered with plastic bag for 48 h to maintain humidity. Inoculated plants displayed small, brown, oval-shaped lesions within seven days on the lamina and edges of the leaf which later enlarged and gave blighted appearance to the leaf. Control plants were asymptomatic. The pathogen was re-isolated from the inoculated leaves and confirmed morphologically, fulfilling Koch’s postulates. C. penniseti has been reported earlier from Pennisetum americanum, P. clandestinum, Sorghum and Triticum sp. from different parts of the world (Sivanesan, 1987). However, there is no report of C. penniseti in Bajra Napier hybrid. Thus, to the best of our knowledge, this is the first report of C. penniseti from Bajra-Napier hybrid grass in India. Further studies on economic impact of this disease on Bajra-Napier hybrid production and its presence on commercial cultivars are needed.