First Report of Johnsongrass mosaic virus Infecting Urochloa mosambicensis in Ethiopia

Abstract

Urochloa mosambicensis (Hack.) Dandy, commonly known as sabi grass, is a perennial grass with a creeping and stoloniferous habit. Predominantly used as a cereal in southern Africa, sabi grass is also commonly used for a variety of purposes including forage for livestock production, protection against soil erosion, and in the rehabilitation of mine sites. Its fast-growing nature combined with drought resistance, salinity tolerance, ability to grow on different soil types, fertility levels and environments, tolerance to heavy grazing, and good seed production capacity all help to demonstrate that it has great potential as a pasture grass for the semiarid tropical regions. The Forage Genebank of the International Livestock Research Institute in Ethiopia maintains a total of seven accessions of Urochloa germplasm at their field site in Zwai, on the border of Oromia and the Southern Nations, Nationalities, and Peoples regions. During routine disease surveillance of the field, a typical mosaic symptom was observed on some of the Urochloa accessions. Consequently, both symptomatic and asymptomatic leaf samples from all accessions were collected and tested for virus infection by dot-blot assay using in-house antisera developed to detect two strains (Is-14982 and Is-16840) of Elephant grass mosaic virus (Mih and Hanson 2004) and a Brachiaria potyvirus antiserum received from the International Center for Tropical Agriculture, Colombia. Two accessions of U. mosambicensis (7233, 16665) that showed significant mosaic symptoms produced a positive reaction with the Brachiaria potyvirus antiserum and a weak reaction with the antiserum to Is-14892; one accession (16665) that showed minor symptoms produced a weak reaction only with the antiserum to Is-16840 and not with the Brachiaria potyvirus antiserum; and the other four asymptomatic accessions did not give any reaction with any of these antisera. The association of virus only with two accessions (7233, 16665) of U. mosambicensis was further confirmed by reverse-transcription (RT) PCR using a pair of universal primers, NIb2F/NIb3R designed for potyvirus (Zheng et al. 2010). The initial BLAST analysis of the sequences generated by direct sequencing of both the PCR products indicated the presence of Johnsongrass mosaic virus (JGMV) in these grass accessions. For more accurate determination of the associated virus, a pair of JGMV-specific primers; GBV125F (5′-GGAACAACCGTCTATCTGACG-3′) and GBV106R (5′-GTGGTGAGAAGCTCACTCTTA-3′) were designed to conserved domains flanking the viral coat protein (CP) gene, using the sequences available in the NCBI database. RT-PCR analysis produced a specific ∼1.5 kb amplification product indicative of JGMV in both accessions, and the PCR product from accession 7233 was then fully sequenced. A pairwise comparison of the CP sequences of the present isolate, ZG-181 (GenBank accession no. KY659307) with other JGMV isolates from the NCBI database showed the sequence shared 87.6 and 87.9% amino acid sequence identity with Brazilian isolates from Panicum maximum (KT289893) and Pennisetum purpureum (KT833782), respectively. A phylogenetic analysis of the available JGMV CP sequences separated the present isolate together with the Brazilian isolates of JGMV in a cluster that was distinct from the cluster formed by isolates from Australia and the United States. This study confirms the presence of JGMV in an important grass species in Ethiopia; JGMV could also pose a threat for other forage grasses and crops, and therefore this finding needs to be studied further to understand the potential impact. To the best of our knowledge, this is the first report of JGMV infection in U. mosambicensis in Ethiopia.