Molecular identification of Maize streak virus reveals the first evidence for a subtype A1 isolate infecting maize in Cameroon

Maize streak virus (MSV; genus Mastrevirus) causes significant damage to maize (Zea mays) in Africa. To date, only strain A of MSV has been associated with maize streak disease in Africa (Varsani et al., 2008). In Cameroon, maize streak is thought to be one of the most important maize diseases. It occurs routinely in the Western Highlands at a reported incidence of 20-50% (Cardwell et al., 1997; Ngoko et al., 2001), and at approximately 90% incidence in 2007. To confirm the presence of MSV and to identify the strain, leaf samples were collected from three symptomatic maize plants in Bambui, North West Province, Cameroon (Fig. 1). The samples were pressed and dried, and the DNA was extracted using Extract-n-Plant PCR (Sigma) (Shepherd et al., 2008). Extracts were subjected to rolling cycle amplification (RCA). Digestion of the single RCA product with either BamHI or KpnI yielded an expected size fragment of ~2.7 kb. The BamHI or KpnI fragments from one sample were cloned and the DNA sequence for each was determined bi-directionally. The sequences were 2689 nucleotides in length, and were identical (GenBank Accession No. FM210279).

A BLAST search of GenBank revealed the highest nucleotide identity, at 99%, to two Nigerian subtype A1 isolates from native grasses, MSV-A1[NG:Abe:07] (EU628566) and MSV-A1[NG:Ile:07] (EU628567), and with the Kenyan maize isolate MSV-A1[KE:Ama:98] (AF329878). Phylogenetic analyses with representative MSV strains and subtypes further supported classification of the Cameroon isolate (MSV-A1[Cameroon: Bambui: 2008]) to subtype MSV-A1 (Fig. 2). This is the first molecular evidence for MSV in Cameroon, and the first report of an A subgroup isolate there.