The relative infectivities and genomic characterisation of three distinct mastreviruses from South Africa

The genomic nucleotide sequences of the cloned agroinfectious genomes of th ree South African mastreviruses obtained from Zea mays, a Setaria sp., and Panicum maximum (designated MSV-Kom, MSV-Set, and PanSV-Kar respectively), were determined. Additionally, their relative infectivities and virulence w ere analysed in a range of differentially susceptible wheat, maize, and bar ley genotypes. MSV-Kom produced moderate to severe streak symptoms in all m aize genotypes tested, but only moderate to very mild symptoms in the wheat and barley genotypes. MSV-Set infected only the susceptible to tolerant ma ize genotypes, but was generally more severe in the barley and wheat genoty pes than MSV-Kom. PanSV-Kar was incapable of infecting any of the wheat and barley genotypes and only produced very mild symptoms on the three most se nsitive maize genotypes. Genomic characteristics in common with related mas treviruses were identified. Phylogenetic analysis indicated that while MSV- Kom was closely related to previously sequenced MSV isolates, MSV-Set and P anSV-Kar represented distinctly novel strains of MSV and PanSV respectively . In the case of MSV-Set, this is the most distantly related MSV strain yet characterised.