Dating the origins of the maize-adapted strain of maize streak virus, MSV-A.

Gordon W Harkins,Oliver P Windram,Tania Van Antwerpen,Michel Peterschmitt,Darren P Martin,Siobain Duffy,Moses Ramusi,Dionne N Shepherd,Rizwan A Sayed,Arvind Varsani,Edward P Rybicki,Bradley Flett,Lara Donaldson,Betty E Owor,Aderito L Monjane

doi:10.1099/vir.0.015537-0

Abstract

Maize streak virus (MSV), which causes maize streak disease (MSD), is one of the most serious biotic threats to African food security. Here, we use whole MSV genomes sampled over 30 years to estimate the dates of key evolutionary events in the 500 year association of MSV and maize. The substitution rates implied by our analyses agree closely with those estimated previously in controlled MSV evolution experiments, and we use them to infer the date when the maize-adapted strain, MSV-A, was generated by recombination between two grass-adapted MSV strains. Our results indicate that this recombination event occurred in the mid-1800s, ∼20 years before the first credible reports of MSD in South Africa and centuries after the introduction of maize to the continent in the early 1500s. This suggests a causal link between MSV recombination and the emergence of MSV-A as a serious pathogen of maize.

Highlights

Maize streak virus (MSV; family Geminiviridae, genus Mastrevirus) is amongst the most important plant patho-The GenBank/EMBL/DDBJ accession numbers for the genome sequences of the MSV isolates analysed in this study are FJ882089– FJ882124 and FJ882126–FJ882149
The mean substitution rates estimated for the full genome and mostly recombination-free MPCP datasets with the various clock and demographic models tested were broadly similar and ranged from 1.861024 subs per site per year to 3.961024 subs per site per year
The Bayes factor (BF) tests significantly supported models enforcing relaxed over strict molecular clock models (Table 1; note that 2lnBF scores .3 reflect a significantly better fit of model H1 versus H0)

Summary

Introduction

The GenBank/EMBL/DDBJ accession numbers for the genome sequences of the MSV isolates analysed in this study are FJ882089– FJ882124 and FJ882126–FJ882149. Whereas MSV is best known for causing occasionally devastating maize streak disease (MSD) epidemics throughout sub-Saharan Africa, it infects over 80 other species, primarily wild grasses in the family Poaceae (Damsteegt, 1983; ICTVdb Management, 2006; Konate & Traore, 1992). Of the 11 known MSV strains (Varsani et al, 2008) only one, MSV-A, is usually found infecting maize plants. ‘Grass-adapted’ strains such as MSV-B, -C, -D and -E cannot symptomatically infect any but the most MSV-susceptible maize genotypes (Martin et al, 2001; Schnippenkoetter et al, 2001; Willment et al, 2002)

Methods

Results

Conclusion