Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 15, 2003
Publication Date: June 1, 2003
Citation: Stenger, D.C., French, R.C. 2003. Population genetics of wheat streak mosaic virus provides an insight into plant virus evolution. American Phytopathological Society Annual Meeting. Phytopathology 93:(Supplement) S99. Technical Abstract: Nucleotide sequence data of wheat streak mosaic virus (WSMV) reveal the signatures of negative selection and genetic drift. The P3 gene of WSMV appears to be under tight negative selection, such that even synonymous substitutions are infrequent among divergent strains. In contrast, much more variation is evident within the coat protein (CP) gene, with the bulk of substitutions synonymous and potentially neutral with respect to fitness. Phylogenetic analysis of the CP gene of ~50 WSMV isolates from the U. S. population indicates a pattern of radial divergence from a single common ancestor. Cross-protection, spatially subdivided populations within infected plants, and transmission bottlenecks facilitate genetic isolation, and may contribute to radial divergence of WSMV lineages within a population. On the other hand, homoplasy suggests that the observed rate of mixed infections in the field (~2%) is sufficient to allow recombination among lineages. Low effective population sizes coupled with bottlenecks during cell-to-cell movement and vector transmission may facilitate fixation of nucleotide substitutions within a lineage. Laboratory studies indicate that the substitution fixation rate in a lineage is ~0.35 nt/genome/serial passage, or one fixed change per genome per three serial passages. Application of this evolution rate suggests that the present variation in the U. S. WSMV population could have arisen in about a century, a time-frame that corresponds with the introduction of wheat monoculture in the Great Plains.