Arch Virol (2001) 146: 619–628
Contributions of genetic drift and negative selection
on the evolution of three strains of wheat streak
, J. S. Hall
, L. Zhang
, G. L. Hein
, and D. C. Stenger
USDA-ARS and Department of Plant Pathology, University of Nebraska,
Lincoln, Nebraska, U.S.A.
Centro Internacional De Mejoramiento de Maiz y Trigo,
Mexico City, Mexico
Department of Entomology, University of Nebraska Panhandle Research
and Extension Center, Scottsbluff, Nebraska, U.S.A.
Accepted August 2, 2000
Summary. Genome sequences of three Wheat streak mosaic virus (WSMV)
strains were compared. The Type and Sidney 81 strains of WSMV from the
American Great Plains were closely related, with sequence identities of 97.6%
(nucleotide) and 98.7% (amino acid). In contrast, the El Batán 3 strain from central
Mexico was divergent, and shared only 79.2–79.3% (nucleotide) and 90.3–90.5%
(amino acid) sequence identity with Type and Sidney 81. All three WSMV strains
were serologically related, however the El Batán 3 capsid protein (CP) had 15
fewer amino acid residues. Phylogenetic analysis of the CP cistron indicated that
Type, Sidney 81, and nine other American isolates of WSMV were closely re-
lated and distinct from the El Batán 3 sequence. Nucleotide substitutions among
the WSMV strains were not randomly distributed across the genome with more
variation within P1, HC-Pro, and CP, and less within P3. One 400-nucleotide
region of the genome, corresponding to the 3
-end of P3, was strikingly deﬁcient
in silent substitutions. Nonetheless, the ratio of synonymous to non-synonymous
substitutions throughout the genome wasessentially the same for all three WSMV
strains. Collectively, our data indicate that both genetic drift and negative selec-
tion have contributed to the evolution of WSMV strains.
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