Js. Hall et al., Three distinct mechanisms facilitate genetic isolation of sympatric wheat streak mosaic virus lineages, VIROLOGY, 282(2), 2001, pp. 230-236
Cross-protection and vector transmission bottlenecks have been proposed as
mechanisms facilitating genetic isolation of sympatric viral lineages. Mole
cular markers were used to monitor establishment and resolution of mixed in
fections with genetically defined strains of wheat streak mosaic virus (WSM
V). Two closely related WSMV strains from the U.S. (Type and Sidney 81) exh
ibited reciprocal cross-protection in wheat, confirming this classic phenom
enon as a mechanism of genetic isolation. In contrast, cross-protection bet
ween either U.S. strain and the divergent El Batan 3 strain from Mexico was
unilateral, erratic, and only partially effective. Distribution of WSMV st
rains within individual leaves of plants supporting a mixed infection of Ty
pe and Sidney 81 was spatially nonuniform. Strain distribution among indivi
dual tillers of coinfected plants also was heterogeneous, with some contain
ing either Type or Sidney 81 alone and some containing both. Transmission b
y wheat curl mites, acquiring virus from source plants simultaneously infec
ted with both Type and Sidney 81, often resulted in test plants bearing onl
y a single WSMV strain. Spatial subdivision of virus strains within coinfec
ted plants likely contributed to vector transmission bottlenecks during acq
uisition. Collectively, these three distinct mechanisms enhance genetic iso
lation of individual viral lineages, and together with stochastic processes
, may explain generation and maintenance of genetic diversity in field popu
lations. (C) 2001 Academic Press.