VARIABILITY AND GENETIC STRUCTURE OF PLANT VIRUS POPULATIONS

Abstract

Populations of plant viruses, like all other living beings, are genetically heterogeneous, a property long recognized in plant virology. Only recently have the processes resulting in genetic variation and diversity in virus populations and genetic structure been analyzed quantitatively. The subject of this review is the analysis of genetic variation, its quantification in plant virus populations, and what factors and processes determine the genetic structure of these populations and its temporal change. The high potential for genetic variation in plant viruses, through either mutation or genetic exchange by recombination or reassortment of genomic segments, need not necessarily result in high diversity of virus populations. Selection by factors such as the interaction of the virus with host plants and vectors and random genetic drift may in fact reduce genetic diversity in populations. There is evidence that negative selection results in virus-encoded proteins being not more variable than those of their hosts and vectors. Evidence suggests that small population diversity, and genetic stability, is the rule. Populations of plant viruses often consist of a few genetic variants and many infrequent variants. Their distribution may provide evidence of a population that is undifferentiated, differentiated by factors such as location, host plant, or time, or that fluctuates randomly in composition, depending on the virus.

Genetic diversity and biological variation among California isolates of Cucumber mosaic virus

“…However, the genetic variation of CMV observed here was not correlated with geographic region, collection date or plant species. This is similar to the population structure of CMV described in Spain, where the genetic structure of 17 CMV subpopulations was not correlated with location or year, but showed a metapopulation structure with local extinction and random recolonization from local or distant virus reservoirs (Fraile et al, 1997;Garcia-Arenal et al, 2001). …”

Genetic diversity of the coat protein of olive latent virus 1 isolates

“…Low CP sequence diversity (0.03 -0.10) has been observed for other RNA viruses [16]. Similar studies on other members of the family Tombusviridae, (carnation mottle virus [3] and pelargonium flower break virus [31]) have measured diversity values for CP sequences of & 0.03.…”

Sequence diversity and potential recombination events in the coat protein gene of Apple stem pitting virus

“…Similar high levels of CP gene diversity are described for other members of the family Betaflexiviridae (Alabi et al, 2010;Teycheney et al, 2005). The lack of a biological vector for transmission of ASPV probably makes the CP more tolerant to sequence variability than the capsid proteins of vector borne plant viruses subjected to greater purifying selection on amino acid changes (Garcia-Arenal et al, 2001;Rubio et al, 2001;Vives et al, 2002).…”