Transition from common tobacco mosaic virus to the Nicotiana glauca form

Tobamoviruses as Models for the Study of Virus Evolution

The study of tobacco mosaic virus and other tobamovirus species has greatly contributed to the development of all areas of virology, including virus evolution. Research with tobamoviruses has been pioneer, or particularly significant, in all major areas of research in this field, including: the characterization of the genetic diversity of virus populations, the mechanisms and rates of generation of genetic diversity, the analysis of the genetic structure of virus populations and of the factors that shape it, the adaptation of viruses to hosts and the evolution of host range, and the evolution of virus taxa and of virus-host interactions. Many of these continue to be hot topics in evolutionary biology, or have been identified recently as such, including (i) host-range evolution, (ii) predicting the overcoming of resistance in crops, (iii) trade-offs between virus life-history traits in virus evolution, and (iv) the codivergence of viruses and hosts at different taxonomical and spatial scales. Tobamoviruses may be particularly appropriate to address these topics with plant viruses, as they provide convenient experimental systems, and as the detailed knowledge on their molecular and structural biology allows the analysis of the mechanisms behind evolutionary processes. Also, the extensive information on parameters related to infection dynamics and population structure may facilitate the development of realistic models to predict virus evolution. Certainly, tobamoviruses will continue to be favorite system for the study of virus evolution.

Association of logistic and Poisson models of infection with some physical characteristics of a single component plant virus

A logistic model was recently formulated to describe the relationship between concentration of a single component plant virus and infections produced by inoculation to a local lesion host. In this paper the logistic is combined with a Poisson model. The logistic makes accurate fitting possible for a variety of infection-dilution series; and the Poisson acts as a base line, indicating whether lesion numbers are compatible with the hypothesis that random infection of similar infection sites has occurred. A logarithmic form of the logistic equation gives a straight line with negative slope (logit slope) which is useful in characterizing dilution series to which the logistic is fitted. A modified Poisson equation can also be fitted to a range of dilution series; it provides an independent estimate of slope for curves not widely divergent from the standard Poisson. Models have also been developed to define the limits of concentration within which single virions are likely to be randomly dispersed in inoculum without immediate contact with other virions, and are therefore more likely to enter inoculated tissue independently and cause random infections. Models are formulated for aggregation of tobacco mosaic virus in monolayers, crystals, and lenticular aggregates. Published and unpublished data are fitted and analyzed using some of these models.