he best attack does not always start by a good defense: Higher plant tolerance/resistance may be an evolutionary advantage for viruses

When colonizing an ecosystem, in general plant viruses encounter host plants with different types (resistance or tolerance) and degrees (total or partial) of plant defenses. Little is known on how viruses adapt to these heterogeneous environments despite being a key factor for the success of disease outbreaks. Dr. Israel Pagán´s group investigated this question by monitoring the evolution of Turnip mosaic virus in populations of its natural host Arabidopsis thaliana with different proportions of individuals tolerant to infection. The results of this study indicate that, in the absence of tolerant individuals in the host population, the virus evolves to reduce their within-host multiplication (higher plant resistance) and virulence. This in turn increases plant lifespan and consequently the chances for the virus to be transmitted. On the other hand, in populations composed only by tolerant individuals, virus evolution increases plant tolerance by enhancing virus within-host multiplication at no (or little) cost on plant mortality, which again benefits virus transmission. In sum, this research provides novel information on the processes of virus adaptation to the host defenses at the population, rather than at the individual, level. Also, and at odds with what could be intuitively expected, results show that more effective plant defenses are not necessarily detrimental for viruses, which has relevant implications for the development of control measures in crops.