# What makes a host a good reservoir? Determinants of the reservoir potential of Nicotiana glauca for tobacco mild green mosaic virus

## TL;DR

The study explores why Nicotiana glauca is a good reservoir for a virus that affects pepper crops, revealing traits like low virulence and seed transmission that help maintain the virus.

## Contribution

The study identifies how conditional mutualism and pleiotropic effects of mutations maintain virus reservoir potential in wild plants.

## Key findings

- TMGMV is maintained at high prevalence in Nicotiana glauca populations near pepper crops.
- Low virulence and increased plant survival under drought explain high prevalence.
- Pleiotropic effects of mutations enhance virus transmission through N. glauca seeds.

## Abstract

Identifying traits that make a host a good reservoir for virus emergence is central to understanding virus ecology, host range evolution and mitigating virus epidemics, but is often hindered by a lack of knowledge on the infection dynamics of the virus in the reservoir population. Here we analyse traits that determine the reservoir potential of the wild plant Nicotiana glauca for tobacco mild green mosaic virus (TMGMV), an important pathogen of pepper (Capsicum annuum) crops, using epidemiological, experimental and population genetic approaches. We show that TMGMV is maintained at high prevalence in N. glauca populations that share the space with pepper crops in South eastern Spain. High prevalence may be explained by low virulence associated with TMGMV behaving as a conditional mutualist, which is in part explained by increased survival of infected plants under drought conditions. We also show maintenance in N. glauca populations of TMGMV genotypes that have a within-host fitness advantage in pepper and a disadvantage in N. glauca. This is explained by pleiotropic effects of host range mutations that result in higher vertical transmission through the seeds of N. glauca of isolates adapted to pepper. Last, high migration from N. glauca prevents fixation of pepper-adapted genotypes in pepper populations. Our results underscore the need to analyse the effects of infection on a range of host life-history traits, and effects of host range mutations on different components of virus fitness, to understand dynamics of infection and virus host range evolution.