The replicative fitness and virulence of potato virus Y evolve differently in pepper lines with different levels of resistance and tolerance

Despite their great agronomic interest and widespread occurrence in germplasm resources, the quantitative resistance and tolerance of plants to their parasites have rarely been studied in terms of durability potential. Using experimental evolution under controlled conditions for 9 months, we compared the evolution of potato virus Y (PVY) ( Potyvirus yituberosi ) virulence, measured by the effect of viral infection on plant fresh weight, and replicative fitness, measured by systemic viral load, in five pepper ( Capsicum annuum ) lines contrasting in their levels of quantitative resistance and tolerance. PVY evolutionary trajectories differed between pepper lines. Three lines revealed either an increase in PVY replicative fitness or an increase or decrease in PVY virulence. Two other lines did not reveal any significant change in PVY replicative fitness or virulence. The tolerance level of three pepper lines also differed significantly when measured with initial and evolved PVY populations, often associated with changes in PVY virulence. PVY evolutionary trajectories were partly explained by parameters linked to plant resistance operating at different stages of infection (inoculation, colonization of inoculated leaves and systemic infection). This study provides information on the durability potential of quantitative resistance and tolerance to PVY in pepper.