The effects of host plant resistance genes and vector transmission on the evolution of resistance-breaking in tomato spotted wilt virus

Rapid evolution of resistance-breaking in plant viruses threatens the durability of crop resistance genes. Selection placed on viruses by both plant hosts and insect vectors play important roles in the emergence and continued success of resistance-breaking mutants in the population. Using a low-performing, resistance-breaking isolate of Tomato spotted wilt virus (TSWV) and the plant host, bell pepper (Capsicum annuum), it was hypothesized that repeated exposure to the Tsw+ resistance allele in pepper would lead to a highly adapted TSWV isolate. In the absence of the Tsw+ allele, it was hypothesized that resistance-breaking mutants would be lost from the population. Using mechanical inoculation, TSWV was serially inoculated in plant hosts with and without the Tsw+ resistance gene. Phenotypic expression of the virus in its host was measured and samples were collected for sequencing. Rapid evolution of TSWV in response to host genotype is evidenced by high infectivity in hosts carrying the Tsw+ resistance allele after only a couple passages. The ability to break resistance was rapidly lost after several passages in hosts without the Tsw+ allele. Major economic losses occur when resistance-breaking mutants become widespread in the population. Understanding factors that increase the prevalence of resistance-breaking mutants can lead to improved control strategies and higher durability of resistance genes.