Hypersensitive resistance to tomato spotted wilt virus in three Capsicum chinense accessions is controlled by a single gene and is overcome by virulent strains
Résumé
The resistant reaction to tomato spotted wilt virus (TSWV) was found to be determined by a single dominant gene in three Capsicum chinense Jacq. accessions ('PI 152225', 'PI 159236','7204'). Allelism studies indicated that all C. chinense lines bear the same allele located at the Tsw locus. All the inoculated plants in the allelism tests displayed a resistant hypersensitive phenotype characterized by necrotic local lesions followed by abscission of the inoculated organ. However, a small proportion of them showed late systemic infection. Nine TSWV isolates obtained from these individual plants with systemic symptoms were backinoculated to the three resistant parents. All isolates were able to infect systemically all the resistant accessions without inducing local necrotic lesions. Serological analysis confirmed that these nine viral isolates belong to the TSWV species (serogroup I). Consequently, the susceptible plants in the allelism tests could not be interpreted as possessing a recombinant genotype because of the virulence change in the viral strain. Hobbs et al. (1994) already reported the existence of TSWV pathotypes overcoming the resistance of C. chinense resistant accessions. Practical consequences for pepper breeding associated with the emergence of these resistance-breaking isolates are discussed.