HYPERSENSITIVE RESISTANCE TO TOMATO SPOTTED WILT VIRUS IN 3 CAPSICUM CHINENSE ACCESSIONS IS CONTROLLED BY A SINGLE-GENE AND IS OVERCOME BY VIRULENT-STRAINS

The resistant reaction to tomato spotted wilt virus (TSWV) was found t o be determined by a single dominant gene in three Capsicum chinense J acq. accessions ('PI 152225', 'PI 159236','7204'). Allelism studies in dicated 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 l esions followed by abscission of the inoculated organ. However, a smal l proportion of them showed late systemic infection. Nine TSWV isolate s obtained from these individual plants with systemic symptoms were ba ckinoculated to the three resistant parents. All isolates were able to infect systemically all the resistant accessions without inducing loc al necrotic lesions. Serological analysis confirmed that these nine vi ral isolates belong to the TSWV species (serogroup I). Consequently, t he susceptible plants in the allelism tests could not be interpreted a s 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.