Resistance to Tomato mosaic virus (ToMV) in sweet pepper (Capsicum annuum L.)

Pepper (Capsicum spp.) is an increasingly important crop worldwide, and is commonly used as a vegetable, spice, and food colorant. Tobamoviruses are the most important pepper-infecting viruses that are not transmitted by an insect vector. External seed contamination, internal seed infection, and contact are the primary modes of transmission for tobamoviruses. Resistance to the different species and pathotypes of tobamoviruses in pepper is conferred by different alleles of the L-locus on chromosome 11. Tomato mosaic virus (ToMV) is one of the most widespread tobamoviruses in Southeast Asia and Southern Europe. Little is known about the L gene alleles in sweet pepper involved in resistance to ToMV strain in Taiwan. The objective of this study was to identify novel resistance sources against ToMV from available sweet pepper germplasm accessions and to determine the possible genetic basis of these resistant lines. In total, 47 advanced sweet pepper breeding lines were screened for resistance to ToMV. Susceptible symptoms included leaf mosaic, yellowing, abscission and necrotic lesions, stem lesions, and plant death. Lines were considered resistant if necrotic lesions occurred only on inoculated leaves. Eight lines from three different genetic backgrounds were identified as resistant. Accumulation of ToMV coat protein was not detected in the systemic leaves of the resistant lines, but was detected in the systemic leaves of susceptible lines. Using previously published molecular markers, we found that all of the resistant lines possessed L² allele, and two of the resistant lines also contained L⁴ gene. The resistant sweet pepper lines identified in this study displayed good horticultural traits and can serve as sources of ToMV resistance in breeding programs. Additionally, these lines may serve as potential sources of resistance to other pathotypes and species of tobamoviruses.