The dominant immune receptors encoded by Tsw in pepper and Sw-5b in tomato provide effective resistance against tomato spotted wilt virus (TSWV), but their durability is threatened by resistance-breaking variants. Whereas several substitutions in the viral movement protein NSm have been associated with Sw-5b resistance breakdown, the sequence variation underlying escape from Tsw -mediated recognition remains less clearly resolved. We investigated three pepper-associated TSWV isolates collected from geographically distinct regions of Texas, USA, using whole-genome sequencing, phylogenetic analysis, transient expression of NSs, host infectivity assays, and population-level analyses of NSs and NSm. A Bushland isolate, designated HTPepRB, systemically infected two Tsw -containing pepper genotypes, whereas the Uvalde isolate did not. HTPepRB remained unable to overcome Sw-5b -mediated resistance in tomato. Consistent with the whole-virus phenotype, transient expression of HTPepRB NSs failed to elicit a detectable Tsw -dependent hypersensitive response, whereas NSs proteins from the Uvalde and College Station isolates retained avirulence activity. Across field-derived sequences from the three locations, NSs exhibited greater amino acid variation and location-associated sequence differentiation than NSm, with several Bushland-enriched substitutions and substitutions also present in previously reported resistance-breaking isolates. Because only HTPepRB was functionally linked to Tsw resistance breaking, these substitutions are considered candidates rather than causal determinants. HTPepRB links loss of detectable Tsw -dependent NSs recognition with a whole-virus resistance-breaking phenotype while remaining restricted by Sw-5b -mediated resistance. The greater sequence variation observed in NSs than NSm further identifies divergent NSs sequence backgrounds for future functional dissection of Tsw –NSs recognition.
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Kumar et al. (2026) studied this question.
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