Abstract
The single dominant Tsw resistance gene from Capsicum chinense against the Tomato spotted wilt orthotospovirus (TSWV) is temperature sensitive, i.e. the resistance fails to function at or above 32 °C. This study describes a new class of temperature‐sensitive resistance‐breaking TSWV isolates that induce Tsw‐mediated resistance at T < 28 °C but at T ≥ 28 °C break this resistance. The NSs genes from these isolates were cloned and expressed to be analysed for RNA silencing suppressor (RSS) activity and the ability to induce a Tsw‐mediated hypersensitive response (HR) in C. chinense and Capsicum annuum (Tsw+). Unlike in viral infection, transient expression of some of the NSs proteins at standard temperatures (22 °C) did not induce Tsw‐mediated HR, although varying degrees of RSS activity were observed. Attempts to express and test the NSs proteins for functionality at an elevated temperature through agroinfiltration remained unsuccessful. The NSs proteins of some TSWV resistance‐breaking (RB) isolates were analysed and found to lack amino acid residues that were previously shown to be important for RNA silencing suppression and avirulence. This study describes a new class of resistance‐breaking TSWV isolates that may be of importance for breeders and growers and for which the underlying mechanism still remains unknown.
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