HR-Mediated Defense Response is Overcome at High Temperatures in Capsicum Species

Resistance to Tomato spotted wilt virus isolated from paprika (TSWV-Pap) was overcome at high temperatures ($30{\pm}2^{\circ}C$) in both accessions of Capsicum annuum S3669 (Hana Seed Company) and C. chinense PI15225 (AVRDC Vegetable Genetic Resources). S3669 and PI15225, which carrying the Tsw gene, were mechanically inoculated with TSWV-Pap, and then maintained in growth chambers at temperatures ranging from $15{\pm}2^{\circ}C$ to $30{\pm}2^{\circ}C$ (in $5^{\circ}C$ increments). Seven days post inoculation (dpi), a hypersensitivity reaction (HR) was induced in inoculated leaves of PI152225 and S3669 plants maintained at $25{\pm}2^{\circ}C$. Meanwhile, necrotic spots were formed in upper leaves of 33% of PI15225 plants maintained at $30{\pm}2^{\circ}C$, while systemic mottle symptoms developed in 50% of S3669 plants inoculated. By 15 dpi, 25% of S3669 plants had recovered from systemic mottling induced at $30{\pm}2^{\circ}C$. These results demonstrated that resistance to TSWV-Pap can be overcome at higher temperatures in both C. chinense and C. annuum. This is the first study reporting the determination of temperatures at which TSWV resistance is overcome in a C. annuum genetic resource expressing the Tsw gene. Our results indicated that TSWV resistance shown from pepper plants possess the Tsw gene could be overcome at high temperature. Thus, breeders should conduct evaluation of TSWV resistance in pepper cultivars at higher temperature than $30^{\circ}C$ (constant temperature).