A severe symptom phenotype in pepper cultivars carrying the Tsw resistance gene is caused by a mixed infection between resistance-breaking and nonresistance-breaking isolates of Tomato spotted wilt virus

Abstract

Pepper (Capsicum annuum) plants with the Tsw resistance gene showing unusually severe symptoms consisting of local lesions, chlorosis, stunting and systemic necrosis on the apical leaves were found in a commercial field in north eastern Spain in 2009. The presence of Tomato spotted wilt virus (TSWV) was confirmed in all diseased plants. After mechanical inoculation of Nicotiana glutinosa with infected field samples, biological clones of the virus were isolated from individual local lesions. These biological clones produced two different types of symptoms after inoculation on Tsw resistant pepper plants: (I) typical symptoms caused by resistance-breaking (RB) isolates characterized by chlorosis and stunting, and (II) severe symptoms as observed in the field plants. Similar symptoms in pepper plants carrying the Tsw resistance gene were reproduced under controlled conditions, after simultaneous inoculation of RB and non-resistance-breaking (NRB) isolates. The NRB isolate was detected in a low proportion in the apical uninoculated leaves, whereas NRB isolates could not infect resistant pepper when inoculated alone. Co-infection by NRB and RB isolates induced disease synergism with systemic necrosis on the apical leaves. To our knowledge, this is the first case in which a synergic interaction between isolates of the same virus has been described, which has the ability to overcome a natural genetic resistance. This finding could have epidemiological implications for the management of TSWV.