RESISTANCE BREAKING TOMATO SPOTTED WILT VIRUS ISOLATES ON RESISTANT TOMATO CULTIVARS IN ITALY

A. Crescenzi, A. Fanigliulo , A. Viggiano
In summer 2012, typical symptoms of Tomato spotted wilt disease occurred on tomato plants of different resistant cultivars (carrying the Sw5 gene), in different fields in Foggia province (Apulia region, southern Italy). The percentage of symptomatic plants was 20-30% and, in particular cases of advanced stage of cultivation, it reached up to 50% at the end of cycle. All TSWV isolates induced similar, very serious, systemic symptoms of bronzing in all resistant, infected tomato hybrids. Leaf extracts from these samples were tested by ELISA for the detection of TSWV, CMV, TMV, ToMV, INSV, PVY, AMV, PepMV, PVX, TYLCV, TYLCSV, PZSV and by molecular hybridization for the detection of PSTVd and CLVd. TSWV was detected in all the tested samples. The correspondent virus isolate was inoculated mechanically and by Frankliniella occidentalis on to a set of different tomato hybrids, in order to investigate for its ability to overcome the resistance gene Sw5, beyond that on some herbaceous test plants. The TSWV isolate, after three single lesion passages in Nicotiana glutinosa, induced symptoms typical of TSWV in mechanically inoculated seedlings grown from the same seed lots as the field-grown tomato plants. The virus isolate, designated TSWV-RB-TI, inoculated to plants of five commercial tomato hybrids carrying the Sw5 gene (that had previously shown resistance to different TSWV isolates), and five pepper hybrids carrying the Tsw gene, was later detected by ELISA in most inoculated tomato plants of each hybrid: systemic infection occurred a few days before local lesions appeared in inoculated leaves as a consequence of the typical hypersensitivity reaction caused by the Sw5 gene. By contrast, pepper hybrids carrying the Tsw gene were uninfected by TSWV-RB-TI isolate. The RB isolate did not differ noticeably in transmission efficiency when it was tested with the thrips F. occidentalis.
This is not the first report of a TSWV strain infecting tomato plants carrying the Sw5 gene. Our observations demonstrate that new evolved strains of TSWV have emerged in southern Italy in 2012, able to overcome the Sw5 resistance gene in tomato hybrids previously known to be resistant to the virus.
Crescenzi, A., Fanigliulo , A. and Viggiano, A. (2015). RESISTANCE BREAKING TOMATO SPOTTED WILT VIRUS ISOLATES ON RESISTANT TOMATO CULTIVARS IN ITALY. Acta Hortic. 1069, 95-98
DOI: 10.17660/ActaHortic.2015.1069.13
https://doi.org/10.17660/ActaHortic.2015.1069.13
Tomato spotted wilt virus, TSWV, Sw5 gene, Resistance breaking (RB), tomato
English

Acta Horticulturae