Insights into the role of ethylene perception in tomato resistance to vascular infection by Verticillium dahliae

A Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) system was employed to investigate the role of the tomato ethylene receptor ETR4. By comparing wilting symptoms of verticillium wilt in wild-type, ethylene-insensitive Never ripe (Nr) mutant tomato plants and ETR4-silenced plants, it was demonstrated that disease severity in the Nr and ETR4-silenced plants was statistically reduced compared to wild-type plants. Disease incidence and severity were reduced by 11 and 20%, respectively, in the Nr plants compared to the wild-type plants, at 33 days post-inoculation (d.p.i.). In the ETR4-silenced plants, disease incidence and severity were reduced by 14 and 15%, respectively, compared to the TRV-only-inoculated plants, at 37 d.p.i. Quantification of Verticillium dahliae by qPCR revealed that the reduction in symptom severity in the Nr plants was associated with significant reduction of growth of the pathogen in the vascular tissues of the Nr plants compared to that in the wild-type plants, suggesting that impaired perception of ethylene via the Never-ripe receptor results in increased disease resistance. Fungal reduction was evident at each sampling day in the Nr plants, ranging from 1·5 to 1·75 times less than that in the wild-type plants. Fungal quantification in the ETR4-silenced and TRV-only-inoculated plants showed similar levels of fungal biomass.