Breeding Tm-1-based tomato rootstocks, resistant to tomato brown rugose fruit virus, to impede soil-mediated viral infections

Introduction – The Tobamovirus fructirugosum, tomato brown rugose fruit virus (ToBRFV) is a mechanically transmitted, seed- and soil-borne virus causing severe damage to tomato crops worldwide. Under monoculture conditions, infected residues enable ToBRFV to persist in soil, initiating infectious foci in newly planted seedlings. These plants are then exposed to foliar mechanical inoculations, facilitating disease spread. Management strategies include the use of ToBRFV-resistant germplasms. Methods – We screened 52 wild and 45 cultivated tomato varieties for ToBRFV resistance using foliar inoculation, symptom scoring, and ELISA. Lines harboring the Tm-1 resistance gene were used to generate resistant rootstocks and scions, which were challenged with ToBRFV. Grafting combinations of resistant and susceptible plants were evaluated under controlled root and foliar inoculations, as well as in commercial field trials. Results – Screening identified complete resistance in wild Solanum accessions and cultivated lines carrying Tm-1. Controlled experiments showed that susceptible rootstocks enabled infection of resistant scions following root inoculations, whereas resistant rootstocks limited soil-mediated infection of susceptible scions. In field trials, resistant rootstocks reduced early fruit symptoms. Combining resistant scions with resistant rootstocks (RS/RR) resulted in a 16.43% infection rate, compared to over 92% in susceptible controls. Discussion – Resistant rootstocks act as a barrier against soil-mediated ToBRFV transmission and reduce economic losses by limiting fruit symptoms. However, they do not protect against direct foliar infection. Thus, combining Tm-1-based resistant scions with resistant rootstocks is essential for durable disease management.