Evaluation of responses to tomato brown rugose fruit virus (ToBRFV) and selection of resistant lines in Solanum habrochaites and Solanum peruvianum germplasm

Reactions of plants in 173 wild tomato accessions belonging to Solanum habrochaites and S. peruvianum were studied by inoculation with a tobamovirus, tomato brown rugose fruit virus (ToBRFV). Around 10-50% of plants in nine accessions of S. habrochaites and one of S. peruvianum were demonstrated to be highly resistant. Resistant plants showed no symptoms at 22-24 degrees C, and no virus could be detected in their inoculated and newly developed leaves using bioassays and RT-qPCR. ToBRFV-resistant plants were also resistant to tobacco mosaic virus and tomato mosaic virus. The susceptible wild tomatoes were infected systemically with ToBRFV showing different severity of symptoms. When resistant plants inoculated with ToBRFV were incubated in a plant growth chamber at a temperature of 33 degrees C, they expressed mosaic and deformation symptoms, indicating that the resistance was broken at elevated temperature. However, when these plants were transferred to the greenhouse at 24 degrees C, their newly emerged leaves showed no symptoms, and the virus could not be detected in the new leaves. Cleft grafting was done with scions from a resistant plant of S. habrochaites LA1739 into ToBRFV-infected susceptible tomato rootstock. The scions became infected and showed mosaic symptoms indicating that the resistance was ineffective after grafting. Sequences comparison of Solyc08g075630 loci of nine resistant accessions showed high heterogenity. Only one resistant plant of S. habrochaites carried an allele almost identical to the resistance gene reported previously. All other resistant plants may have probably unknown gene(s) of resistance to ToBRFV.