Abstract
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 °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 °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 °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.
Highlights
Resistance and tolerance to different viruses have been found in several wild tomato species, especially Solanum pimpinellifolium, S. peruvianum and S. habrochaites (Razdan and Mattoo 2006)
The great majority of 173 accessions of S. habrochaites and S. peruvianum proved to be susceptible to ToBFRV-Tom2Jo of which all individual plants expressed systemic symptoms with disease severity indices (DSI) ranging 20–100% (Table S1)
No symptoms were detected in the cuttings that originated from rooted shoots of the symptomless plants after inoculation with tobacco mosaic virus (TMV) and tomato mosaic virus (ToMV) after 40 dpi
Summary
Wild tomatoes serve as excellent model systems for both basic and applied plant research. Because of their genetic diversity, they have been utilized as the source of resistance to pathogens (Kole 2011). With the aim of control them, three dominant resistance genes marked Tm-1, Tm-2 and Tm-22 have been introgressed from wild tomatoes to the cultivated S. lycopersicum. The Tm-1 gene, mapped on chromosome 2, is incompletely dominant originated from S. habrochaites PI 126,445 and suppresses virus replication (Fraser et al 1980; Holmes 1954; Pelham 1972). The alleles Tm-2 and Tm-22 discovered in S. peruvianum PI 126,926 and PI 128,650 respectively are located on chromosome 9 and confer complete dominant resistance by restricting the virus movement (Alexander 1963; Laterrot and Pecaut 1969; Schroeder et al 1967).
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