Genome Sequence Resource of a Tm -2 2 Resistance-Breaking Isolate of Tobamovirus tomatotessellati (Tomato Mosaic Virus) Infecting Solanum pimpinellifolium in the United States

Tomato mosaic virus (ToMV, Tobamovirus tomatotessellati ), is an economically important tobamovirus of tomato that has been effectively controlled through the deployment of the Tm -2 2 resistance gene. However, resistance-breaking (RB) strains have emerged. In 2023, Solanum pimpinellifolium plants exhibiting mosaic and mottling symptoms were observed in a seed-increase plot at the University of California, Davis. A tobamovirus was detected with an ImmunoStrip test in the symptomatic leaves. Sequence analysis of a RdRp fragment amplified by RT-PCR and a general tobamovirus primer pair revealed 99.8% identity with a ToMV Tm -2 2 RB isolate (RB-ToMV-KMT) previously reported from Japan. Following biological purification, the ToMV isolate (RB-ToMV-CA-23) from S. pimpinellifolium was mechanically inoculated onto tomato genotypes carrying Tm -2 2 (LA2828 and LA2939). Most LA2828 plants developed severe mosaic, stunting, leaf deformation, and systemic necrosis; whereas only a small proportion of LA2939 plants developed mild mosaic symptoms. The movement protein (MP) amino acid mutation D240Y, previously associated with most Tm -2 2 RB ToMV isolates, was identified in the MP of RB-ToMV-CA-23. High-throughput sequencing was used to determine the complete 6,384-nt genome sequence of the RB-ToMV-CA-23 isolate, which is 99.8% identical to that of RB-ToMV-KMT. This is the first report of a Tm -2 2 RB ToMV isolate in the U.S.A., and demonstrates how the virus can be introduced into new areas.