**2. Resistance-breaking tobamoviruses**

Plant viruses belonging to the genus *Tobamovirus* (currently comprised of 37 species) are rod-shaped particles encapsulating a single-stranded RNA (+ssRNA) genome of ~6.4 kb. The genome encodes four ORFs. ORF1 and ORF2, separated by a leaky stop codon, encode the 126 and 183 kDa replicase protein complex (recently reviewed in [21]). ORF3 encodes the 30 kDa movement protein (MP), and ORF4 encodes the 17.5 kDa coat protein (CP). The tobamoviruses endanger cultivars in the world. For more than a century, tobacco and tomato plants that belong to the *Solanaceae* family are infected by TMV [1, 2] and ToMV [4]. Resistance to these viruses was introduced to tomato plants by introgression [22]. However, the durability of resistance genes is compromised by the pathogen selection pressure that gradually breaks the plant defense system. In tomato plants, the durability of *Tm-1*, *Tm-2*, and *Tm-22* [23] resistance genes has recently been jeopardized by the newly discovered tobamoviruses *Tomato mottle mosaic virus* (ToMMV), reported in Brazil [24], Mexico [25], and the USA [26], and the *Tm-22* resistance-breaking *Tomato brown rugose fruit virus* (ToBRFV) reported in Jordan [27] and Israel [28] (**Figure 2**). Within the *Solanaceae* family, pepper crops were also affected in the last decades by *Tobamovirus* species, mostly by PMMoV that overcame the resistance conferred by the *L1-3* genes [29–31] and rarely the *L4* gene in Japan [32] and Israel [33]. In cucurbits, the production of cucumber, melon, and watermelon has been endangered by the globalized spread of CGMMV. Since its discovery by Ainsworth in 1935 [6], no commercial cultivars fully resistant to CGMMV are available although temperature-sensitive strains with specific resistance were reported.

**Figure 2.** *Tomato brown rugose fruit virus* (ToBRFV)-infected tomato (*Solanum lycopersicum*) plants. (**a, d**) Brown rugose symptoms developed on fruits. (**b, c**) yellow spots on fruits. (**a, e–g**) Mosaic pattern developed on leaves and narrowing accompanied by mottling leaves. (**g**) Necrotic symptoms on pedicle, calyces, and petioles.
