First report of a resistance-breaking isolate of Tomato spotted wilt virus infecting sweet pepper harboring the Tsw gene in Argentina

FERRAND, LUCIANA, MARIA LAURA GARCIA; RESENDE RENATO; BALATTI PEDRO, ELENA DAL BÓ

PLANT DISEASE

AMER PHYTOPATHOLOGICAL SOC

Año: 2015

0191-2917

The disease caused by Tomato spotted wilt virus (TSWV) is endemic on vegetablecrops in Buenos Aires green belt, the most important vegetable production area inArgentina (18,000 ha). Approximately, half of the greenhouse surface planted withsweet pepper (Capsicum annuum L.) in the country is located in La Plata (BuenosAires). In this area, TSWV had limited sweet pepper production until theintroduction of resistant genotypes harboring the Tsw resistance gene thatreplaced 100% of the susceptible cultivars. However, in November 2013, resistantpeppers showing typical Tospovirus symptoms were observed in La Plata.Symptoms appeared 20 days after transplanting in early spring and by midsummer100% of the plants were affected in many greenhouses, causing importanteconomic losses in this season. Samples from symptomatic plants were analyzedby ELISA with antisera against the viruses: TSWV, Groundnut ringspot virus(GRSV), Tomato chlorotic spot virus (TCSV), Potato virus Y (PVY), Cucumbermosaic virus (CMV) and Tobacco mosaic virus (TMV). All samples were positiveonly for TSWV. Presence of TSWV was confirmed by RT-PCR with primersdesigned from a conserved sequence of the N gene that amplified a fragment ofabout 450 bp. Further, RFLP using BstNI and HinCII enzymes that cut the 450 bpfragment specifically (Dewey et al; 1996), showed the typical restriction pattern ofTSWV. To test the ability to overcome the resistance, this greenhouse-isolate,named TSWV-A2, was mechanically transmitted to two commercial peppercultivars carrying the Tsw gene, cv. Almuden and cv. Platero (10 plants each).After two weeks, all plants were systemically infected showing the typicalsymptoms of TSWV infection. RT-PCR (as previously described) from total RNAextracted from symptomatic leaves of these plants, confirmed the presence ofTSWV-A2. Therefore, we demonstrated that TSWV-A2 is able to overcome Tswgene resistance. Furthermore, to amplify the complete N gene of TSWV-A2 isolate,a new RT-PCR was carried out (Lovato et al. 2008). A specific 800 bp product wascloned and sequenced (GenBank accession No KP719131). Blast analysis showedthat the sequence was 99% homologous at the nucleotide as well as the aminoacid sequence to the N gene of isolates EF195230 and EF195224 from SouthKorea (Kim et al. 2004). In addition, TSWV-A2 showed to share commoncharacteristics with the resistant-breaking isolates infecting sweet pepper cultivarscarrying the Tsw gene, previously reported in Italy (Roggero et al. 2002) and Spain(Margaria et al. 2004). Overall, based on biological, serological and molecularfeatures, this is the first report of a local isolate of TSWV breaking the Tswresistancein sweet pepper in Argentina.