First Report of Tomato severe rugose virus, a Tomato-Infecting Begomovirus, in Soybean Plants in Brazil.

Begomoviruses cause economically important diseases on tomato (Solanum lycopersicum) in Brazil, and are transmitted by whiteflies (Bemisia tabaci). Tomato severe rugose virus (ToSRV) is currently the predominant tomato-infecting begomovirus in Brazil. Reservoirs of ToSRV are tomatoes, Nicandra physaloides, and common beans (Barbosa et al. 2009; Macedo et al. 2017). In Brazil, tomato and soybean cultivations are frequently associated, and soybeans often serve as a major source of whiteflies for tomato. However, it is not known if ToSRV infects soybeans. Therefore, 301 symptomless plants were randomly sampled from 16 soybean fields near tomato fields in six municipalities of Brazil in the states of Goiás, Minas Gerais, and São Paulo from 2013 to 2016. PCR was performed on total DNA extracts with ToSRV-specific primers (ToSRV1f-ToSRV2r; Fernandes et al. 2010). Ten samples were positive (820-bp amplicons). Rolling circle amplification (RCA) and RFLP analysis (Msp I) were performed with these 10 ToSRV-positive samples, and the patterns of digestion were identical to each other and to that of an isolate of ToSRV (ToSRV-1164, Macedo et al. 2015). Direct sequencing of the RCA products of the 10 ToSRV-positive soybean samples with the PAR1c496 primer (Rojas et al. 1993), which generates the sequence of part of the coat protein gene and the intergenic region, revealed 98 to 99% identity with the corresponding ToSRV sequence (accession KX458238). The full-length DNA-A component of one of the ToSRV isolates from soybean (S1014) was cloned, sequenced (KX828624), and was 99% identical to the sequence of a ToSRV isolate from bean (KX458238). Direct sequencing of the RCA product from S1014 with the degenerate DNA-B primer PBL1v2040 (Rojas et al. 1993) generated a partial BC1 (MP) sequence that was 97% identical to that of ToSRV (EF534708). To confirm the susceptibility of soybeans to ToSRV, soybean plants cv. Davis were inoculated by biolistics with the RCA preparation from S1014. By 21 days post-inoculation (dpi), no obvious symptoms were observed, but ToSRV was detected in all plants by PCR (12/12, results of two experiments). Tomato plants bombarded with the S1014 RCA extract developed typical symptoms of ToSRV (mosaic and mottling), whereas tomato and soybean plants bombarded with RCA extracts from healthy plants showed no symptoms and were negative for ToSRV by PCR. In addition, whitefly transmission was performed using B. tabaci MEAM-1 (biotype B). Soybean plants cv. Davis infected with ToSRV (S1014) by particle bombardment were exposed to adult whiteflies for a 48-h acquisition access period. These whiteflies were then provided a 48-h inoculation access period on soybean and tomato plants (∼50 adults per plant). At 21 dpi, inoculated soybean plants had not developed symptoms, but 6/10 plants were infected with ToSRV based on PCR detection, whereas 10/14 tomato plants developed typical symptoms and were positive for ToSRV by PCR (two independent experiments). All soybean and tomato plants exposed to nonviruliferous whiteflies showed no symptoms and were negative for ToSRV by PCR. These results indicate that ToSRV induces a symptomless infection in soybean, and that such plants could serve as a reservoir of ToSRV for the tomato crop in Brazil. © 2017, American Phytopathological Society. All rights reserved.