Strongylodon macrobotrys: new host of soybean mosaic virus in Brazil.

Abstract

Strongylodon macrobotrys, commonly known as the jade vine, emerald vine, or turquoise jade vine, is a species of Fabaceae native to the Philippines. The plants have blue-green color inflorescences, which makinge them one of the most admired ornamental plants in Brazil (Muniz et al. 2015). In addition, the plants contain compounds with anticancer properties (Ragasa et al. (2014) isolated compounds from S. macrobotrys with anticancer properties. In March 2019, an adult jade plant, grown under the trellis system in an experimental area at the campus of the University of São Paulo (USP), Piracicaba, state of São Paulo, was found showing mosaic symptoms typical of a virus infection. Preliminary examination of negatively stained leaf extracts by transmission electron microscopy detected elongated, flexuous particles similar tolike thoseat of a potyviruses. Further observations of thin sections of symptomatic leaf tissues revealed the presence of cylindrical inclusions, as well as bundles of thin, elongated, and filamentous particles, typical of potyvirus infection in epidermal, parenchymalparenchymal, and vascular regions, as well as bundles of thin, elongated and filamentous particles. Subsequent molecular and biological assays confirmed the presence of a potyvirusTo identify the species of the virus, .Presence of a potyvirus was confirmed by subsequent molecular and biological assays. Ttotal RNA was extracted from a pool of symptomatic leaves from the plant using the Purelink viral RNA/DNA kit (Thermo Fisher Scientific), and analyzed by one- step RT-PCR using potyviruses universal primers PV1/SP6 and WCIEN-sense (Mackenzie et al. 1998; Maciel et al. 2011), which amplify a 750-bp fragment. Total RNA extracted from an asymptomatic jade vine, obtained from a florist shop, was used as a negative controlincluded in the assay. PCR products at the expected size (~750-bp) were observed in the symptomatic plant but not in the asymptomatic plant. BLASTn analysis of the Nnucleotide sequence of the amplicon obtained only from total RNA of the symptomatic plant (GenBank accession no. MN970030) showed that it shares 90.82% to 97.859% identity with corresponding nucleotide sequences of the Korean isolate WS162 of soybean mosaic virus (SMV) deposited at the GenBank (, accession no. FJ640973, FJ640956, D88616). Extracts from symptomatic leaves of the jade plant wereas mechanically inoculated onto leaves of healthy plants of jade vine, Jack bean (Canavalia ensiformis), soybean cv. NA 5909 (Glycine max), cowpea (Vigna unguiculata), and passion fruit (Passiflora edulis f. flavicarpa). One plant of jade plant and four plants of each other species were inoculated , and infection was assessed based and monitored for symptom expression on symptom expression, and RT-PCR. The jade vine and Jack bean plants were infected by SMV, showingdeveloped mild mosaic symptoms approximately 60 and 15 days after inoculation, respectively , whereas the plants of other species were absent of any visible symptoms . To confirm the potyvirus identity, the jade vine samples were also tested by cConventional RT-PCR with SMV-specific primers pairs CP-F-SMV/CP-R-SMV (Jaramillo Mesa et al., 2018) and SMV-CPf/SMV-CPr (Wang and Ghabrial, 2002), thawhicht amplify fragments of 1000 990-bp and 469-bp90, respectively, nucleotides offrom the CP geneome region of SMV was performed, respectively. Amplicons of expected sizes were obtained from the total RNA of the leaves of field-infected and the mechanically inoculated plant of jade plantsvine as well as the Jack bean plants, but not from the asymptomatic jade plantvine and plants of other species the negative control. The viral nucleotide sequences obtained with the above pairs of primersBLASTn analysis of nucleotide sequences of the amplicons showed that they share 96.81% and 97.63% identity, respectively, with the same Korean SMV isolate WS162. These results demonstrate that… the field-symptomatic jade vine was infected with SMV, which is naturally transmitted by aphids speciess in a non-persistent manner and via soybean infected seeds (Hajimorad et al. 2018)( ). The virus appears to have has a restricted narrow natural host range., Aapart from soybean, and to date, it has only been reported the natural infection has been documented only in soybean, Lagenaria siceraria, Passiflora spp., Pinellia ternata, Senna occidentalis, and Vigna angularis (Almeida et al., 2002; Chakraborty et al. 2016; Hajimorad et al. 2018). To our knowledge, this is the first report of SMV in S. macrobotrys in the world. Further surveys are necessary to determine the incidence of the virus in ornamental jade plants vines and its importance as virus reservoirs for commercial soybean crops.