Infection of groundnut ringspot virus in Plumeria pudica characterized by irregular virus distribution and intermittent expression of symptoms

Plumeria pudica, known as bridal bouquet, exhibiting characteristic symptoms of orthotospovirus infection were found in different localities in Brazil. Symptoms were restricted to leaves of the middle and lower thirds of a few branches of each plant. Electron microscopy, molecular analyses, and complete genome sequencing identified the orthotospovirus as groundnut ringspot virus (GRSV),member of the species Orthotospovirus arachianuli. The virus was poorly transmitted mechanically to P. pudica. Reverse transcription polymerase chain reaction (RT-PCR) and reverse transcription quantitative polymerase chain reaction (RT-qPCR) analyses performed using total RNA extracted from leaf blades, primary veins, petioles, and regions of petiole insertion on branches indicated the presence of GRSV, predominantly in the symptomatic leaf blades. Symptomatic branches propagate vegetatively, often resulting in plants expressing GRSV symptoms. In contrast, vegetative propagation of the asymptomatic branches of infected plants predominantly generates plants without GRSV symptoms. The resistance of P. pudica plants to GRSV infection, restricted systemic viral movement, and expression of symptoms in infected plants suggest that this orthotospovirus does not threaten this ornamental plant.

Characterization of Soybean, Tomato, and Nicandra physalodes as Sources of Inoculum of Tomato Severe Rugose Virus to Tomato Crops

Tomato severe rugose virus (ToSRV) is one of Brazil's main begomoviruses infecting tomato (Solanum lycopersicum). Recent studies indicate that soybean (Glycine max) crops harboring the whitefly Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) may have epidemiological significance by acting as an asymptomatic amplifier host for the virus. In this study, we gathered experimental greenhouse and field evidence of the role of soybean in the epidemiology of the disease caused by ToSRV. Tomato and Nicandra physalodes, known as good sources of inoculum of this begomovirus, were used as references. The infection rates of soybean, tomato, and N. physalodes with ToSRV in greenhouse no-choice transmission tests with B. tabaci MEAM1 were 50, 71.4, and 64.2%, respectively. The transmission efficiencies of ToSRV to tomato when B. tabaci MEAM1 acquired the virus in ToSRV-infected soybean, tomato, and N. physalodes were 43, 33, and 20%, respectively. Leaves of ToSRV-infected soybean, tomato, and N. physalodes used as sources of inoculum had similar virus titers. In the host preference assay, viruliferous whiteflies preferred to land on tomato rather than soybean and N. physalodes, whereas aviruliferous whiteflies landed indistinctly on these plants. Under experimental field conditions, the transmission efficiency of ToSRV to tomato was higher when tomato was used as a source of inoculum, followed by N. physalodes and soybean. Considering that soybean is extensively cultivated in several Brazilian states that also grow tomato, it can serve as an efficient asymptomatic source of inoculum and support the recent hypothesis that it can also play, under certain conditions, a relevant role as an amplifier host in the epidemiology of the disease caused by ToSRV.

First report of groundnut ringspot virus infecting Zinnia sp. in Brazil

Zinnia sp. is a genus belonging to Asteraceae family, originated in Mexico and adapted to a warm-hot climate (Hemmati and Mehrnoosh, 2017). Several types of zinnias with different flower color and forms are cultivated in Brazil (Min et al., 2020 and Souza Jr. et al., 2020). Characteristic symptoms of infection caused by orthotospovirus, including chlorotic spots and concentric rings on the leaves, were observed in two plants of Zinnia sp. of a florist located in the city of Piracicaba, State of São Paulo, Brazil. Orthotospovirus-like particles were observed by transmission electron microscope in leaf extracts from both plants, stained negatively with 1% uranyl acetate. By analyzing ultrathin sections of infected leaf tissues, particles of 80-100 nm in diameter were found in the lumen of the endoplasmic reticulum and nucleocapsid aggregates in the cytoplasm. Total RNA extracted separately from the leaves of both samples, using the Purelink Viral DNA / RNA kit (Thermo Fisher Scientific), was used to detect the virus by reverse transcription polymerase chain reaction (RT-PCR), using the universal primers for orthotospovirus BR60, complementary to the 3' end of the non-translated region of the S RNA (position 1 to 15 nt), and BR65, matching the nucleocapsid gene (N) (position 433 to 453 nt), generating and amplicon of 453 nt (Eiras et al., 2001). Amplicons of the expected size were obtained for the two samples. An amplicon was purified with the Wizard SV Gel and PCR Clean-Up System kit (Promega) and sequenced in both directions at Macrogen Inc (South Korea). The nucleotide sequence (GenBank MW629018) showed 99.29-99.76% identity with nucleotide sequences of the orthotospovirus groundnut ringspot virus (GRSV) isolates (GenBank MH686229 and KY400110). Leaf extracts from symptomatic plants were also analyzed by plate-trapped antigen-enzyme-linked immunosorbent assay (PTA-ELISA), using polyclonal antiserum produced against the GRSV nucleocapsid protein (Esquivel et al., 2019). The absorbance values obtained for the extracts of the two symptomatic plants of Zinnia sp. (1.3 and 1.7) were twice as high as the value obtained for the healthy plant extract (0.5). Leaf extract of symptomatic Zinnia sp. was inoculated mechanically onto leaves of healthy plants of Zinnia sp., Capsicum annuum cv. Dara, Cucumis sativus, Cucurbita pepo cv. Caserta, Chenopodium amaranticolor, Datura stramonium, Nicotiana tabacum cv. Turkish and Solanum lycopersicum cv. Compack. At 5 days post inoculation (dpi), inoculated leaves of D. stramonium reacted with local lesions, and at 9 dpi, newly developed leaves of inoculated S. lycopersicum plants showed necrotic spot and concentric ring symptoms, whereas C. annuum exhibited concentric rings at 10 dpi. Inoculated zinnia plants showed systemic chlorotic spot and concentric ring symptoms at 20 dpi, indistinguishable from those observed under natural infection. The other inoculated plant species were not symptomatic, nor the virus was detected. PTA-ELISA and RT-PCR confirmed infection with GRSV in symptomatic plants. The amplicons generated by RT-PCR of total RNA extracted from an experimentally infected plant of C. annuum and D. stramonium, and two plants of Zinnia sp. were sent for nucleotide sequencing. The obtained nucleotide sequences (MW629019, MW629020, MW629021, MW629022) shares 100% identity with the nucleotide sequence corresponding to the original GRSV isolate (MW629018) identified in Zinnia sp. This is the first report of the natural occurrence of GRSV in Zinnia sp. in Brazil. Studies on incidence and damage are needed to recommend alternatives for management.

First report of costus stripe mosaic virus infecting Tradescantia spathacea plants in Brazil

Tradescantia spathacea (family Commelinaceae) is cultivated worldwide as an ornamental (Golczyk et al., 2013) and as medicinal plant (Tan et al., 2020). In 2019, 90 of ~180 plants of T. spathacea, grown in two beds of 4 m2 and exhibiting leaf mosaic were found in an experimental area at ESALQ/USP (Piracicaba municipality, São Paulo state, Brazil). Potyvirus-like flexuous filamentous particles were observed by transmission electron microscopy in foliar extracts of two symptomatic plants stained with 1% uranyl acetate. Total RNA was extracted using the Purelink viral RNA/DNA kit (Thermo Fisher Scientific) from leaves of two symptomatic plants and separately subjected to a reverse transcription polymerase chain reaction (RT-PCR). The potyviruses degenerate pairs of primers CIFor/CIRev (Ha et al. 2008), which amplifies a fragment corresponding to part of the cylindrical inclusion protein gene, and WCIEN/PV1 (Maciel et al. 2011), which amplifies a fragment containing part of the capsid protein gene and the 3' untranslated region, were used. The expected amplicons (~700bp) were obtained from both total RNA extracts. Two amplicons from one sample were purified using the Wizard SV Gel and PCR Clean-Up System kit (Promega) and directly sequenced in both directions at Macrogen Inc (Seoul, South Korea). The obtained nucleotide sequences (GenBank MW430005 and MW503934) shared 95.32% and 97.79% nucleotide identity, respectively, with the corresponding sequences of the Brazilian isolate of the potyvirus costus stripe mosaic virus (CoSMV, MK286375) (Alexandre et al. 2020). Extract from an infected plant of T. spathacea was mechanically inoculated in 10 healthy plants of T. spathacea and two plants each of the following species: Capsicum annuum, Chenopodium amaranticolor, Commelina benghalensis, Datura stramonium, Gomphrena globosa, Nicandra physaloides, Nicotiana tabacum cvs. Turkish and Samsun, Solanum lycopersicum, T. palida, and T. zebrina. All T. spathacea plants exhibited mosaic and severe leaf malformation. C. benghalensis plants developed mild mosaic, whereas infected T. zebrina plants were asymptomatic. The plants of other species were not infected. RT-PCR with specific CoSMV primers CoSMVHC-F and CoSMVHC-R (Alexandre et al. 2020) confirmed the infection. Nucleotide sequences of amplicons obtained from experimentally inoculated T. spathacea and T. zebrina (MW430007 and MW430008) shared 94.56% and 94.94% identity with the corresponding sequence of a Brazilian CoSMV isolate (MK286375). None of eight virus-free plants of T. spathacea inoculated with CoSMV using Aphis craccivora exhibited symptoms, nor was CoSMV detected by RT-PCR. Lack of CoSMV transmission by A. solanella, Myzus persicae, and Uroleucon sonchi was previously reported (Alexandre et al. 2020). T. spathacea plants are commonly propagated vegetatively, and by seeds. Virus-free seeds, if available, can provide an efficient and easy way to obtain healthy plants. Only three viruses were reported in plants of the genus Tradescantia: Commelina mosaic virus, tradescantia mild mosaic virus, and a not fully characterized potyvirus (Baker and Zettler, 1988; Ciuffo et al., 2006; Kitajima 2020). CoSMV was recently reported infecting Costus spiralis and C. comosus (Alexandre et al. 2020). As far as we know, this is the first report of CoSMV infecting T. spathacea plants.

First report of bidens mosaic virus infecting Centella asiatica in Brazil

Centella asiatica is a perennial, herbaceous creeper plant that belongs to the family Apiaceae. It has been known since prehistoric times and has been used for therapeutic and cosmetic purposes (James and Dubery 2009; Gohil et al. 2010), and is easily propagated vegetatively. In 2018, plants of C. asiatica exhibiting foliar symptoms of mosaic and malformation were found in the botanical garden of the Plantarum Institute (Nova Odessa municipality, São Paulo state - 22°46'45.8"S 47°18'47.5"W) and in an experimental area at ESALQ/USP (Piracicaba municipality, São Paulo state - 22°42'26.0"S 47°37'48.6"W). In both locations the plants were grown in beds of approximately 4 m2 and all of them were symptomatic. Initially, leaf extract from symptomatic C. asiatica plants was examined by transmission electron microscopy (TEM) after being negatively stained with 1% uranyl acetate. Potyvirus-like flexuous filamentous particles were observed in leaf samples from both locations. TEM of thin sections of symptomatic leaf tissues revealed the presence of cylindrical inclusions, characteristic of infection by potyviruses, in the cytoplasm of epidermal, parenchymal, and vascular cells. Total RNA was extracted from symptomatic leaves collected in the Plantarum Institute (3 samples), and at Escola Superior de Agricultura Luiz de Queiroz (1 sample) using the Purelink viral RNA/DNA kit (Thermo Fisher Scientific, Waltham, USA). Reverse Transcription -Polymerase Chain Reaction (RT-PCR) was performed using the degenerate primers CIFor (5'-GGIVVIGTIGGIWSIGGIAARTCIAC-3') and CIRev (5'-ACICCRTTYTCDATDATRTTIGTIGC-3'), which amplify a fragment of approximately 700 bp within the the cylindrical inclusion protein gene of potyviruses (Ha et al. 2008). Amplicons of the expected size were obtained for all four samples analysed. One amplicon per location was purified using the Wizard® SV Gel and PCR Clean-Up System kit (Promega), and directly sequenced in both directions at Macrogen Inc (Seoul, South Korea). The nucleotide sequences obtained from the symptomatic C. asiatica plants collected in the Plantarum Institute (GenBank Acc. No. MT668627), and at ESALQ/USP (GenBank Acc. No. MT668626) showed 97.1% and 96.2% identity, respectively, with the nucleotide sequence of a Brazilian isolate of bidens mosaic virus (BiMV), family Potyviridae, genus Potyvirus (GenBank Acc. No. KF649336). To confirm the infection of C. asiatica plants with BiMV, the previously extracted RNAs were analyzed by RT-PCR using the specific primers 8331 (5'-CGTGGGGCTATCCTGAATTG-3') and 9046 (5'-CCACATCAGAGAAGTGTGCC-3'), which amplify a fragment of 715 bp corresponding to the BiMV coat protein gene (Suzuki et al. 2009). The expected size amplicons were obtained for all four samples of symptomatic plants of C. asiatica. The nucleotide sequences of two amplicons (GenBank Acc. Nos. MT668628, and MT668629), representing plants from each location, showed 94.6% to 95.6% identities with corresponding nucleotide sequences of the coat protein gene of BiMV from Brazil (GenBank Acc. Nos. KF649336, AY960150, and AY960151). A leaf extract of a symptomatic C. asiatica plant was mechanically inoculated to healthy plants of Apium graveolens, Bidens pilosa, C. asiatica, Chenopodium amaranticolor, C. quinoa, Coriander sativum, Nicotiana benthamiana, N. tabacum and Petroselinum crispum. C. asiatica became systemically infected, reproducing the original symptoms of leaf mosaic and malformation. N. benthamiana was infected and developed severe mosaic symptoms, whereas C. amaranticolor and C. quinoa reacted only with necrotic and chlorotic local lesions, respectively. Other assayed plants were not infected. Potyvirus-like particles were observed by TEM in the infected plants and BiMV infection was confirmed by RT-PCR. Transmission assays of the BiMV isolate by aphids Myzus persicae and Aphys gossypii to healthy C. asiatica plants were also performed. Virus-free aphids of the two species, reared on Capsicum annuum and Gossypium hirsutum respectively, were fasted for 30 min and then placed, separately, on symptomatic leaves of C. asiatica for an acquisition access period (AAP) of 10 min. After that, groups of six insects were transferred, separately, to four healthy C. asiatica plants for an inoculation access period (IAP) of 24 h. After inoculation the insects were killed manually. Approximately 30 days later, one plant inoculated with each species of aphid exhibited symptoms and infection was confirmed by RT-PCR and nucleotide sequencing of the amplicons. BiMV was absent in control, non-inoculated plants in both mechacial and aphid transmission assays. Infection of spontaneously growing C. asiatica plants by potyvirus, determined by TEM, was previously reported in Curitiba and Colombo, state of Paraná, Brazil by Lima Neto and Souza (1981), but the virus was not fully characterized and identified. In addition to BiMV, plants of C. asiatica are also suscptible to infection with cucumber mosaic virus (CMV), as reported by Cardin and Moury (2010) in Madagascar. This is the first identification of BiMV naturally infecting C. asiatica. Additional works on effects of BiMV infection of C. asiatica on commercial production and pharmaceutical properties are required.

Kinetics of Systemic Invasion and Latent and Incubation Periods of Tomato severe rugose virus and Tomato chlorosis virus in Single and Co-Infections in Tomato Plants

Tomato severe rugose virus (ToSRV) and Tomato chlorosis virus (ToCV) are among the major viruses that affect tomato (Solanum lycopersicum) development and yield in Brazil. ToSRV and ToCV are transmitted in a persistent circulative and semipersistent manner, respectively, by the whitefly Bemisia tabaci Middle East-Asia Minor 1, considered the main vector of these viruses. In this study, the kinetics of systemic invasion and the latent and incubation periods of ToSRV and ToCV were evaluated in singly and doubly infected tomato plants. Both viruses moved systemically into tomato plants as early as 1 day after inoculation. The mean ToCV latent periods in single infections and co-infections with ToSRV were 13 and 11 days, respectively, while incubation periods in single and co-infections were, on average, 30 and 31 days, respectively. For ToSRV, the mean latent period was 7 days in single infections and 6 days in co-infections with ToCV. Incubation periods were, on average, 18 and 17 days in single and co-infections, respectively. Because latent periods for both viruses were shorter than their respective incubation periods, field-infected tomato plants may act as sources of inocula soon after infection and before onset of symptoms.