Begomoviruses can be found in association with alphasatellites, which are capable of autonomous replication but are dependent on the helper begomovirus for systemic infection, encapsidation and vector transmission. Previous studies suggest that the presence of NW alphasatellites (genus Clecrusatellite) is associated with more severe symptoms. To better understand this interaction, we investigated the effects of two alphasatellites on infectivity, symptom development, viral DNA accumulation and vector transmission of three begomoviruses in three hosts. In tomato and Nicotiana benthamiana, all combinations were infectious. In Leonurus sibiricus, only the ToYSV/ToYSA combination was infectious. The presence of EuYMA increased symptom severity of EuYMV and ToYSV in N. benthamiana, and the presence of ToYSA was associated with more severe symptoms of ToYSV in N. benthamiana and L. sibiricus. EuYMA increased the accumulation of ToYSV in N. benthamiana but reduced the accumulation of EuYMV in tomato and of ToSRV in N. benthamiana. The presence of ToYSA decreased the accumulation of ToYSV in N. benthamiana and L. sibiricus. ToYSA negatively affected transmission of ToSRV by Bemisia tabaci MEAM1. Together, our results indicate that NW alphasatellites can interact with different begomoviruses, increasing symptom severity and interfering in the transmission of the helper begomovirus. Understanding this interaction is important as it may affect the emergence of diseases caused by begomovirus–alphasatellite complexes in the field.

In a systematic field survey for plant-infecting viruses, leaf tissues were collected from trees showing virus-like symptoms in Brazil. After viral enrichment, total RNA was extracted and sequenced using the MiSeq platform (Illumina). Two nearly full-length picorna-like genomes of 9534 and 8158 nucleotides were found associated with Hovenia dulcis (Rhamnaceae family). Based upon their genomic information, specific primers were synthetized and used in RT-PCR assays to identify plants hosting the viral sequences. The larger contig was tentatively named as Hovenia dulcis-associated virus 1 (HDaV1), and it exhibited low nucleotide and amino acid identities with Picornavirales species. The smaller contig was related to insect-associated members of the Dicistroviridae family but exhibited a distinct genome organization with three non-overlapping open reading frames (ORFs), and it was tentatively named as Hovenia dulcis-associated virus 2 (HDaV2). Phylogenetic analysis using the amino acid sequence of RNA-dependent RNA polymerase (RdRp) revealed that HDaV1 and HDaV2 clustered in distinct groups, and both viruses were tentatively assigned as new members of the order Picornavirales. HDaV2 was assigned as a novel species in the Dicistroviridae family. The 5′ ends of both viruses are incomplete. In addition, a nucleotide composition analysis (NCA) revealed that HDaV1 and HDaV2 have similarities with invertebrate-infecting viruses, suggesting that the primary host(s) of these novel virus species remains to be discovered.

Tomato (Solanum lycopersicum) ranks as the most important crop among greenhouse-planted crops in terms of cultivated areas (17,800 ha) and production in Argentina. In September 2014, farmers reported that tomato plants of cv. Elpida (Enza Zaden) showed mosaic and blistering on leaves in La Plata (Buenos Aires green-belt). The diseased plants occurred together in the same line, showing a typical pattern of mechanically transmitted pathogens. Although incidence did not exceed 1.5%, it was distributed in several distant locations within the district, posting a serious threat to the tomato production. Five samples were collected from symptomatic plants and tested for tospovirus, begomovirus and Cucumber mosaic virus by reverse transcription polymerase chain reaction (RT-PCR) (Dewey et al., 1996), PCR (Rojas et al., 1993) and enzyme-linked immunosorbent assay (ELISA), respectively. All results were negative. The samples were then examined under transmission electron microscopy. Isometric virus-like particles o...

Mixed infection between two or more begomoviruses is commonly found in tomato fields and can affect disease outcomes by increasing symptom severity and viral accumulation compared with single infection. Viruses that affect tomato include tomato severe rugose virus (ToSRV) and tomato rugose mosaic virus (ToRMV). Previous work showed that in mixed infection, ToRMV negatively affects the infectivity and accumulation of ToSRV. ToSRV and ToRMV share a high degree of sequence identity, including cis-elements in the common region (CR) and their specific recognition sites (iteron-related domain, IRD) within the Rep gene. Here, we investigated if divergent sites in the CR and IRD are involved in the interaction between these two begomoviruses. ToSRV clones were constructed containing the same nucleotides as ToRMV in the CR (ToSRV-A_(ToR:CR)), IRD (ToSRV-A_(ToR:IRD)) and in both regions (ToSRV-A_(ToR:CR+IRD)). When plants were co-inoculated with ToRMV and ToSRV-A_(ToR:IRD), the infectivity and accumulation of ToSRV were negatively affected. In mixed inoculation of ToRMV with ToSRV-A_(ToR:CR), high infectivity of both viruses and high DNA accumulation of ToSRV-A_(ToR:CR) were observed. A decrease in viral accumulation was observed in plants inoculated with ToSRV-A_(ToR:CR+IRD). These results indicate that differences in the CR, but not the IRD, are responsible for the negative interference of ToRMV on ToSRV.