Elvira Fiallo-Olivé

Emerging Virus Diseases Transmitted by Whiteflies

Virus diseases that have emerged in the past two decades limit the production of important vegetable crops in tropical, subtropical, and temperate regions worldwide, and many of the causal viruses are transmitted by whiteflies (order Hemiptera, family Aleyrodidae). Most of these whitefly-transmitted viruses are begomoviruses (family Geminiviridae), although whiteflies are also vectors of criniviruses, ipomoviruses, torradoviruses, and some carlaviruses. Factors driving the emergence and establishment of whitefly-transmitted diseases include genetic changes in the virus through mutation and recombination, changes in the vector populations coupled with polyphagy of the main vector, Bemisia tabaci, and long distance traffic of plant material or vector insects due to trade of vegetables and ornamental plants. The role of humans in increasing the emergence of virus diseases is obvious, and the effect that climate change may have in the future is unclear.

Tomato leaf deformation virus, a novel begomovirus associated with a severe disease of tomato in Peru

Begomovirus infection was suspected in tomato plants exhibiting symptoms of curling and deformation of leaves observed in a survey conducted in northern and central Peru. Rolling circle amplification and restriction fragment length polymorphism analyses suggested that a begomovirus was present in symptomatic plants. The full-length sequence of a begomovirus DNA component was determined, comprising 2591 nucleotides. Based on its genome organization, we suggest it corresponds to the DNA-A of a New World begomovirus. Less than 89% nucleotide sequence identity to known begomoviruses was found, indicating that it corresponds to an isolate of a distinct begomovirus species for which the name tomato leaf deformation virus (ToLDeV) is proposed. Different stretches of the genomic component have the highest sequence identity with different viruses compatible with a recombinant origin. Sequence segments shared common ancestors with isolates of either soybean blistering mosaic virus, tomato yellow spot virus, or tomato chino La Paz virus. Partial sequence analysis of begomovirus isolates present in symptomatic tomato samples collected in northern and central Peru suggested widespread occurrence of this new begomovirus. This is the first confirmation of a begomovirus infection in tomatoes in Peru.

Begomoviruses infecting weeds in Cuba: increased host range and a novel virus infecting Sida rhombifolia.

As a result of surveys conducted during the last few years to search for wild reservoirs of begomoviruses in Cuba, we detected a novel bipartite begomovirus, sida yellow mottle virus (SiYMoV), infecting Sida rhombifolia plants. The complete genome sequence was obtained, showing that DNA-A was 2622 nucleotides (nt) in length and that it was most closely related (87.6% nucleotide identity) to DNA-A of an isolate of sida golden mosaic virus (SiGMV) that infects snap beans (Phaseolus vulgaris) in Florida. The DNA-B sequence was 2600 nt in length and shared the highest nucleotide identity (75.1%) with corchorus yellow spot virus (CoYSV). Phylogenetic relationship analysis showed that both DNA components of SiYMoV were grouped in the Abutilon clade, along with begomoviruses from Florida and the Caribbean islands. We also present here the complete nucleotide sequence of a novel strain of sida yellow vein virus found infecting Malvastrum coromandelianum and an isolate of euphorbia mosaic virus that was found for the first time infecting Euphorbia heterophylla in Cuba.

Deciphering the biology of deltasatellites from the New World: maintenance by New World begomoviruses and whitefly transmission

Deltasatellites are small noncoding DNA satellites associated with begomoviruses. The study presented here has investigated the biology of two deltasatellites found in wild malvaceous plants in the New World (NW). Infectious clones of two NW deltasatellites (from Malvastrum coromandelianum and Sidastrum micranthum) and associated begomoviruses were constructed. Infectivity in Nicotiana benthamiana and their natural malvaceous hosts was assessed. The NW deltasatellites were not able to spread autonomously in planta, whereas they were maintained by the associated bipartite begomovirus. Furthermore, NW deltasatellites were transreplicated by a monopartite NW begomovirus, tomato leaf deformation virus. However, they were not maintained by begomoviruses from the Old World (tomato yellow leaf curl virus, tomato yellow leaf curl Sardinia virus and African cassava mosaic virus) or a curtovirus (beet curly top virus). NW deltasatellites did not affect the symptoms induced by the helper viruses but in some cases reduced their accumulation. Moreover, one NW deltasatellite was shown to be transmitted by the whitefly Bemisia tabaci, the vector of its helper begomoviruses. These results confirm that these molecules are true satellites. The availability of infectious clones and the observation that NW deltasatellites reduced virus accumulation paves the way for further studies of the effect on their helper begomoviruses.

Complete genome sequences of two begomoviruses infecting weeds in Venezuela

The complete sequences of isolates of two new bipartite begomoviruses (genus Begomovirus, family Geminiviridae) found infecting weeds in Venezuela are provided. The names proposed for these new begomoviruses are “Datura leaf distortion virus” (DLDV), isolated from a Datura stramonium L. (family Solanaceae) plant, and “Dalechampia chlorotic mosaic virus” (DCMV), isolated from infected Dalechampia sp. (family Euphorbiaceae) and Boerhavia diffusa L. (family Nyctaginaceae) plants. Phylogenetic analysis showed that these new begomoviruses segregated in two distinct clades of New World begomoviruses. To our knowledge, this is the first record of a begomovirus infecting Dalechampia sp. plants. Also, this is the first report of a begomovirus infecting Boerhavia spp. and Datura spp. in Venezuela.

Complete genome sequences of two novel begomoviruses infecting common bean in Venezuela

The complete genome sequences of isolates of two new bipartite begomoviruses (genus Begomovirus, family Geminiviridae) found infecting common bean in Venezuela are provided. The names proposed for each of these viruses are “bean yellow chlorosis virus” (BYCV) and “bean white chlorosis mosaic virus” (BWCMV). Phylogenetic analysis showed that they segregated in two distinct clades of New World begomoviruses. This is the first report of begomoviruses infecting common bean in Venezuela.

Stylet penetration activities of the whitefly Bemisia tabaci associated with inoculation of the crinivirus Tomato chlorosis virus

Bemisiatabaci is an important vector of numerous plant viruses, including the emergent semi-persistently transmitted crinivirus Tomato chlorosis virus (ToCV). Its vector feeding behaviour is complex, with important implications for virus transmission, epidemiology and control. Thus, the objective of this study was to investigate the role of the stylet penetration activities of B. tabaci in the inoculation of ToCV in tomatoes by using the electrical penetration graph (EPG) technique. EPG recordings were classified into six categories depending on the waveforms observed. The results showed that ToCV inoculation is mainly associated with stylet activities in phloem sieve elements (E1 waveform), as there was a significant increase in the rate of transmission when whiteflies performed waveform E1. The precise stylet activities - either salivation or egestion - associated with virion release, presumably from retention sites in the foregut, need further investigation.

Cotton leaf curl Gezira alphasatellite associated with tomato leaf curl Sudan virus approaches the expected upper size limit in the evolution of alphasatellites

Begomoviruses (family Geminiviridae) cause severe damage to tomato crops worldwide. Among them, tomato leaf curl disease (ToLCD)-associated begomoviruses are a major concern for tomato production in Sudan. Here, we report the detection of unexpectedly large cotton leaf curl Gezira alphasatellite molecules (up to 1467 nt) associated with an isolate of a novel strain of tomato leaf curl Sudan virus (ToLCSDV) in tomato plants affected by ToLCD. A recombinant nature is suggested for this ToLCSDV isolate.

Desmodium mottle virus, the first legumovirus (genus Begomovirus) from East Africa

A novel bipartite legumovirus (genus Begomovirus, family Geminiviridae), that naturally infects the wild leguminous plant Desmodium sp. in Uganda, was molecularly characterized and named Desmodium mottle virus. The highest nucleotide identities for DNA-A, obtained from two field-collected samples, were 79.9% and 80.1% with the legumovirus, soybean mild mottle virus. DNA-B had the highest nucleotide identities (65.4% and 66.4%) with a typical non-legumovirus Old World begomovirus, African cassava mosaic virus. This is the first report of a legumovirus in East Africa and extends the known diversity of begomoviruses found infecting wild plants in this continent.

Complete genome sequence of jacquemontia yellow vein virus, a novel begomovirus infecting Jacquemontia tamnifolia in Venezuela

Wild plants of the family Convolvulaceae are hosts for a few New World begomoviruses (genus Begomovirus, family Geminiviridae). In this work, we report the complete genome sequence of a new begomovirus infecting the wild convolvulaceous plant Jacquemontia tamnifolia in Venezuela. The cloned bipartite genome showed the organization of typical New World begomoviruses and was found to be phylogenetically related to those of begomoviruses from Venezuela and other Caribbean countries. Several recombination events have been shown to have occurred involving genome fragment exchange with related begomoviruses infecting crops such as tomato and cucurbits and wild plants, including Jacquemontia sp. We propose the name jacquemontia yellow vein virus (JacYVV) for this new begomovirus.