Eggplant mild leaf mottle virus (EMLMV), a new putative member of the genus Ipomovirus that harbors an HC-Pro gene.

Since 2003, a new viral disease of eggplant (Solanum melongena L.) has been spreading in fields in the Jordan and Arava Valleys, Israel. The symptoms of this disease include mild leaf mottling and varying degrees of fruit distortion. This disease can be transmitted by mechanical sap inoculation, as well as by the whitefly Bemisia tabaci (Homoptera, Aleyrodidae) and has been tentatively named eggplant mild leaf mottle virus (EMLMV). Our study aimed to determine the complete sequence and genome organization of EMLMV. The extracted viral RNA was subjected to SOLiD next-generation sequence analysis and used as a template for reverse transcription synthesis, which was followed by ds-cDNA synthesis or PCR amplification. The ssRNA genome of EMLMV includes 9,280 nucleotides, excluding a 3' terminal poly-adenylated tail. The genome includes a putative single, large open reading frame (ORF) that encodes a polyprotein of 3,011 amino acids, a short overlapping ORF of PIPO protein comprised of 71 amino acids and 5' and 3' non-coding regions of 108 and 136 nucleotides, respectively. The deduced amino acid sequence of the EMLMV polyprotein is relatively close to that of sweet potato mild mottle virus (SPMMV), with 37% shared sequence identity. Among the four ipomoviruses, only SPMMV and the putative genus member EMLMV contain a helper component-proteinase (HC-Pro) gene. Like SPMMV-HC-Pro, EMLMV-HC-Pro also contains the highly conserved PTK domain that is thought to be involved in the aphid-assisted transmission of potyviruses.

Spread of Tomato apical stunt viroid (TASVd) in Greenhouse Tomato Crops Is Associated with Seed Transmission and Bumble Bee Activity.

Tomato apical stunt viroid (TASVd) has been reported as a devastating pathogen of greenhouse tomato in Israel. This isolate shares 92 and 99% identity with the Ivory Coast type strain and an Indonesian strain, respectively. No information is available regarding the epidemiology of this viroid complex. The present study indicates that TASVd is not transmitted by the aphid Myzus persicae or the whitefly Bemisia tabaci, nor through root infection in infested soil. However, the results indicate that the viroid may be able to invade the embryonic tissues of the seed and transmission rates through seed may reach 80%. Moreover, it was confirmed that bumble bees (Bombus terrastris) can transmit the viroid from infected tomato source plants to healthy plants. Based on these findings, it is suggested that the primary spread of the viroid in greenhouse tomato plants is by seed transmission, and secondary distribution occurs by the pollination activity of bumble bees.

UV radiation effects on pathogens and insect pests of greenhouse-grown crops.

Production of high-value crops is often performed under protected cultivation. In recent years various spectral modifications have been made in greenhouse covers. Two of the main reasons to modify the spectral characteristics of greenhouse covers have been to suppress the proliferation of several foliar diseases and to protect crops from insects and insect-borne virus diseases of greenhouse-grown crops. These goals were achieved by complete or partial absorption of solar UV radiation, which interrupts the life cycle of several fungal pathogens and alters the visual behavior of many insects. Examples of these management strategies are described in this article.

Management of air-borne viruses by "optical barriers" in protected agriculture and open-field crops.

The incurable nature of viral diseases and the public awareness to the harmful effects of chemical pest control to the environment and human health led to the rise of the integrated pest management (IPM) concept. Cultural control methods serve today as a central pivot in the implementation of IPM. This group of methods is based on the understanding of the complex interactions between disease agents and their vectors as well as the interactions between the vectors and their habitat. This chapter describes a set of cultural control methods that are based on solar light manipulation in a way that interferes with vision behavior of insects, resulting in a significant crop protection against insect pests and their vectored viruses.

Ipomovirus--an atypical genus in the family Potyviridae transmitted by whiteflies.

Ipomoviruses (genus Ipomovirus) are whitefly-transmitted viruses assigned to the family Potyviridae. They are characterised by filamentous flexible particles and a positive-sense single-stranded RNA (+ssRNA) genome. The viral genome is translated into a polyprotein precursor, which is processed into mature proteins and a short overlapping open reading frame. The genus Ipomovirus contains four accepted species and one unapproved species, and two other tentative members have recently been characterised. Ipomoviruses cause serious economic losses in many important crops, including cassava, sweet potato, cucurbits, tomato and aubergine. These viruses are transmitted by whiteflies in a non-circulative, semi-persistent manner, the virions being retained on the external surface of the vectors' mouthparts for a few days or weeks. Comparison of the available complete genome sequences of different ipomoviruses revealed differences in their genome organisation and a considerable variation in their proteins and conserved motifs that may reflect functional differences. This review summarises the current knowledge of the members within the genus Ipomovirus, focusing on genome organisation, taxonomic classification and the mechanism by which they are transmitted.

The complete genomic sequence of pepper yellow leaf curl virus (PYLCV) and its implications for our understanding of evolution dynamics in the genus polerovirus.

We determined the complete sequence and organization of the genome of a putative member of the genus Polerovirus tentatively named Pepper yellow leaf curl virus (PYLCV). PYLCV has a wider host range than Tobacco vein-distorting virus (TVDV) and has a close serological relationship with Cucurbit aphid-borne yellows virus (CABYV) (both poleroviruses). The extracted viral RNA was subjected to SOLiD next-generation sequence analysis and used as a template for reverse transcription synthesis, which was followed by PCR amplification. The ssRNA genome of PYLCV includes 6,028 nucleotides encoding six open reading frames (ORFs), which is typical of the genus Polerovirus. Comparisons of the deduced amino acid sequences of the PYLCV ORFs 2-4 and ORF5, indicate that there are high levels of similarity between these sequences to ORFs 2-4 of TVDV (84-93%) and to ORF5 of CABYV (87%). Both PYLCV and Pepper vein yellowing virus (PeVYV) contain sequences that point to a common ancestral polerovirus. The recombination breakpoint which is located at CABYV ORF3, which encodes the viral coat protein (CP), may explain the CABYV-like sequences found in the genomes of the pepper infecting viruses PYLCV and PeVYV. Two additional regions unique to PYLCV (PY1 and PY2) were identified between nucleotides 4,962 and 5,061 (ORF 5) and between positions 5,866 and 6,028 in the 3' NCR. Sequence analysis of the pepper-infecting PeVYV revealed three unique regions (Pe1-Pe3) with no similarity to other members of the genus Polerovirus. Genomic analyses of PYLCV and PeVYV suggest that the speciation of these viruses occurred through putative recombination event(s) between poleroviruses co-infecting a common host(s), resulting in the emergence of PYLCV, a novel pathogen with a wider host range.

Control methods of virus diseases in the Mediterranean basin.

Viral pathogens form an important group of obligatory parasites of plants. About 977 plant viruses have been described and classified in 14 families and 70 genera. This group of pathogens has complex interactions with their host plants and vectors due to their integration in the molecular mechanisms of living cells, interfering with our ability to manage the malfunctions of virus infected plants by curing means. These constraints led to the perception that the best protection from virus diseases is by prevention. Many cultural procedures used for virus control are aimed at eradicating or altering one or more of the primary participants in the transmission process (vector, virus source plants, and the crop) or preventing their coming together. Part of these control measures were devised to reduce to a minimum, the number of inoculative vector individuals that are active in the crop or interfere with the transmission process at any of its phases, thereby arresting virus spread. Advances in plant virology and a better understanding of plant vector interactions provide strategies based on the formation of mechanical and optical barriers that interfere with the ability of the viral pathogen or its vector to reach the plant and initiate an epidemic.

Transgenic cucumbers harboring the 54-kDa putative gene of Cucumber fruit mottle mosaic tobamovirus are highly resistant to viral infection and protect non-transgenic scions from soil infection.

Cucumber fruit mottle mosaic tobamovirus (CFMMV) causes severe mosaic symptoms and yellow mottling on leaves and fruits and, occasionally, severe wilting of cucumber (Cucumis sativus L.) plants. No genetic source of resistance against this virus has been identified in cucumber. The gene coding for the putative 54-kDa replicase gene of CFMMV was cloned into an Agrobacterium tumefaciens binary vector, and transformation was performed on cotyledon explants of a parthenocarpic cucumber cultivar. R1 seedlings were screened for resistance to CFMMV by symptom expression, back inoculation on an alternative host and ELISA. From a total of 14 replicase-containing R1 lines, eight resistant lines were identified. Line 144--homozygous for the putative 54-kDa replicase gene--was immune to CFMMV infection by mechanical and graft inoculation, and to root infection following planting in CFMMV-infested soil. A substantial delay of symptom appearance was observed following infection by three additional cucurbit-infecting tobamoviruses. When used as a rootstock, line I44 protected susceptible cucumber scions from soil infection by CFMMV. This paper is the first report on protection of a susceptible cultivar against a soil-borne viral pathogen, by grafting onto a transgenic rootstock.