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Tomato leaf curl New Delhi virus (ToLCNDV; family Geminiviridae, genus Begomovirus) is an emerging virus in horticulture crops in Asia, and has recently been introduced in Spain, Tunisia and Italy. No betasatellite DNA was detected in infected tomato and zucchini squash samples from Spain, and agroinoculated viral DNA‐A and DNA‐B were sufficient to reproduce symptoms in plants of both crop species. Infected tomato and zucchini squash plants also served as inoculum sources for efficient transmission either mechanically or using Bemisia tabaci whiteflies. Cucumber, melon, watermelon, zucchini squash, tomato, eggplant and pepper, but not common bean, were readily infected using viruliferous whiteflies and expressed symptoms 8–15 days post‐inoculation. New full‐length sequences from zucchini squash and tomato indicated a high genetic homogeneity (>99% sequence identity) in the ToLCNDV populations in Spain, pointing to a single recent introduction event.

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Tomato leaf curl New Delhi virus (ToLCNDV) (family Geminiviridae, genus Begomovirus) has recently been introduced in western Mediterranean countries. Isolates in Spain constitute a new strain, denominated ToLCNDV-ES, that is causing losses in commercial zucchini and melon crops; however, it is also, although less often, detected in commercial tomato crops. We developed a tissue-print hybridization test to detect the two genomic components of the virus and a TaqMan quantitative polymerase chain reaction (qPCR) test to estimate the number of genome copies in plants. qPCR was approximately 104 to 106 times more sensitive than tissue-print hybridization to detect viral genomic DNA-A and DNA-B, respectively. It also detected the virus in more experimentally and naturally ToLCNDV-ES-infected zucchini squash and tomato plants. ToLCNDV-ES DNA-A titers were significantly lower in tomato than in zucchini plants, often falling below the detection limits in the hybridization test. In addition, the DNA-B accumulation was impaired in tomato when compared with zucchini. According to the data obtained in this study, the differences in viral titers of both plant species contribute to explain the dissimilarities in symptom expression, capability of detection, and transmission of the virus.

In September 2011, symptoms typically associated with Bean yellow disorder virus (BYDV) such as intervenal mottling and yellowing on middle and lower leaves combined with brittleness were observed in green bean (Phaseolus vulgaris L.) produced in commercial greenhouses from Granada and Almeria provinces, Spain. The affected plants were all observed in greenhouses infested with Bemisia tabaci. However, collected samples tested negative for BYDV using a specific RT-PCR test (4). Electrophoretic double stranded (ds) RNA analysis from symptomatic plants revealed the presence of a slightly diffused high molecular weight dsRNA band of ~8.5 kb, similar to that produced by the crinivirus Lettuce cholorosis virus (LCV) (3). The dsRNA was purified and used for cDNA synthesis and PCR by uneven PCR (1) using primers derived from LCV genome sequences (GenBank FJ380118 and FJ380119). Amplified DNA fragments were cloned in pGEM-T Easy vector (Promega, Madison, WI) and sequenced. Two different sequences were obtained and the nucleotide and amino acid sequences were analysed using BLAST. Both showed the highest identity with different regions of the LCV genome. The sequence of the first product had 92% nucleotide and 98% amino acid sequence identity with the polyprotein (Orf1a) homologue from RNA1 of LCV (KC602376). The sequence from the second product (KC602375) revealed the highest nucleotide and amino acid identity with the heat shock protein 70 homologue from LCV (90% and 99%, respectively). Based on these sequences, two sets of specific primers were designed (LCVSP 3-forward 5′-AGTGACACAAGTTGGAGCCGAC-3′, LCVSP 4-low 5′-CAGTGTTTGTTGGATATCTGGGG-3′) and (LCVSP 1-forward 5′-TGTTGGAAGGTGGTGAGGTC-3′, LCVSP 2-low 5′-CAGAGACGAGTCATACGTACC-3′) and each produced amplicons of the expected size (463 and 434 nt, respectively) when used in RT-PCR from the collected field samples. Subsequent field surveys from 2012 to 2013 in commercial bean greenhouses confirmed the presence of LCV that apparently had replaced BYDV. Groups of 15 to 20 adults of B. tabaci introduced in clip cages were fed for 24 h on 12 green bean plants infected with LCV and later transferred to six seedlings of bean and six of lettuce (Lactuca sativa L.). After 2 and 4 weeks, total RNA from the lettuce and bean plants was extracted using Plant RNA Reagent (Invitrogen) and subjected to RT-PCR analysis with the LCV-SP 1-2 and LCVSP 3-4 primer sets. All six plants of bean and none of lettuce showed positive for LCV-SP and a repeat experiment revealed identical results. We also seeded and produced lettuce plants within a bean greenhouse that was naturally infected with the virus and infested with B tabaci whiteflies. Under these conditions, we observed that whiteflies migrated freely from the infected bean plants to lettuce. After 4 and 6 weeks, lettuce plants neither produced symptoms nor tested positive for LCV by RT-PCR. This result confirms the existence of a new putative strain of LCV, Lettuce chlorosis virus-SP, unable to infect lettuce plants. To date, natural infections of LCV have not been reported outside California, where the virus failed to infect P. vulgaris (2). This is also the first report of LCV in Spain that infects members of the family Leguminosae. Green bean in southeast Spain was produced in ~9,000 ha of greenhouses until the introduction of BYDV a decade ago, causing considerable economic damage. The recent finding of LCV-SP has urged the local phytosanitary inspections to include this virus in lab tests and to emphasize disease management strategies based on whitefly control. References: (1) X. Chen and R. Wu. Gene 185:195, 1997. (2) J. Duffus et al. Eur. J. Plant Pathol. 102:591, 1996. (3) N. M. Salem et al. Virology 390:45, 2009. (4) E. Segundo et al. Plant Pathol. 53:517, 2004.

Lettuce chlorosis virus-SP (LCV-SP) (family Closteroviridae, genus Crinivirus), is a new strain of LCV which is able to infect green bean plants but not lettuce. In the present study, high-throughput and Sanger sequencing of RNA was used to obtain the LCV-SP full-length sequence. The LCV-SP genome comprises 8825 nt and 8672 nt long RNA1 and RNA2 respectively. RNA1 of LCV-SP contains four ORFs, the proteins encoded by the ORF1a and ORF1b are closely related to LCV RNA1 from California (FJ380118) whereas the 3´ end encodes proteins which share high amino acid sequence identity with RNA1 of Bean yellow disorder virus (BnYDV; EU191904). The genomic sequence of RNA2 consists of 8 ORFs, instead of 10 ORFs contained in LCV-California isolate. The distribution of vsiRNA (virus-derived small interfering RNA) along the LCV-SP genome suggested the presence of subgenomic RNAs corresponding with HSP70, P6.4 and P60. Results of the analysis using RDP4 and Simplot programs are the proof of the evidence that LCV-SP is the first recombinant of the family Closteroviridae by crossover recombination of intact ORFs, being the LCV RNA1 (FJ380118) and BnYDV RNA1 (EU191904) the origin of the new LCV strain. Genetic diversity values of virus isolates in the recombinant region obtained after sampling LCV-SP infected green bean between 2011 and 2017 might suggest that the recombinant virus event occurred in the area before this period. The presence of LCV-SP shows the role of recombination as a driving force of evolution within the genus Crinivirus, a globally distributed, emergent genus.

Andalusia, southern Spain, is a major horticultural production region within the Mediterranean, where over 10,000 ha are dedicated to the production of pepper (Capsicum annuum L.). Approximately two-thirds of the area dedicated to this crop is in a greenhouse and the remaining one-third is comprised of open field crops. Using pepper as a model, we identified and compared the major diseases caused by viruses in the different geographic regions and agronomic systems within the region. Pepper crops in plastic-covered greenhouses were predominantly associated with arthropod-transmitted virus diseases, such as TSWV. CMV was predominant in provinces located inland, and PMoV was found independent of the agrosystem, disease control methods, or geographic location.

The tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite, single-stranded begomovirus that was first identified in India in 1995 affecting solanaceous crops. A different strain, named ToLCNDV-ES, was introduced in Spain in 2012 and causes severe symptoms in zucchini crops. Virus transmission experiments with the whitefly Bemisia tabaci, were used to compare the transmission parameters in zucchini and tomato plants. The minimum acquisition access period and inoculation access period of ToLCNDV-ES transmission was similar in zucchini and tomato. However, the transmission efficiency was significantly higher in zucchini (96%) compared to tomato (2%). The maximum retention of the virus in the vector was 16 days. B. tabaci feeding on, or recently emerged from infected zucchini plants, accumulated more virus than those from infected tomato, as determined by real-time PCR. A total of 20% of B. tabaci that were recently emerged from infected zucchini, and none from infected tomato, were able to transmit the virus to virus-free zucchini. The results may explain the different incidences of ToLCNDV-ES in zucchini and tomato crops in Spain. But they are also relevant for ToLCNDV-ES management of crops and the role of the trade and transport of infected plant material, when small-sized immature stages of B. tabaci could be a source of infection.