Carrot yellows disease has been associated for many years with the Gram-positive, insect-vectored bacteria, ‘Candidatus Phytoplasma’ and Spiroplasma citri. However, reports in the last decade also link carrot yellows symptoms with a different, Gram-negative, insect-vectored bacterium, ‘Ca. Liberibacter solanacearum’. Our study shows that to date ‘Ca. L. solanacearum’ is tightly associated with carrot yellows symptoms across Israel. The genetic variant found in Israel is most similar to haplotype D, found around the Mediterranean Basin. We further show that the psyllid vector of ‘Ca. L. solanacearum’, Bactericera trigonica, is highly abundant in Israel and is an efficient vector for this pathogen. A survey conducted comparing conventional and organic carrot fields showed a marked reduction in psyllid numbers and disease incidence in the field practicing chemical control. Fluorescent in situ hybridization and scanning electron microscopy analyses further support the association of ‘Ca. L. solanacearum’ with disease symptoms and show that the pathogen is located in phloem sieve elements. Seed transmission experiments revealed that while approximately 30% of the tested carrot seed lots are positive for ‘Ca. L. solanacearum’, disease transmission was not observed. Possible scenarios that may have led to the change in association of the disease etiological agent with carrot yellows are discussed. [Formula: see text] Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

The economic importance of ornamentals has been increasing in many countries, and international demand has rapidly expanded. Cut flowers represent the largest segment of the industry followed by flowering pot plants, tree and nursery crops, flower bulbs, and other propagation material. The horticultural sector has seen much structural change both nationally and internationally over the last decades, but the implications for plant health have been neglected. We review the trends in ornamental production in the context of recent developments including the movement towards a global horticultural market, the rise of the horticultural industry of many developing countries, and the risk of plant virus diseases. Over the decade, there have been many changes in the ornamental production and marketing. This has resulted from the introduction of many innovations in production, handling, and transport. These changes have contributed to a marked increase in the international exchange of plant material. In all continents, there is a general trend towards fewer and larger horticultural growers, an increasing role of supermarkets and a concentration of the retail pathways. However, the increase in volume of new materials carries new risks of the introduction of both new viruses and new vectors, and of new, potentially more severe isolates of those viruses that have been known for many years. New production facilities are expanding in South America and in emerging centers of cut flower production in Africa. An important trend in the international flower market is the increased emphasis on novelties and high quality. Morphology and plant architecture have gained increasing importance in breeding programs of ornamental plants. Quality factors related to flower longevity, as well as tolerance and resistance against pest and diseases, including viroids and viral diseases are essential criteria in a competitive floriculture market. As competition in the world market increases, quality becomes a more important factor.

Plant virus diseases, like diseases caused by other pathogens, appear to be proliferating at ever-increasing rates. Over the past several years, there has been an increase in new and emerging plant virus diseases.Global over-population and activities that disrupt the natural ecological balances between pathogens and hosts demonstrate that, directly and indirectly, man continues to be instrumental in the spread and establishment of new diseases. In light of growing international concern for crop biosecurity, new, emerging and threatening plant viral diseases are receiving greater attention. Improved and coordinated viral disease surveillance systems, enhanced global response capacity, and education and training of a multidisciplinary workforce are needed to adequately address new and emerging viral diseases.We present an updated list of new viruses and viroids, detected within the last five years. The list includes both new virus and known viruses in new ornamental hosts.

During 2009 - 2011, symptoms of curling, yellow and purple discoloration of leaves, stunting of shoots, and formation of bunchy, fibrous secondary roots were observed in several ornamental crops, carrot, celery, and parsley fields located in several production areas of Israel. Incidence of disease was almost 20-80% in individual affected fields. Moreover, the observed symptoms resembled those caused by Spiroplasma citri in carrots affected by the carrot purple leaf disease, recently reported in United States and in Spain. Analyses revealed that high percentage of symptomatic plants tested positive for S. citri. Some of the plants were double infected by S. citri and a phytoplasma. Leafhopper species known to vector phytoplasmas and/or spiroplasmas, have been trapped in several locations in Israel. To our knowledge, this is the first report of S. citri associated with the 'yellow disease' syndrome in open-field crops in Israel.

In 2000, a severe outbreak of phytoplasma-caused disease in Limonium spp. flowers devastated the industry in Israel; insecticides were not able to knock down and kill leafhopper vectors before they could transmit the pathogen. Nonchoice laboratory studies were conducted to determine the effect of UV-absorbing plastics oil the movement of leafhoppers toward light; UV-absorbing plastic significantly reduced leafhopper movement. In choice trials conducted in Sunlight, significantly more leafhoppers moved into the cage covered With regular plastic as opposed to the cage covered with UV-absorbing plastic. Field studies were conducted to determine at what height leafhoppers enter 2.5-3-m high walk-in tunnels; the majority enter the tunnels low to the ground, up to 1 m. Finally, field Studies were conduced to compare leafhopper population levels in walk-in tunnels covered with UV-absorbing plastic or screening, and with ventilation holes it different heights above the ground. Elevated ventilation holes and UV-absorbing tunnel covering significantly reduced Orosius orientalis entrance into tunnels. Ramifications of these finding for leafhopper control are discussed.

Peanut mottle virus (PeMoV) was identified for the first time in Israel in peanut plants expressing mottle symptoms. Particle morphology, biological properties and serology suggested that this virus belongs to the genus Potyvirus . The characteristics of the Israeli (IL) PeMoV were compared with those of previously reported isolates. Using RT-PCR, a 1393-bp fragment consisting of the helper component — proteinase (HC-Pro) and a 988-bp product containing the coat protein (CP) were amplified, cloned and sequenced. Comparison of the HC-Pro sequences for PeMoV-IL and PeMoV-M (reported previously), showed 98% homology at the amino acid (aa) level. The aa sequence homology of the entire CP of isolate IL and six other PeMoV isolates ranged from 92% to 98%. A phylogenetic analysis carried out using the CP nucleotide sequence data indicated close similarity between PeMoV-IL and an Australian isolate and between two M isolates. The conserved KITC and CCC motifs in the HC-Pro were replaced by KVSC and ASC, respectively, in PeMoV-IL as in strain M. The DAG motif in the CP was replaced by DAA in the PeMoV isolates including IL. These results prompted the examination of aphid transmissibility of PeMoV-IL which were low and variable among experiments. These results differ from a previous report showing high aphid transmission of PeMoV.

The four o'clock flower (Mirabilis jalapa L.), a native of tropical South America, has been naturalized as an ornamental garden plant in many parts of the world, including Israel. Plants are multi-branched perennials that produce fragrant colorful flowers over the course of a few months. Plants with small yellow leaves and petite, distorted flowers, resembling phytoplasma-like symptoms, were observed in a home garden in the north of Israel. Using a nested polymerase chain reaction assay (PCR) with phytoplasma universal primers a product of 860 bp was obtained. Sequence analysis of the PCR product associated with infected M jalapa clustered within a major group of phytoplasmas - 16SrII, peanut witches' broom - and showed a 99% similarity with alfalfa witches' broom, a member of this group. To the best of our knowledge this is the first report of phytoplasma infection in the four o'clock flower.

Phytoplasma diseases have been identified in Israel in numerous species of various botanical families. The disease occurs in ornamentals, vegetables, field crops and fruit trees. In cut flowers, the disease was identified in Ranunculus spp., Celosia, Anemone and Limonium. In all these cases the disease was sporadic with no serious economical losses. In 2003, symptoms typical of a phytoplasma infection were observed in a large number of Gypsophila paniculata L. (i.e. baby's breath) plants grown in commercial fields in Israel. The symptoms include leaf yellowing, production of abundant long and narrow leaves, stunting, shoot proliferation, poor flower set and consequently reduce the yield of flowers by up to 80%. Examination of ultrathin sections of samples from diseased plants by electron microscopy revealed the presence of pleomorphic membrane-bound bodies in the phloem cells. Total nucleic acid was extracted from asymptomatic and symptomatic Gypsophila leaves. All leaf samples from twenty symptomatic plants consistently tested positive using a polymerase chain reaction assay (PCR) with phytoplasma universal primers (P1/P7) that amplify a 1.8-kb phytoplasma, rDNA product and followed by nested PCR with R16F2n/R16R2 primers yielding a product of 1.2 kb. No PCR products were evident when DNA extracted from healthy plants was used as a template. Sequence analysis of the PCR products obtained from numerous preparations, associated with infected Gypsophila, clustered within one ribosomal group of phytoplasmas (16SrII), peanut witches' broom. This is the first published record of these phytoplasmas in Gypsophila in Israel. The present paper reports the outbreak of phytoplasma in Gypsophila grown in commercial fields in Israel, survey of potential insect vector(s) of phytoplasma and possible control strategies using screen barriers.

Phytoplasma-caused diseases have been identified in Israel in numerous species of various botanical families, primarily from crop plants. Northern Israel has the most diversity of phytoplasma groups followed by the northern Negev desert and Arava valley, with the center of the country having the least. There are proportionally more infected flowers than orchards (including vineyards) or than vegetable crops. Of the 15 known 16S rDNA phytoplasma groups, seven are represented in Israel. It is very likely that at least one group was imported into Israel from another area of the world.

A virus identified as Passiflora latent virus (PLV) was isolated from passion fruit plants. Particle morphology, host range and serological properties suggested that this virus belongs to the genus Carlavirus. The complete genomic sequence of PLV was determined by sequencing overlapping cDNA fragments. The genome consisted of 8386 nt, excluding the poly (A) tail and contained six open reading frames, typical of carlaviruses. The overall similarities of the predicted amino acid sequence of PLV to those of other carlaviruses ranged from 25 to 73%. Phylogenetic analysis indicated that PLV was closely related to lily symptomless virus and blueberry scorch virus. This is the first report of the complete nucleotide sequence and genome structure of PLV.

A novel carmovirus infecting angelonia (Angelonia angustifolia) was recently described independently by researchers in the United States, Israel, and Germany (1,2,4). Angelonia flower break virus (AnFBV) and Angelonia flower mottle virus were proposed as appropriate names for this carmovirus. The virus, causing stunting, mild leaf mottle, flower mottling, and flower breaking symptoms has been detected in naturally infected angelonia in the United States, Israel, and Germany (2,4). Here we report the first detection of natural infection of verbena (in the United States and Israel) and phlox (in the United States) by using a recently developed double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA; Agdia, Elkhart, IN). Prior to this report, verbena was considered insusceptible to carmovirus infection (3) and phlox was known as an experimental host for AnFBV (2). A comparative serological study including 27 virus species, demonstrated that DAS-ELISA did not cross-react with any viruses that commonly infect ornamentals or are related to carmoviruses, showing that the polyclonal antibodies are specific to AnFBV. Antibody specificity was confirmed by the carmovirus group PCR test (Agdia). Furthermore, reverse transcription-polymerase chain reaction with AnFBV specific primers (2) produced the expected 1172-bp band from all ELISA-positive samples tested. Between November 2005 and March 2006, AnFBV was detected in 181 of 567 verbena, 26 of 143 phlox, and 193 of 267 angelonia samples submitted to Agdia Testing Services by commercial ornamental propagators for virus testing. Most samples were asymptomatic, although a few exhibited mild leaf mottle. It should be noted that the number of AnFBV-infected samples might not accurately reflect the actual number of commercially produced plants infected with AnFBV because most of the samples analyzed originated from virus elimination programs. The detection of natural AnFBV infection of verbena, phlox, and angelonia suggests that AnFBV may be more widespread in the ornamental industry than previously thought. References: (1) S. Adkins et al. Phytopathology (Abstr.) 95(suppl.):S2, 2005. (2) S. Adkins et al. Phytopathology 96:460, 2006. (3) G. P. Martelli and M. Russo. Online publication. ICTVdB-The Universal Virus Database. 00.074.0.02, 2004. (4) S. Winter et al. New Disease Reports. Vol 12. Brit. Soc. Plant Pathol. Online publication, 2005.

ABSTRACT A new carmovirus was isolated from Angelonia plants (Angelonia angustifolia), with flower break and mild foliar symptoms, grown in the United States and Israel. The virus, for which the name Angelonia flower break virus (AnFBV) is proposed, has isometric particles, approximately 30 nm in diameter. The experimental host range was limited to Nicotiana species, Schizanthus pinnatus, Myosotis sylvatica, Phlox drummondii, and Digitalis purpurea. Virions were isolated from systemically infected N. benthamiana leaves, and directly from naturally infected Angelonia leaves, using typical carmovirus protocols. Koch's postulates were completed by mechanical inoculation of uninfected Angelonia seedlings with purified virions. Isometric particles were observed in leaf dips and virion preparations from both Angelonia and N. benthamiana, and in thin sections of Angelonia flower tissue by electron microscopy. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis of dissociated purified virus preparations, a major protein component with a molecular mass of 38 kDa was observed. Virion preparations were used to produce virus-specific polyclonal antisera in both Israel and the United States. The antisera did not react with Pelargonium flower break virus (PFBV), Carnation mottle virus (CarMV), or Saguaro cactus virus (SgCV) by either enzyme-linked immunosorbent assay or immunoblotting. In reciprocal tests, antisera against PFBV, CarMV, and SgCV reacted only with the homologous viruses. The complete nucleotide sequence of a Florida isolate of AnFBV and the coat protein (CP) gene sequences of Israeli and Maryland isolates were determined. The genomic RNA is 3,964 nucleotides and contains four open reading frames arranged in a manner typical of carmoviruses. The AnFBV CP is most closely related to PFBV, whereas the AnFBV replicase is most closely related to PFBV, CarMV, and SgCV. Particle morphology, serological properties, genome organization, and phylogenetic analysis are all consistent with assignment of AnFBV to the genus Carmovirus.

Phytoplasma diseases have been identified in Israel in numerous species of various botanical families. The disease occurs in cultivated ornamentals, vegetables, field crops, fruit trees and in the wild crops. In cut flowers, the disease was identified in Anemone and Ranunculus, and Matthiola spp. In these cases the disease was sporadic with no serious economical losses. However, in carrots the disease is known to occur since 1995, causing losses of great economic significance.In the summer of 1998, the disease was identified in Celosia sp., causing general yellowing of leaves, stunting, witch-broom growth of axillary shoots and flower malformation (phyllody). In ultrathin sections of infected tissue, pleomorphic particles were observed in sieve elements of the diseased plants but not in healthy ones. Direct polymerase chain reaction (PCR) with universal primers resulted in amplified products of the expected size when symptomatic samples were used. No PCR products were obtained from the healthy control plants.In October 2000, the disease was identified in Limonium spp. in the Arava Valley. Symptoms included leaf yellowing, production of abundant long and narrow leaves, production of small and/or white flowers, excessive branching similar to 'Asparagus ferns', and occasionally production of leaf-like structures instead of flowers. Transmission electron microscopy and PCR confirmed the presence of phytoplasma in the symptomatic plants. In December 2000 work was started on monitoring potential vectors by use of yellow sticky traps and vacuum sampling. To date, four species known to vector phytoplasmas and/or spiroplasmas have been trapped: Orosius orientalis (Matsumura), Circulifer haematoceps (Mulsant et Rey), C. tenellus (Baker) and Exitanius capicola Stal. Austroagallia sinuata (Mulsant et Rey) and Psammotettix spp. have also been trapped. Field collected O. orientalis, which occurs in the largest numbers, C. haematoceps and C. tenellus have tested positive for phytoplasma by PCR analysis. Transmission studies with field-collected specimens have been initiated and initial results indicate that O. orientalis can vector phytoplasma to clean Limonium plants in the laboratory. Transmission studies are in progress with a clean colony of O. orientalis and other leafhopper species.In October 2003, phytoplasma-like symptoms were observed in Eustoma russelianum and Gypsophila.

Wheat with yellow head disease (YHD) (yellow heads and mosaic leaf symptoms) has been observed in Kansas since 1997. A pathogen was transmitted from the infected wheat to maize by vascular puncture inoculation and to Nicotiana benthamiana by rub inoculation. The original infected wheat and infected maize and N. benthamiana test plants all produced a unique 32- to 34-kDa protein when analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Time-of-flight mass spectrometry analysis of the unique 32- to 34-kDa protein showed that the amino acid sequence was most closely related to the nucleoprotein of Rice hoja blanca virus, indicating that the virus causing YHD symptoms in wheat is a tenuivirus. Antiserum made to this protein failed to react with extracts made from healthy wheat or wheat infected with Wheat streak mosaic virus or the High Plains virus. The antiserum did react to extracts made from symptomatic wheat, maize, and N. benthamiana, shown by SDS-PAGE to contain the unique protein, and to extracts of wheat with YHD symptoms from Kansas, North Dakota, South Dakota, and Oklahoma. The name Wheat yellow head virus is proposed for this virus.

The levels of polymorphism and the genetic relationships of eight populations of two thrips species, Thrips tabaci Lindeman and Frankliniella occidentalis (Pergande), were studied using amplified fragment length polymorphism. We used two combinations of restriction enzymes (EcoR I/Mse I and EcoR I/ Taq 1) and studied six of these eight populations with each combination. The two species could be distinguished morphologically and are clearly distinguished one from the other by either enzyme combination. We found a few unique bands characterizing some of the populations within each species and a high level of polymorphism within each population. The relatively low polymorphism between populations compared with those between species, suggests that gene transfer between populations does occur. The high level of polymorphism within populations suggests a high level of heterozygosity and a significant level of sexual reproduction for both species.

Ornithogalum mosaic virus (OrMV) causes flower deformation and deterioration of planting stocks in species and hybrids of Ornithogalum and Lachenalia. No resistance to viral infection by OrMV is known, making utilization of transformation technologies the natural choice for the introduction of virus resistance. Transformation with viral coat protein (CP) and replicase genes has been shown to confer resistance to viral infection in many plant species. Liquid-grown cell clusters of O. dubium were bombarded with gold particles coated with a plasmid carrying nptII gene, conferring kanamycin resistance, GUS reporter gene, and either CP gene or the viral replicase (N1b) target genes under the control of either polyubiquitin (UBQ3) or the strawberry vein-banding virus deleted (Delta SVB) promoters. Following prolonged selection in a liquid medium supplemented with 80 mg/1 kanamycin in darkness, the cultures were transferred to regeneration medium in the light, where hundreds of putative transgenic plantlets developed. Most of the regenerated plants were GUS-positive. PCR analysis indicated the presence of GUS reporter gene and nptII selectable gene, and either the CP or replicase transgenes. Transgenic plants are being propagated vegetatively before being challenged with virus infection to confirm their state of resistance.

Papaya (Carica papaya) plants grown in Israel were severely damaged by a disease named Nivun Haamir dieback (NHDB) (Franck & Bar-Joseph, 1992). Symptoms of NHDB resembled those of Australian papaya dieback (PpDB) associated with Candidatus Phytoplasma australiense (Liu et al., 1996; White et al., 1998). Field observations of NHDB suggested an airborne pathogen, but electron microscope studies failed to associate it with a phytoplasma (Franck & Bar-Joseph, 1992). Recently, 15 papaya plants suspected of having NHDB were tested for phytoplasma by nested PCR using P1/P7 and R16F2n/R16R2 primers. Phytoplasma products were confirmed by direct sequencing of the 16S/23S spacer region (SR), in which nine out of 15 samples with symptoms tested positive but all healthy controls were negative. Grapevines (Vitis vinifera) with symptoms of leaf rolling and red coloration, growing close to the papaya plots, were also tested and found positive. The SR sequences (851 bp) from papaya (GenBank accession no. AY903951) and grapevine were identical. When compared with other phytoplasmas, these sequences showed the highest similarity with phytoplasmas from the 16SrXII Stolbur group: Stolbur-Ph-Lily (AY169309), 97·66%; Sugarcane phytoplasma – Mauritius strain (AJ539181), 97·65%; grapevine yellows Germany (VK) (X76428), 97·54%; Australian grapevine yellows (AGY) (X95706) and Phormium yellow leaf (PYL) (U43569), 96·48%. This is the first report of the association between NHDB and a 'Ca. Phytoplasma australiense' isolate. The high degree of similarity between the NHDB-associated phytoplasma and that infecting grapes suggests a common inoculum source and probably a common vector. The use of papaya plants as indicators for gaining epidemiological information on the temporal spread of the phytoplasmas to vineyards is under investigation.

Genetic transformation mediated by bombardment with microscopic metal particles carrying target genes is the preferred method for the introduction of foreign genes into monocotyledonous plants. The fact that most flower bulbs are monocotyle-donous and that almost all commercial cultivars are propagated vegetatively makes them good candidates for molecular breeding through microprojectile bombard-ment. We report here on a development of a reliable method for an efficient genetic transformation of both Lilium longiflorum and Ornithogalum dubium using a particle inflow gun to deliver gene constructs into the target plant tissue, followed by a prolonged selection in the dark in liquid medium supplemented with kanamycin. The system was first optimized for Lilium longiflorum 'Snow Queen'. Based on the level of transient GUS expression, liquid-grown cell clumps are more competent than leaves. Large cell clusters (2-10 mm) maintain their organogenic potential while smaller clusters (<2 mm) cease to grow and die. The liquid-grown tissue cultures have a level of competence for transformation about 50-70 times greater than that of solid-grown callus cultures, and compact cell clusters are more competent than loose clusters. The cells were bombarded with a pCAMBIA2301 vector, carrying nptII gene conferring kanamycin resistance and GUS reporter gene. Following selection for 4-6 months in a liquid medium supplemented with 80 mg l(-1) kanamycin in the dark, the cell clusters were transferred to a regeneration medium in the light where hundreds of transgenic plantlets developed. The plants retained their stable transgenic state when grown in the greenhouse for two seasons. The transformation of O. dubium was similar in principle to that of L. longiflorum with three major differences: lily liquid-grown cultures grew more rapidly and had a higher potential for somatic embryo development. Ornithogalum cultures under selection took longer to develop into semi-organized cell clumps of sufficient size to allow continued shoot regeneration, were mostly organogenic, and the regenerated plantlets had higher rate of vitrification.