Natural Occurrence of Pepino mosaic virus in Lycopersicon Species in Central and Southern Peru

Pepino mosaic virus (PepMV), a potexvirus first described in 1980 from pepino ( Solanum muricatum ) plants cultivated in Peru, was isolated from diseased tomato plants in the Netherlands in 1999, and is now the cause of an emerging tomato disease in Europe. In a survey of central and southern Peru, 65 wild and four cultivated populations of Lycopersicon , as well as six populations of other species of Solanaceae , were tested for the presence of PepMV and six other viruses. Of the Lycopersicon population sampled, 23 (35.4%) reacted positively in double antibody sandwich (DAS)-enzyme-linked immunosorbent assay (ELISA) with antisera to PepMV. DAS-ELISA tests for PepMV of other solanaceous species were negative, except for one sample of pepino ( Solanum muricatum ). Mechanical inoculation of susceptible Lycopersicon esculentum cv. NE-1 plants with crude sap extracts of 20 of these samples confirmed that 15 of them (from the Departments of Apurimac, Arequipa and Moquegua) were infected with PepMV; these inoculated plants were also DAS-ELISA positive and, in most cases, developed symptoms. Thirteen of the infective extracts were obtained from plants of wild Lycopersicon species (three L. chilense , three L. chmielewskii , two L. parviflorum and five L. peruvianum ) and one each from the cultivated species L. esculentum and S. muricatum . The wild Lycopersicon species are newly reported natural hosts of PepMV. Tests for the other six viruses were negative, except that two samples contained Tomato mosaic virus . Thus, PepMV occurs in Lycopersicon species in central and southern Peru, even in isolated wild populations. These results indicate that the virus is not new to the region and has an efficient mechanism of natural transmission.     

Vectoring of Pepino mosaic virus by bumble‐bees in tomato greenhouses

Pepino mosaic virus (PepMV) has become an important viral disease of greenhouse tomatoes worldwide. The ability of bumble‐bees (Bombus impatiens), used for pollination, to acquire and transmit PepMV was investigated, and the prevalence of PepMV in plants and bumble‐bees in commercial tomato greenhouses was determined. PepMV infection in plants was determined using enzyme‐linked immunosorbent assay, while in bumble‐bees direct real‐time PCR was used. In the first experiment, the bumble‐bees were exposed for 14 days to PepMV‐infected plants. After 14 days, almost all bumble‐bees were PepMV positive both in the hive (78.5 ± 17.5%) and in the flowers (96.3 ± 3.6%). In the second experiment, bumble‐bees were released into a greenhouse with both PepMV‐infected source plants and healthy non‐infected target plants for 14 days. At the end of the experiment, 61.0 ± 19.5% of the bees collected from the hive and 83.3 ± 16.7% of the bees sampled from the flowers were PepMV positive. Bumble‐bees transmitted PepMV from the infected to the healthy non‐infected tomato plants. Two weeks after bumble‐bee release, the virus was detected in leaf, fruit and flower samples of formerly healthy plants. After 6 weeks, the percentage of PepMV positive samples from the target plants increased to 52.8 ± 2.8% of the leaves and 80.6 ± 8.4% of the fruits. In the control greenhouse without bumble‐bees, the target plants did not become infected. Based on the infection levels in flowers, fruits and leaves, the PepMV infection occurred possibly first in the pollinated flowers, and then spread from the fruit that developed from the flowers to other parts of the plant. In commercial greenhouses where PepMV was present, 92–100% of the plants and 88–100% of the bumble‐bees were PepMV positive. No infected plant samples were found in the control commercial greenhouse, but a small number of bumble‐bees (10%) tested PepMV positive.     

Transmission of Pepino mosaic virus by the Fungal Vector Olpidium virulentus

Transmission of Pepino mosaic virus (PepMV) by the fungal vector Olpidium virulentus was studied in two experiments. Two characterized cultures of the fungus were used as stock cultures for the assay: culture A was from lettuce roots collected in Castellón (Spain), and culture B was from tomato roots collected in Murcia (Spain). These fungal cultures were maintained in their original host and irrigated with sterile water. The drainage water collected from irrigating these stock cultures was used for watering PepMV‐infected and non‐infected tomato plants to constitute the acquisition–source plants of the assay, which were divided into six different plots: plants containing fungal culture A (non‐infected and PepMV‐infected); plants containing fungal culture B (non‐infected and PepMV‐infected); PepMV‐infected plants without the fungus; and plants non‐infected either with PepMV and the fungus. Thirty‐six healthy plants grouped into six plots, which constituted the virus acquisition–transmission plants of the assay, were irrigated with different drainage waters obtained by watering the different plots of the acquisition–source plants. PepMV was only transmitted to plants irrigated with the drainage water collected from PepMV‐infected plants whose roots contained the fungal culture B from tomato with a transmission rate of 8%. No infection was detected in plants irrigated with the drainage water collected from plots with only a fungus or virus infection. Both the virus and fungus were detected in water samples collected from the drainage water of the acquisition–source plants of the assay. These transmission assays demonstrated the possibility of PepMV transmission by O. virulentus collected from tomato crops.     

Pepino mosaic virus triple gene block protein 1 (TGBp1) interacts with and increases tomato catalase 1 activity to enhance virus accumulation

Various plant factors are co‐opted by virus elements (RNA, proteins) and have been shown to act in pathways affecting virus accumulation and plant defence. Here, an interaction between Pepino mosaic virus (PepMV) triple gene block protein 1 (TGBp1; p26) and tomato catalase 1 (CAT1), a crucial enzyme in the decomposition of toxic hydrogen peroxide (H₂O₂), was identified using the yeast two‐hybrid assay, and confirmed via an in vitro pull‐down assay and bimolecular fluorescent complementation (BiFC) in planta. Each protein was independently localized within loci in the cytoplasm and nuclei, sites at which their interaction had been visualized by BiFC. Following PepMV inoculation, CAT mRNA and protein levels in leaves were unaltered at 0, 3 and 6 days (locally) and 8 days (systemically) post‐inoculation; however, leaf extracts from the last two time points contained increased CAT activity and lower H₂O₂ levels. Overexpression of PepMV p26 in vitro and in planta conferred the same effect, suggesting an additional involvement of TGBp1 in potexvirus pathogenesis. The accumulation of PepMV genomic and subgenomic RNAs and the expression of viral coat protein in noninoculated (systemic) leaves were reduced significantly in CAT‐silenced plants. It is postulated that, during PepMV infection, a p26–CAT1 interaction increases H₂O₂ scavenging, thus acting as a negative regulator of plant defence mechanisms to promote PepMV infections.     

Pepino mosaic virus: a successful pathogen that rapidly evolved from emerging to endemic in tomato crops

Taxonomy: Pepino mosaic virus (PepMV) belongs to the Potexvirus genus of the Flexiviridae family. Physical properties: PepMV virions are nonenveloped flexuous rods that contain a monopartite, positive‐sense, single‐stranded RNA genome of 6.4 kb with a 3′ poly‐A tail. The genome contains five major open reading frames (ORFs) encoding a 164‐kDa RNA‐dependent RNA polymerase (RdRp), three triple gene block proteins of 26, 14 and 9 kDa, and a 25‐kDa coat protein. Genome diversity: Four PepMV genotypes, with an intergenotype RNA sequence identity ranging from 78% to 95%, can be distinguished: the original Peruvian genotype (LP); the European (tomato) genotype (EU); the American genotype US1; and the Chilean genotype CH2. Transmission: PepMV is very efficiently transmitted mechanically, and a low seed transmission rate has been demonstrated. In addition, bumblebees have been associated with viral transmission. Host range: Similar to other Potexviruses, PepMV has a rather narrow host range that is thought to be largely restricted to species of the Solanaceae family. After originally being isolated from pepino (Solanum muricatum), PepMV has been identified in natural infections of the wild tomato species S. chilense, S. chmielewskii, S. parviflorum and S. peruvianum. PepMV is causing significant problems in the cultivation of the glasshouse tomato Solanum lycopersicum, and has been identified in weeds belonging to various plant families in the vicinity of tomato glasshouses. Symptomatology: PepMV symptoms can be very diverse. Fruit marbling is the most typical and economically devastating symptom. In addition, fruit discoloration, open fruit, nettle‐heads, leaf blistering or bubbling, leaf chlorosis and yellow angular leaf spots, leaf mosaic and leaf or stem necrosis have been associated with PepMV. The severity of PepMV symptoms is thought to be dependent on environmental conditions, as well as on the properties of the viral isolate. Minor nucleotide sequence differences between isolates from the same genotype have been shown to lead to enhanced aggressiveness and symptomatology. Control: Prevention of infection through strict hygiene measures is currently the major strategy for the control of PepMV in tomato production. Cross‐protection can be effective, but only under well‐defined and well‐controlled conditions, and the effectiveness depends strongly on the PepMV genotype.     

Epidemic Spread of the Rust Fungus Puccinia lagenophorae and its Impact on the Competitive Ability of Senecio vulgaris in Celeriac During Early Development

The 'system management approach' of biological weed control was applied in a small-scale field experiment with celeriac (root celery), intersown with an inbred line of the annual weed Senecio vulgaris L. The naturalized rust fungus Puccinia lagenophorae Cooke (Basidiomycetes: Uredinales), a common and widespread pathogen of S. vulgaris in Europe, was introduced into parts of the plots, and its impact on the competitive balance between the crop and weed in the presence and absence of an additional herbicide treatment was studied. Competition by S. vulgaris (at a realized density of only 50 plants/m2) during the first 10 weeks of growth was substantial, reducing the fresh weight of the celeriac bulbs by 28%. The epidemic spread of the rust fungus was relatively fast, and the time to infection was similar to that in full-area applications. Inoculation with the rust fungus strongly reduced crop losses due to competition with S. vulgaris . The fresh weight of the celeriac bulbs in plots with both S. vulgaris and the fungus was not statistically diVerent from the celeriac yield in plots without S. vulgaris . This eVect was mainly the result of the reduced biomass of S. vulgaris , and not reduced survival. Infected plants may, therefore, still contribute to soil cover and may help to suppress later germinating weed species. Older plant stages were found to be infected earlier than younger stages. No significant interactions were observed between the eVects of the fungal infection and a low-dose application of the herbicide chlorbromuron on weed performance. Basic studies necessary to develop the system management approach further are discussed.     

Some Etiological Characteristics of Xanthomonas campestris pv. sesami and Disease Reaction of Different Sesame Cultivars

Abstract Isolates of X. campestris pv. sesami used in the present work behaved almost similarly on the basis of their morphological, biochemical and physiological characterization. The studies failed to differentiate any strains within the isolates.
Pathogenicity of the isolates to sesame plants was proved by inoculation experiments. When other plant species were inoculated infection did not occur.
The levels of resistance of some naturally selected sesame cultivars were investigated following artificial infection with the pathogen. Seven cultivars proved resistant, three ( cvs Tozi 3, S-76F₂-22 and K 112) were highly resistant.     

Reactions of some cucurbitaceous species Tozucchini yellow mosaic virus (ZYMV)

Zucchini yellow mosaic virus (ZYMV) is a widespread serious pathogen of cucurbitaceous plants. ZYMV was first detected in Hungary in 1995. Since then it has become one of the most dangerous viruses of the Cucurbitaceae family causing serious epidemics. The virus has many hosts, which - particularly perennial ones - may play important role as virus reservoirs and infection sources in virus epidemiology. On the other hand wild weed species maybe sources of resistance to viruses. Our research was carried out on a total of 15 wild species from 8 genera (Cucumis, Cucurbita, Cyclanthera, Ecballium Momordica, Lagenaria, Zehneria, Bryonia). Test plants were mechanically inoculated with ZYMV. Local and systemic symptoms were determined and 5 weeks after inoculation DAS-ELISA tests were also carried out. Symptomless plants were reinoculated to Cucumis sativus cv. Accordia test plants. On the basis of the results we determined the percentages of infections and so we classified the test-plants into sensitive and resistance categories. On the basis of the results new host plants of ZYMV are the followings: Bryonia dioica, Cyclanthera pedata, Ecballium elaterium, Momordica balsamina, Momordica rostrata, and Zehneria scabra. Among them Momordica balsamina and Ecballium elaterium showed latent to ZYMV. Bryonia alba and Zehneria indica are especially remarkable, because they proved resistant to ZYMV on the basis of symptomatology and serology. Our results might have significant role in the field of research of host range, virus resistance and virus differentiation.     

Host-plant selectivity of rhizobacteria in a crop/weed model system

Belowground microorganisms are known to influence plants' performance by altering the soil environment. Plant pathogens such as cyanide-producing strains of the rhizobacterium Pseudomonas may show strong host-plant selectivity. We analyzed interactions between different host plants and Pseudomonas strains and tested if these can be linked to the cyanide sensitivity of host plants, the cyanide production of bacterial strains or the plant identity from which strains had been isolated. Eight strains (four cyanide producing) were isolated from roots of four weed species and then re-inoculated on the four weed and two additional crop species. Bacterial strain composition varied strongly among the four weed species. Although all six plant species showed different reductions in root growth when cyanide was artificially applied to seedlings, they were generally not negatively affected by inoculation with cyanide-producing bacterial strains. We found a highly significant plant species x bacterial strain interaction. Partitioning this interaction into contrasts showed that it was entirely due to a strongly negative effect of a bacterial strain (Pseudomonas kilonensis/brassicacearum, isolated from Galium mollugo) on Echinochloa crus-galli. This exotic weed may not have become adapted to the bacterial strain isolated from a native weed. Our findings suggest that host-specific rhizobacteria hold some promise as biological weed-control agents.     

Pepino mosaic virus, a new potexvirus from pepino (Solanum muricatum)

Pepino mosaic virus (PepMV), a previously undescribed virus, was found in fields of pepino (Solanum muricatum) in the Canete valley in coastal Peru. PepMV was transmitted by inoculation of sap to 32 species from three families out of 47 species from nine families tested. It caused a yellow mosaic in young leaves of pepino and either a mild mosaic or symptomless infection in 12 wild potato species, five potato cultivars and potato clone USDA 41956 but S. stoloniferum and potato cultivars Merpata and Revolucion reacted with severe systemic necrotic symptoms. The virus was transmitted by plant contact but not by Myzus persicae. It was best propagated and assayed in Nicotiana glutinosa. Sap from infected N. glutinosa was infective after dilution to 10^-1 but not 10^-6, after 10 min at 65°C but not 70°C and after 3 months at 20°C. PepMV had filamentous particles with a normal length of 508 nm; the ends of some seemed damaged. Ultra-thin sections of infected leaves of N. glutinosa revealed many inclusions containing arrays of virus-like particles some of which were banded or whorled; small aggregates of virus-like particles were also common. The virus was purified by extracting sap from infected leaves in a solution containing 0·065 M disodium tetraborate, 0·435 M boric acid, 0·2% ascorbic acid and 0·2% sodium sulphite at pH 7·8, adding silver nitrate solution to the extract, and precipitating the virus with polyethylene glycol followed by two cycles of differential centrifugation. Particles of PepMV normally yielded two proteins with molecular weights of 26 600 and 23 200, but virus obtained from infective sap aged overnight yielded only the smaller protein suggesting that it was a product of degradation of the larger one. The virus is serologically related to two potexviruses, narcissus mosaic and cactus X and its properties are typical of the potexvirus group.     

Identification of potential hosts plants of Cowpea aphid‐borne mosaic virus

Among the major pathogens affecting passion fruit orchards, the cowpea aphid‐borne mosaic virus (CABMV), also known as the fruit‐hardening virus, has gained prominence owing to its role in the drastic reduction in fruit production in yellow passion fruit orchards (Passiflora edulis f. flavicarpa) from the second year of cultivation. To mitigate the damage, several regions adopt the annual planting system where a sanitary void is maintained from August to September. However, the virus is believed to remain dormant in weeds. This study aimed to identify potential weed hosts of CABMV. The study was conducted with a randomized design with four replications in Londrina, PR. Twenty‐eight weed species were tested, and a sample of yellow passion fruit leaves symptomatic for CABMV infection was used as the virus inoculum source. Mechanical inoculation was performed using the extract from the symptomatic plant. Symptoms were visually evaluated every 3 days. For molecular confirmation, total RNA was extracted, followed by RT‐PCR with CABMV‐specific oligonucleotides, reinoculation in passion fruit plants and sequencing. CABMV infection was observed in southern sandbur (Cenchrus echinatus), Siberian motherwort (Leonurus sibiricus), showy rattlepod (Crotalaria spectabilis) and yellow passion fruit (Passiflora edulis). The CABMV‐positive weed species extract was able to infect yellow passion fruit plant when a fresh mechanical inoculation was performed. Showy rattlepod (Crotalaria spectabilis) was the only weed species to exhibit observable symptoms of CABMV. C. echinatus, L. sibiricus and C. spectabilis act as a source of CABMV inoculum.     

Factors Affecting Disease Development by Rhynchosporium alismatis in Starfruit (Damasonium minus), a Weed of Rice

The fungal pathogen Rhynchosporium alismatis is being developed for biological control of starfruit (Damasonium minus), an important aquatic weed in Australian rice fields. The development of R. alismatis in starfruit differs between juvenile and adult plants. Juvenile starfruit plants are stunted as a result of fungal infection, while in adult plants, the main effect is necrosis and chlorosis of floating leaves. A conidial concentration of 1×10⁴ conidia mL^-1 was adequate to cause disease symptoms on floating leaves, but the stunting effect on juveniles was caused by concentrations of at least 1×10⁵ conidia mL^-1. To successfully inoculate juvenile plants, the water must be drained before inoculation to expose plants to the inoculum. The artificial addition of dew periods did not enhance disease development in plants. The stunting of juvenile starfruit plants caused by the infection of R. alismatis may give rice plants a competitive advantage over the weed at the seedling stage     

Effect of an alternate weed host, hairy nightshade, Solanum sarrachoides, on the biology of the two most important potato leafroll virus (Luteoviridae: Polerovirus) vectors, Myzus persicae and Macrosiphum euphorbiae (Aphididae: Homoptera)

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.     

New Necrotic Isolates of Pepino mosaic virus Representing the Ch2 Genotype

New necrotic isolates of Pepino mosaic virus (PepMV) were found in 2007 infecting greenhouse tomato plants in Poland. The isolates differ from previously identified PepMV isolates in host range and symptomatology. They induce severe necrosis on tomato plants ( Solanum lycopersicum ) and local necrotic lesions on Datura inoxia . Phylogenetic analysis, based on three distinct regions, triple gene block 1, the coat protein gene and a part of polymerase gene, revealed that the new necrotic isolates share high nucleotide sequence identity with isolates of the Ch2 genotype. This is the first report describing a necrotic type of PepMV of the Ch2 genotype.     

Survival and Transmission of Potato Virus Y,Pepino Mosaic Virus,and Potato Spindle Tuber Viroid in Water

Hydroponic systems and intensive irrigation are used widely in horticulture and thus have the potential for rapid spread of water-transmissible plant pathogens. Numerous plant viruses have been reported to occur in aqueous environments, although information on their survival and transmission is minimal, due mainly to the lack of effective detection methods and to the complexity of the required transmission experiments. We have assessed the role of water as a source of plant infection using three mechanically transmissible plant pathogens that constitute a serious threat to tomato and potato production: pepino mosaic virus (PepMV), potato virus Y (PVY), and potato spindle tuber viroid (PSTVd). PepMV remains infectious in water at 20 ± 4°C for up to 3 weeks, PVY (NTN strain) for up to 1 week, and PSTVd for up to 7 weeks. Experiments using a hydroponic system show that PepMV (Ch2 genotype) and PVY (NTN strain) can be released from plant roots into the nutrient solution and can infect healthy plants through their roots, ultimately spreading to the green parts, where they can be detected after a few months. In addition, tubers developed on plants grown in substrate watered with PSTVd-infested water were confirmed to be the source of viroid infection. Our data indicate that although well-known pathways of virus spread are more rapid than water-mediated infection, like insect or mechanical transmission through leaves, water is a route that provides a significant bridge for rapid virus/viroid spread. Consequently, water should be taken into account in future epidemiology and risk assessment studies.     

Favourable Conditions for the Bioherbicide Candidate Fusarium tumidum to Infect and Cause Severe Disease on Gorse (Ulex europaeus) in a Controlled Environment

The development of the pathogenic fungus Fusarium tumidum on gorse ( Ulex europaeus ), a major weed of pastures and plantation forests in New Zealand, was studied under controlled conditions. F. tumidum , like most other foliar fungal pathogens, requires moisture to infect plants. Long, continuous dew periods ( 24 h) after inoculation of plants provided favourable conditions for infection. The fungus, however, also caused severe disease on young plants (2 months old) exposed to two or three 12-h dew periods interrupted by 12-h dry periods. A delay of 24 h before inoculated plants were exposed to dew did not affect the severity of the disease. F. tumidum infected plants over a wide range of temperatures (5-27IC), but more plants were killed as temperatures increased during the initial infection phase. All gorse plants tested (up to 4 months old) were susceptible to the fungus, but younger plants were more easily killed. Nevertheless, the biomass of older plants that were severely diseased but not killed by the fungus was significantly reduced. The effectiveness of F. tumidum in killing plants increased with the density of inoculum sprayed. The fungus applied at a density of 1 106 conidia/ml killed more than 95% of 1.5-month-old plants. This basic knowledge of the F. tumidum -gorse system will assist in the development of a pilot bioherbicide to control gorse and broom ( Cytisus scoparius ), another economically important weed in New Zealand which is also susceptible to the fungus.     

Selection of perennial and Italian ryegrass plants resistant to ryegrass mosaic virus

Perennial ryegrass plants collected from fields and Italian ryegrass plants grown from seed were selected for resistance to infection by ryegrass mosaic virus (RMV) by repeated manual inoculation. Two of 108 perennial ryegrass plants and one of 150 Italian ryegrass plants were symptomless after seven and nine inoculations respectively. These three plants were propagated vegetatively. Plants of the two perennial ryegrass clones showed no symptoms after further manual inoculations with the initial isolate of RMV, or with an inoculum from infected plants collected from several fields, or after inoculation by viruliferous mites. Electron microscopy and back tests indicated that the plants were virus free. Some plants of the selected Italian ryegrass clone became infected after a further inoculation with mites or sap, but fewer than similarly inoculated unselected plants.