The occurrence and importance of okra mosaic virus in Nigerian weeds

The Nigerian National Horticultural Research Institute experimental and commercial farm has a long history of okra mosaic virus (OMV) disease. In an attempt to determine possible sources of inoculum, weeds growing within or around the vicinity of the farm were investigated. Several weeds showed virus or virus-like disease symptoms and mechanical inoculation of crude sap from three malvaceous weeds (Abutilon hirtum, Sida acuta, and Malvastrum coromandelianum) and one solanaceous weed (Physalis angulata) induced symptoms of OMV on okra test seedlings; serological tests confirmed the presence of OMV. Beetle vectors caught both from weeds and from okra were infective when confined on healthy okra seedlings for 48 h. Increase in the abundance of beetle vectors was accompanied by an increase in the incidence of OMV disease. The implications of these findings in the epidemiology and control of OMV are discussed.     

A freeze/thaw technique for estimation of nitrogenase activity in detached nodules of Vigna mungo

The Ivory Coast and Nigerian strains of okra mosaic virus (OMV) were transmitted by the flea-beetle Podagrica decolorata, a serious pest of okra in the southern Ivory Coast. The Ivory Coast strain was also transmitted by the orthopteran, Zonocerus variegatus. The Ivory Coast strain was acquired faster than it was inoculated by P. decolorata. When groups of five beetles were given acquisition and inoculation access periods of 24 and 48 h, respectively, 60% of the okra test plants were infected. OMV-carrying P. decolorata remained infective for up to 6 days. The virus was readily detected in extracts of crushed beetles that had fed on infected plants for 20 h. The beetle was also able to transmit to and from plants of Hibiscus sabdariffa and Corchorus olitorius; as a food source it preferred C. olitorius to okra or H. sabdariffa. The beetle is active throughout the year, and presumably can spread OMV at any time between plants of these species. A considerable and unexplained decrease in frequency of transmission was observed in experiments done in the rainy season. The revised cryptogram of OMV is R/l:*/32:S/S:S/Ve/Cl.     

Identification, purification and some properties of a mosaic virus of okra (Hibiscus esculentus)

In the Ivory Coast, an apparently undescribed virus was isolated from okra (Hibiscus esculentus) in which it caused mosaic and leaf vein banding. The virus was sap transmissible to a wide range of plants and had a thermal inactivation point of 80 °C. It was named okra mosaic virus (OMV). A purification procedure was developed. Electron microscopy and analytical and density gradient centrifugation showed that OMV was an isometric virus accompanied by empty shells (top component). Serological tests showed OMV to be a member of the tymovirus group.     

Effects of Simulated Oilfield Produced Water on Early Seedling Growth After Treatment in a Pilot-Scale Constructed Wetland System

Seed germination and early seedling growth bioassays were used to evaluate phytotoxicity of simulated oilfield produced water (OPW) before and after treatment in a subsurface-flow, pilot-scale constructed wetland treatment system (CWTS). Responses to untreated and treated OPW were compared among seven plant species, including three monocotyledons: corn (Zea mays), millet (Panicum miliaceum), and sorghum (Sorghum bicolor); and four dicotyledons: lettuce (Lactuca sativa), okra (Abelmoschus esculents), watermelon (Citrullus lanatus), and soybean (Glycine max). Phytotoxicity was greater in untreated OPW than in treated OPW. Exposures to untreated and treated OPW enhanced growth in some plant species (sorghum, millet, okra, and corn) relative to a negative control and reduced growth in other plant species (lettuce, soybean, and watermelon). Early seedling growth parameters indicated that dicotyledons were more sensitive to test waters compared to monocotyledons, suggesting that morphological differences between plant species affected phytotoxicity. Results indicated the following sensitivity scale for plant species: lettuce > soybean > watermelon > corn> okra≈millet >sorghum. Phytotoxicity of the treated OPW to lettuce and soybean, although concentrations of COCs were less than irrigation guideline concentrations, suggests that chemical characterization and comparison to guideline concentrations alone may not be sufficient to evaluate water for use in growing crops.     

Ants on swollen-thorn acacias: species coexistence in a simple system

 On the black cotton soils of the Laikipia ecosystem in Kenya, two swollen-thorn acacia species support nine ant species, four of which are apparently obligate plant-ants. Among the ants, there are five species of Crematogaster, two species of Camponotus, and one each of Tetraponera and Lepisota. Acacia drepanolobium is host to four ant species that are both common and mutually exclusive. These four ant species, and an additional non-exclusive ant species, tend to occur on trees of different sizes, implying a succession of ant occupants. Nonetheless, all four exclusive species occur in substantial proportions on trees of intermediate size. There is direct evidence that an early successional ant species (Tetraponera penzigi) is actively evicted by two late successional ant species in the genus Crematogaster. There was also some evidence of height differentiation among ant species resident on A. seyal. Different acacia-ant species had different direct effects on A. drepanolobium. Extrafloral nectaries were eaten and destroyed only on trees inhabited by Tetraponera. Axillary shoots were eaten only on trees inhabited by C. nigriceps (potentially another early successional ant). This was associated with more new terminal shoots and healthier leaves than other trees, but also the virtual elimination of flowering and fruiting. Different resident acacia-ant species also had characteristic relationships with other insects. Among the four mutually exclusive ant species, only Crematogaster sjostedti was associated with two species of Camponotus, at least one of which (C. rufoglaucus) appears to be a foraging non-resident. A. drepanolobium trees occupied by C. sjostedti were also far more heavily infested with leaf galls than were trees occupied by other ant species. A. drepanolobium trees occupied by C. mimosae and C. sjostedti uniquely had tended adult scale insects. This diversity of ant inhabitants, and their strikingly different relationships with their hosts and other insect species, are examples of coexisting diversity on an apparently uniform resource. Received: 13 November 1995 / Accepted: 16 May 1996     

Detection and relationships of cotton leaf curl virus and allied whitefly-transmitted geminiviruses occurring in Pakistan

A stock culture of cotton leaf curl virus from Pakistan (CLCuV-PK), was transmitted by whiteflies (Bemisia tabaci) to seven plant species, including French bean, okra, tobacco and tomato, and caused vein thickening and leaf curl symptoms. It was readily detected in triple antibody sandwich ELISA (TAS-ELIS A) by 11 out of 31 monoclonal antibodies raised against the particles of three other geminiviruses: African cassava mosaic, Indian cassava mosaic and okra leaf curl viruses. Reaction strength was enhanced when the tissue extraction fluid contained sodium sulphite. Minor variations in epitope profile were found among virus isolates from cotton (Gossypium hirsutum) collected from different districts in Pakistan over a 5-year period. These epitope profiles were distinguishable from that of cotton leaf curl virus from G. barbadense in southern India but indistinguishable from the profiles of viruses causing yellow vein disease of okra in India or Pakistan, or leaf curl of okra {Abelmoschus esculentus), Hibiscus tiliaceus, radish or sunflower in Pakistan, suggesting that these plants are putative natural hosts of CLCuV-PK. The viruses in cotton, and in okra with leaf curl or yellow vein symptoms, were also detected by PCR with three pairs of CLCuV-PK-specific primers. Five additional whitefly-transmitted geminiviruses were found among isolates from 11 other naturally-infected species in Pakistan, and were distinguished by their epitope profiles. These viruses were associated, respectively, with tobacco leaf curl, squash yellow blotch, tomato yellow leaf curl, watermelon leaf crinkle and soybean yellow mosaic diseases. The first four of these viruses were detected readily by PCR with geminivirus general primers but only weakly, if at all, with two pairs of CLCuV-PK-specific primers. Pakistani crops are infected with a range of distinguishable but relatively closely related whitefly-transmitted geminiviruses, some of which resemble those found in India.     

Increased Larval Growth and Preference for Virus-Infected Leaves by the Mexican Bean Beetle, Epilachna varivestis Mulsant, a Plant Virus Vector

Phaseolus vulgaris L. cv. 'Black Valentine' is a systemic host for the plant viruses Southern bean mosaic virus (SBMV) and bean pod mottle virus (BPMV). The Mexican bean beetle, Epilachna varivestis Mulsant, is a vector of SBMV and BPMV. Our objective was to determine if the interaction of SBMV and BPMV with 'Black Valentine' bean plants would affect beetle behavior and growth. In adult feeding preference test assays, beetles preferred and ingested more of the virus-infected bean leaf tissue than the noninfected leaf tissue. Beetle larvae that fed on SBMV- or BPMV-infected plants weighed more than those that fed on healthy plants. Our experiments suggest that there might be a mutually beneficial relationship between the beetle and the viruses that it vectors. The virus benefits from being transmitted and the beetle benefits from better larval growth when feeding on virus-infected leaf tissue. This study further demonstrates the complexity of relationships between multiple organisms.     

Recombination Among Begomoviruses on Malvaceous Plants Leads to the Evolution of Okra Enation Leaf Curl Virus in Pakistan

Whitefly transmitted begomoviruses (family Geminiviridae) are the major reason for significant yield losses of dicotyledonous crops in tropics and subtropics. Okra (Abelmoschus esculentus) is one of the important vegetable crops, and leaf curl disease caused by geminiviruses is the most important limiting factor for its production in Pakistan. Here, we report a new species of okra‐infecting begomovirus in south‐eastern region of Pakistan and the name Okra enation leaf curl virus (OELCuV) complex is proposed. This okra enation leaf curl disease complex (OELCuD) in Pakistan is found to be associated with Ageratum conyzoides symptomless alphasatellite (AConSLA). All efforts to clone the betasatellite were unsuccessful. Comprehensive sequence analyses suggest that intermalvaceous recombination between okra and cotton‐infecting begomoviruses resulted in the evolution of the new species. Surprisingly, Bhendi yellow vein mosaic virus (BYVMV) which has not been reported previously from Pakistan is the major parent while Cotton leaf curl Multan virus (CLCuMV) acts as a distant parent of the virus. Comparative recombination analysis also reveals that okra‐infecting begomoviruses from south and north‐western India is causing OELCuD in the Pakistan by recombining with CLCuMV at the Rep (1964–1513 nts). Recombination is common among geminiviruses and recombining of BYVMV and CLCuMV resulted in a new species: OELCuV. To the best of our knowledge, this evolution of a new species of okra‐infecting begomovirus is the first report of intermalvaceous recombination where Rep acts as the target region.     

Glitoria yellow vein virus, a tymovirus from Kenya

Clitoria yellow vein virus (CYW) was found in Clitoria ternatea and Abrus precatorius in coastal districts of Kenya, but was not detected in food legume crops. When transmitted by inoculation of sap, CYW infected many species in the Papilionaceae, commonly causing yellowing of secondary and smaller leaf veins. All the economically important food legumes grown in the area of occurrence were very susceptible, so that CYW is potentially very important. The virus also infected okra (Hibiscus esculentus) and species in the Solanaceae, but none of many species of Cucurbitaceae. CYW is serologically closely related to cocoa yellow mosaic and kennedya yellow mottle viruses, and more distantly to okra mosaic and desmodium yellow mottle viruses. Other properties of CYW^ typical of the tymoviruses include particle morphology (particle diameter c. 28 nm; two components) with sedimentation coefficients of 50S (top) and 109S (bottom); molecular weight of protein sub-units c. 20000; thermal inactivation point c. 72 ^oC; and longevity in vitro c. 3 wk.     

Aspects of prey relations in the coccidophagous ladybird <Emphasis Type="Italic">Chilocorus nigritus</Emphasis> relevant to its use as a biological control agent of scale insects in temperate glasshouses

The armoured scale insects Acutaspis umbonifera (Newstead), Pinnaspis buxi (Bouché) (Homoptera: Diaspididae) and the soft scale insects Saissetia coffeae (Walker) and Coccus hesperidum L. (Homoptera: Coccidae) were tested as suitable prey for the ladybird Chilocorus nigritus (F.) (Coleoptera: Coccinellidae), with a view to using the beetle as a biological control agent in UK glasshouses. C. nigritus larvae were able to complete development on all prey species tested and adults were also able to mature eggs on P. buxi, S. coffeae and C. hesperidum (A. umbonifera was not tested in this respect). Prey in ornamental glasshouses and interior landscapes are often diverse and patchily distributed. Thus the effect on the beetle larvae of switching between diaspidid and coccid prey was also examined. Larvae were able to switch from feeding on C. hesperidum to Abgrallaspis cyanophylli (Signoret) (Homoptera: Diaspididae) and vice versa with only minor detrimental effects when compared to those beetles reared throughout on one prey species. Introductions of C. nigritus as eggs, rather than adults are indicated for the control of soft scale species.     

Insect vectors of cowpea mosaic virus in Nigeria

A yellow strain of cowpea mosaic virus (CPMV) was transmitted in cowpea by two thrips, Sericothrips occipitalis and Taeniothrips sjostedti; two chrysomelid beetles, Ootheca mutabilis and Paraluperodes quaternus; a curculionid beetle, Nematocerus acerbus; and two acridid grasshoppers, Catantops spissus spissus and Zonocerus variegatus. Summarizing trials with single insects, the efficiency of transmission of CPMV averaged 18—21% for N. acerbus and the two grasshoppers, 55% for P. quaternus, and 71% for O. mutabilis. Twenty-two and 40% of the plants exposed to large populations of S. occipitalis and T. sjostedti, respectively, were infected. In three trials with an aphid, Aphis craccivora, 4 of 49 plants were infected with CPMV, but these infections were considered spurious because no infections occurred in any of 63 plants exposed to this insect in four other trials. A coreid bug, Riptortus dentipes, did not transmit CPMV. Mosaic symptoms in infected plants appeared 5—39 days after they were exposed to vectors. Infective virus was recovered from fresh faecal pellets of each grasshopper vector.     

Involvement of Volatile Substances in Systemic Resistance of Barley Against Erysiphe graminis f. sp. hordei Induced by Pruning of Leaves

Horsegram yellow mosaic disease was shown to be caused by a geminivirus; horsegram yellow mosaic virus (HYMV). The virus could not be transmitted by mechanical sap inoculation. Leaf dip and purified virus preparations showed geminate virus particles, measuring 15-18 * 30 nm. An antiserum for HYMV was produced and in enzyme-linked immunosorbent assay (ELISA) and immunosorbent electron microscopy (ISEM) tests HYMV was detected in leaf extracts of fieldinfected bambara groundnut, french bean, groundnut, limabean, mungbean, pigeonpea and soybean showing yellow mosaic symptoms. Bemisia tabaci fed on purified HYMV through a parafilm membrane transmitted the virus to all the hosts listed above but not to Ageratum conyzoides, okra, cassava, cowpea, Croton bonplandianus, Lab-lab purpureus, Malvastrum coromandalianum and tomato. No reaction was obtained in ELISA and ISEM tests between HYMV antibodies and extracts of plants diseased by whitefly-transmitted agents in India such as A. conyzoides yellow mosaic, okra yellow vein mosaic, C. bonplandianus, yellow vein mosaic, M. coromandalianum yellow vein mosaic, tomato leaf curl and cassava mosaic. HYMV was also not found to be related serologically to bean golden mosaic, virus.     

Blackfly vectors of zoonotic onchocerciasis in Japan

Studies of blackfly vectors of Onchocerca dewittei japonica Uni, Bain & Takaoka (Spirurida: Onchocercidae), a parasite of wild boar implicated in the aetiology of zoonotic onchocerciasis in Japan, and six other zoonotic Onchocerca species of this country are reviewed. Molecular identification of infective larvae found in wild‐caught female blackflies showed that Simulium bidentatum (Shiraki) (Diptera: Simuliidae) is a natural vector of O. dewittei japonica, and also Onchocerca sp. sensu Fukuda et al., another parasite of wild boar. Inoculation experiments demonstrated that Simulium arakawae Matsumura and four other Simulium species are putative vectors. Similarly, S. arakawae, S. bidentatum and Simulium oitanum (Shiraki) are putative vectors of Onchocerca eberhardi Uni & Bain and Onchocerca skrjabini Rukhlyadev, parasites of sika deer. Morphometric studies of infective larvae indicated that Onchocerca lienalis Stiles, a bovine species, is transmitted by S. arakawae, Simulium daisense (Takahasi) and Simulium kyushuense Takaoka, and that Onchocerca sp. sensu Takaoka & Bain, another bovine species, is transmitted by S. arakawae, S. bidentatum, S. daisense and S. oitanum. Prosimulium sp. (Diptera: Simuliidae) and Simulium japonicum Matsumura are suspected vectors of Onchocerca suzukii Yagi, Bain & Shoho and O. skrjabini [Twinnia japonensis Rubtsov (Diptera: Simuliidae) may also transmit the latter], parasites of Japanese serow, following detection of the parasites' DNA genes in wild‐caught blackflies.     

The mechanism of Pseudomonas aeruginosa outer membrane vesicle biogenesis determines their protein composition

Gram-negative bacteria produce outer membrane vesicles (OMVs) and contain bacterial cargo including nucleic acids and proteins. The proteome of OMVs can be altered by various factors including bacterial growth stage, growth conditions, and environmental factors. However, it is currently unknown if the mechanism of OMV biogenesis can determine their proteome. In this study, we examined whether the mechanisms of OMV biogenesis influenced the production and protein composition of Pseudomonas aeruginosa OMVs. OMVs were isolated from three P. aeruginosa strains that produced OMVs either by budding alone, by explosive cell lysis, or by both budding and explosive cell lysis. We identified that the mechanism of OMV biogenesis dictated OMV quantity. Furthermore, a global proteomic analysis comparing the proteome of OMVs to their parent bacteria showed significant differences in the identification of proteins in bacteria and OMVs. Finally, we determined that the mechanism of OMV biogenesis influenced the protein composition of OMVs, as OMVs released by distinct mechanisms of biogenesis differed significantly from one another in their proteome and functional enrichment analysis. Overall, our findings reveal that the mechanism of OMV biogenesis is a main factor that determines the OMV proteome which may affect their subsequent biological functions.     

Role of dung beetle feeding mechanisms in limiting the suitability of species as hosts for the nematode Spirocerca lupi

Various species of dung beetle serve as intermediate hosts after ingesting the embryonated eggs (11–15 × 30–37 µm) of Spirocerca lupi (Spirurida: Spirocercidae) in dog faeces. The feeding mechanisms of coprophagous dung beetles restrict the size of the food particles they can ingest and hence may determine which species can be efficient vectors for S. lupi. In this study, we aimed to exclude certain dung beetle species as possible hosts of S. lupi based on whether or not they ingested latex beads of known diameters mixed into fresh cattle dung. We found that the majority (11/14) of species tested can potentially serve as intermediate hosts of S. lupi because their mouthparts allow the passage of food particles larger than the minimum size range of the eggs of this parasite.     

Pathogen effects on vegetative and floral odours mediate vector attraction and host exposure in a complex pathosystem

Pathogens can alter host phenotypes in ways that influence interactions between hosts and other organisms, including insect disease vectors. Such effects have implications for pathogen transmission, as well as host exposure to secondary pathogens, but are not well studied in natural systems, particularly for plant pathogens. Here, we report that the beetle‐transmitted bacterial pathogen Erwinia tracheiphila – which causes a fatal wilt disease – alters the foliar and floral volatile emissions of its host (wild gourd, Cucurbita pepo ssp. texana) in ways that enhance both vector recruitment to infected plants and subsequent dispersal to healthy plants. Moreover, infection by Zucchini yellow mosaic virus (ZYMV), which also occurs at our study sites, reduces floral volatile emissions in a manner that discourages beetle recruitment and therefore likely reduces the exposure of virus‐infected plants to the lethal bacterial pathogen – a finding consistent with our previous observation of dramatically reduced wilt disease incidence in ZYMV‐infected plants.     

Amino acid deprivation and central carbon metabolism regulate the production of outer membrane vesicles and tubes by Francisella

Francisella tularensis is a highly virulent Gram‐negative bacterial pathogen that causes the zoonotic disease tularemia. F. novicida, a model tularemia strain, produces spherical outer membrane vesicles (OMV), as well as novel tubular vesicles and extensions of the cell surface. These OMV and tubes (OMV/T) are produced in a regulated manner and contain known virulence factors. Mechanisms by which bacterial vesicles are produced and regulated are not well understood. We performed a genetic screen in F. novicida to decipher the molecular basis for regulated OMV/T formation, and identified both hypo‐ and hyper‐vesiculating mutants. Mutations in fumA and tktA, involved in central carbon metabolism, and in FTN_0908 and FTN_1037, of unknown function, resulted in severe defects in OMV/T production. Cysteine deprivation was identified as the signal that triggers OMV/T formation in F. novicida during growth in rich medium. We also found that fully virulent F. tularensis produces OMV/T in a similarly regulated manner. Further analysis revealed that OMV/T production is responsive to deprivation of essential amino acids in addition to cysteine, and that the hypo‐vesiculating mutants are defective in responding to this signal. Thus, amino acid starvation, such as encountered by Francisella during host cell invasion, regulates the production of membrane‐derived structures.     

Comparative Studies on Aphid Transmission of the Sudanese Strain of Peanut Stunt Virus

The Sudanese strain of peanut stunt virus was transmitted by Aphis craccivora, Aphis solanella, Myzus persicae and Liaphis erysimi. Of these, A. solanella and L. erysimi were reported for the first time as vectors of peanut stunt virus. A. gossypii, A. solani and Rhopalosiphum maidis failed to transmit the virus. Viruliferous aphids retained the virus for 30 minutes but post-acquisition starvation beyond 30 minutes resulted in almost complete loss of the virus. A. craccivora transmitted the virus to four consecutive test plants and A. solanella, L. erysimi and M. persicae transmitted the virus to three consecutive test plants. It has been suggested that future research programmes should, include resistance to the virus in the major legume crops and that a crop like lucerne (Medicago sativa) which harbours both the virus and its vectors, should not be introduced in the major peanut-growing areas of the Sudan.