James E. Duffus

Tomato chlorosis virus: a new whitefly-transmitted, Phloem-limited, bipartite closterovirus of tomato.

ABSTRACT Tomato chlorosis virus (ToCV) is the second whitefly-transmitted, phloem-limited, bipartite closterovirus described infecting tomato. ToCV is distinct from tomato infectious chlorosis virus (TICV), based on lack of serological and nucleic acid cross-reactions and differences in vector specificity. TICV is transmitted only by the greenhouse whitefly (Trialeurodes vaporariorum), whereas ToCV is transmitted by the greenhouse whitefly, the banded-wing whitefly (T. abutilonea), and Bemisia tabaci biotypes A and B (B. argentifolii). Double-stranded (ds) RNA analyses of ToCV show two prominent dsRNAs of approximately 7,800 and 8,200 bp, with several small dsRNAs. Digoxigenin-11-UTP-labeled riboprobes derived from cDNA clones representing portions of RNAs 1 and 2 were used in Northern blot hybridizations to detect two large nonhomologous dsRNAs and a subset of smaller dsRNAs. These probes were used in dot blot hybridizations to detect ToCV in infected tomato. Inclusion bodies and cytoplasmic vesicles were consistently observed in phloem tissues of ToCV-infected Nicotiana clevelandii. Computer-assisted sequence analysis showed significant homology between ToCV clones that hybridize specifically with RNAs 1 and 2 and the lettuce infectious yellows virus methyltransferase of RNA 1 and the HSP70 heat shock protein homolog of RNA 2, respectively. Thus, ToCV is another member of the growing subgroup of bipartite closteroviruses transmitted by whiteflies.

Tomato infectious chlorosis virus - a new clostero-like virus transmitted by Trialeurodes vaporariorum

A previously undescribed virus disease of tomato, other crops and weed hosts was found in California. Affected tomato plants exhibited interveinal yellowing, necrosis and severe yield losses. Leaf dips and purified preparations contained closterovirus-like long flexuous, filamentous particles approximately 12×850–900 nm. The virus, designated as tomato infectious chlorosis virus (TICV), is transmitted in a semipersistent manner by the greenhouse whitefly,Trialeurodes vaporariorum. The host range of the virus is moderate (26 species in 8 plant families) but includes some important crops and ornamental species including tomato, (Lycopersicon esculentum), tomatillo (Physalis ixocarpa), potato (Solanum tuberosum), artichoke (Cynara scolymus), lettuce (Lactuca sativa) and petunia (Petunia hybrida). The virus has been found in a number of different locations in California and has a number of potential vehicles of movement including greenhouse grown ornamentals, tomato transplants, artichoke cuttings and potato seed. The virus has the potential to spread to other growing regions with resident populations of the greenhouse whitefly. The host range, particle size, insect transmission, and serology clearly distinguish TICV from previously described viruses.

Morphology of the sweet potato whitefly,Bemisia tabaci (Homoptera, Aleyrodidae) relative to virus transmission

The stylet bundle of the sweet potato whitefly,Bemesia tabaci, consists of paired mandibles and maxillae. The latter interlock to form the food and salivary canals. Its salivary system consists of paired primary and accessary glands in the thorax. Primary and accessory gland ducts on each side of the nerve cord fuse to form lateral ducts that course anteroventrally to the midline and continue in parallel down the hypopharynx to eventually fuse to form the single afferent duct of the salivary pump. Saliva exiting the pump via the efferent duct enters the salivary canal of the maxillae. Food from the maxillary food canal passes from the antecibarium to the postcibarium or sucking pump and, per os, to the pharynx and esophagus of the foregut. The esophagus extends from the head to the base of the abdomen where it and the anterior midgut intimately mingle with the anterior hindgut to form a filter chamber. The midgut then proceeds dorsocaudally before looping anteroventrally to join the hindgut. The latter gives off two fingerlike Malpighian tubules before entering the filter chamber, whence it proceeds dorsocaudally to the anus within the vasiform orifice. Where possible, the morphology ofBemisia is discussed in relation to plant virus transmission and the morphologies of more thoroughly studied homopteran vectors such as aphids and leafhoppers.

Lettuce chlorosis virus — A new whitefly-transmitted closterovirus

A previously undescribed viras disease of lettuce, sugarbeets, other crop and weed hosts was found in the southwest desert regions of U.S.A. Affected lettuce and sugarbeet hosts exhibited interveinal yellowing, stunting, rolling, and brittleness of affected leaves. Since 1990, yellowing symptoms on desert lettuce and sugarbeet were shown to be induced by a mixture of lettuce infectious yellows viras (LIYV) and this previously undescribed viras termed lettuce chlorosis viras (LCV). LCV is a closterovirus with flexuous, filamentous particles 800–850 nm long. The viras is transmitted efficiently by bothBemisia biotypes. LCV differs significantly from LIYV and other previously described viruses in host range (LCV does not infect the Cucurbitaceae), insect transmission, and serology.

The use of isozyme patterns to distinguish sweetpotato whitefly (Bemisia tabaci) biotypes

Recent collections ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) from California desert regions represent a mixture of biotypes. One biotype was identical to a culture originally obtained in 1981 and since maintained in the laboratory. The other and most prevalent biotype could not be distinguished morphologically but could be distinguished by esterase isozyme banding patterns. The banding patterns of the biotypes were not affected by culturing the whiteflies on different plant species. Different developmental stages, and adults of both sexes, had the same isozyme patterns.

Transmission Properties of Whitefly-Borne Criniviruses and Their Impact on Virus Epidemiology

Publisher Summary The genus Crinivirus is in the family Closteroviridae. The type member of this new genus is Lettuce infectious yellows virus (LIYV). Criniviruses have particle lengths that are roughly half the lengths reported for closteroviruses [4]. All viruses that have been assigned to the genus Crinivirus are transmitted by whiteflies, as opposed to aphids for members of the genus Closterovirus. The incidence and impact of viruses belonging to the genus Crinivirus are dependent on the interactions among several factors, including the virus itself, the host range of that virus, the specific whitefly vector(s), surrounding crops and weeds, and climatic conditions. Criniviruses are unique in that they are transmitted by one or more of the following whitefly species: B. tabaci biotype A (sweet potato whitefly, SPWF), B. tabaci biotype B (silverleaf whitefly, SLWF), Trialeurodes vaporariorum Westwood (greenhouse whitefly, GHWF), and Trialeurodes abutilonea Haldeman (banded wing whitefly BWWF). A unique characteristic of criniviruses is that some members can be transmitted by more than one whitefly vector species or biotype with different levels of efficiency. This chapter addresses criniviruses and their whitefly vectors, particularly the effect of transmission characteristics on their disease epidemiology. Knowledge of the vectors is crucial to the management of the diseases caused by these viruses.

Ecology and Control

Ecology and control of plant viruses should be stressed together, for it is through understanding the ecology and epidemiology of plant viruses and their vectors that we have been able to control successfully a number of important plant virus diseases. It will be seen that some of the ground covered here has been detailed from a different viewpoint in Chapter 7. However, we feel that some overlap is inevitable in putting control measures and their ecological basis in context.

Overwintering and monitoring of potato leafroll virus in some wild crucifers

A potato leafroll virus (PLRV) isolate has been successfully transmitted to and recovered from two wild crucifers,Sisymbrium altissimum L. (Jim Hill or tumble mustard) andCapsella. bursa-pastoris (L.) Medic. (shepherd’s purse) by the green peach aphid (GPA),Myzus persicae (Sulzer). Virus antigen in both plant species was found to be higher in root tissue than in foliar tissue, based on enzyme-linked immunosorbent assay (ELISA) determinations.C. bursa-pastoris was apparently a relatively poorer source of inoculum for the GPA thanS. altissimum. Using two geographically-separated biotypes ofC. bursa-pastoris, a Washington biotype was found to contain higher antigen titer in both leaf and root tissue than a California biotype, as determined by ELISA. Field studies demonstrated that both weed species can serve as overwintering sources of PLRVCompendioUn aislamiento del virus del enrollamiento de la hoja de la papa (PLRV) ha sido exitosamente transmitido y recobrado de dos crucífieras silvestres,Sisymbrium altissimum L. (Jim Hill o mostaza postrada)y Capsella bursa-pastoris (L.) Medic, (boisa de pastor) por el áfido verde del melocotonero (GPA),Myzus persicae (Sulzer). Basándose en determinaciones efectuadas con la prueba inmunológica ELISA se encontró que el antígeno del virus en ambas especies vegetales era más alto en los tejidos de las raíces que en los de las hojas.C. bursa-pastoris fue aparentemente una fuente más o menos pobre de inóculo para el GPA, en comparación conS. altissimum. Utilizando dos biotipos geográficamente separados deC. bursa-pastoris, se encontró que un biotipo de Washington tenía, tanto en los tejidos de la hoja como en los de la raíz, una concentratión más alta de antígeno que un biotipo de California, tal como quedó comprobado con la técnica ELISA. Estudios de campo demostraron que ambas malezas pueden servir como fuentes de invernacion del PLRV.

Transmission of the agent causing a melon yellowing disease by the greenhouse whitefly Trialeurodes vaporariorum in southeast Spain

AbstractThe agent causing a yellowing disease of melon (Cucumis melo), which results in severe losses in crops under plastic on the coastal plains of southeast Spain, was shown to be transmitted in a semipersistent manner by the greenhouse whitefly (Trialeurodes vaporariorum Westwood). The agent was transmitted by grafting, but not by mechanical inoculation or through seeds. The agent was acquired in the minimum period tested (2 h) and could infect plants in an infection feeding interval of 6 h. Capsella bursa-pastoris, Cucumis melo, C. sativus, Cucurbita moschata, Cichorium endivia, Lactuca sativa andTaraxacum officinale were found susceptible.Results suggest that the yellowing disease affecting melon crops in the southeast of Spain is due to a pathogen similar to beet pseudo yellows virus, but this has to be confirmed by serology.