Journal of the Department of Agriculture, Western Australia, Series 4 Volume 16 Number 1 March, 1975 Article 2 1-1-1975 Virus diseases in agriculture George McLean Follow this and additional works at: https://researchlibrary.agric.wa.gov.au/journal_agriculture4 Part of the Agronomy and Crop Sciences Commons, Entomology Commons, Horticulture Commons, and the Viticulture and Oenology Commons Recommended Citation McLean, George (1975) "Virus diseases in agriculture," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 16 : No. 1 , Article 2. Available at: https://researchlibrary.agric.wa.gov.au/journal_agriculture4/vol16/iss1/2 This article is brought to you for free and open access by Research Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 4 by an authorized administrator of Research Library. For more information, please contact [email protected]. Electron micrographs of virus particles. Photographs by courtesy of Dr. C. Bracker, Department of Botany and Plant Pathology, Purdue University, Indiana, U.S.A. Straight rod-shaped virus Virus diseases in agriculture By George D. McLean, some viruses have been shown to and viruses that are spread by mealy Plant Pathologist contain an enzyme. Viruses do not bugs are not spread by leafhoppers. reproduce by division, but the viral Some species of aphids transmit Viruses are extremely small par­ nucleic acid "orders" the plant cell many viruses while other species ticles which can only be seen with to produce virus particles. transmit only a few. Aphids spread an electron microscope. A virus is How plant viruses are spread is cucumber mosaic virus, watermelon present in a diseased plant as huge important since a virus disease can­ mosaic virus and potato leaf roll numbers of tiny particles within not be "cured" and we must control virus and many other viruses. Thrips the cells of the plant. Viruses which the spread in a crop. Viruses are transmit tomato spotted wilt virus are infectious can cause disease, spread in various ways: by insects which causes disease in tomato and and reproduce only inside the cells and mites, by nematodes and soil lettuce crops. of a living plant. fungi, by vegetative propagation, There are two types of aphid Preparations from virus-infected within seed and by handling of in­ transmission; non-persistent or sty­ leaves or from purified extracts fected plants in the field. In the let-borne and persistent or circula- made in the laboratory may be glasshouse many viruses are trans­ tive. Cucumber mosaic and water­ examined under the electron micro­ mitted by making a sap extract from melon mosaic viruses are transmit­ scope, and the particles may be infected plants and rubbing this ted in the non-persistent manner. viewed and photographed. Some extract on leaves of healthy plants The virus may be passed on to a particles are spherical; others are previously dusted with a mild abras­ healthy plant within minutes after rod-shaped while some are bacilli- ive such as finely divided carborun­ the aphid has fed on the diseased form. The simplest virus consists of dum powder. plant. The aphid only retains the a molecule of nucleic acid, usually Many insects transmit plant virus virus for a very short time. More ribonucleic acid, surrounded with a diseases—aphids, leafhoppers, simply, the virus adheres to an in­ protein coat. A small number of mealy bugs, thrips and beetles. sect's stylet after it feeds on an in­ viruses contain a molecule of deoxy­ Generally a virus is spread by only fected plant. ribonucleic acid plus a protein coat. one of these groups of insects. For Persistent or circulative trans­ Some viruses are more complex and example, those that are spread by mission means that there is a much contain lipid and in recent years aphids are not spread by thrips, longer period of time, from hours to 2 Journal of Agriculture Vol 16 No 1, 1975 . 1 Spherical-shaped virus rod-shaped virus days, between the aphid feeding on they have already infected the crop. programmes take many years to an infected plant and transmitting The symptoms of the disease will produce healthy stock. Virus-tested the disease to a healthy plant. appear some four to six weeks later. material is released to growers as Viruses transmitted in a persistent If the crop is infected when it is soon as it is available. manner have been observed in many young, the symptoms will be severe. In Western Australia, there are parts of the insect by electron There are a number of virus dis­ several viruses of fruit. Many grape­ microscopy. The insect retains the eases of subterranean clover in Wes­ vines are infected with grapevine virus for a long period of time from tern Australia. One of the most leafroll virus. Possibly the most days to months. Potato leaf roll recent diseases observed has been obvious symptom of this disease is virus is transmitted in this manner, red leaf virus, which is transmitted the failure of the red table grape, the aphid retaining the virus for its by an aphid. This virus also multi­ Red Emperor, to achieve its normal whole life after infection. plies in the aphid. Yarloop seems to red colour when infected with Efficient control will depend on be most severely affected, but other grapevine leafroll virus. The grower whether the aphids are carrying the cultivars are also affected. will also observe symptoms on the virus from an infected plant several Another important means of leaves: a scarlet or a red colour be­ hundred metres from the healthy virus spread is by vegetative pro­ tween the veins of the leaves of red crop, whether they are carrying the pagation in the orchard or the vine­ coloured fruit and a downward virus from an infected crop to a yard. If a healthy scion is budded rolling of the leaves. In other States bordering healthy crop, or whether onto an infected rootstock that and overseas, experiments have they are spreading the disease from healthy scion soon becomes infected shown that infected vines have plant to plant within a crop. with virus and the plant will then be smaller clusters, fewer clusters per It is important to spray with in­ diseased. Fruit growers should use vine and a reduced sugar content. secticides to control aphids as a the healthiest rootstock and scion Thus if the vines are severely affec­ preventative measure, rather than to material available. Scientists are ted by the disease there may be con­ await the appearance of the insects. continually working on plant im­ siderable yield losses for the grower. Once a grower sees aphids on his provement programmes to produce In apple orchards many growers crop of rockmelons, and if these virus-free selections of grapevines, have probably seen cream to yel­ aphids have carried a virus, then apples, stone fruit and citrus. Such low spots on the leaves of Jona- 3 Journal of Agriculture Vol 16 No 1, 1975 Plum line pattern virus on Beauty plums Grapevine leafroll disease on Red Emperor grapes Cucumber mosaic virus on cucumber. This aphid-transmitted virus affects many plants Passionfruit woodiness virus Stony pit disease on Josephine and Packham pears Lettuce big vein on lettuce Barley yellow dwarf virus on oats. This virus is aphid Tomato spotted wilt virus on lettuce, aphid transmitted transmitted Journal of Agriculture Vol 16 No 1, 1975 Red leaf virus of subterranean clover. This virus is Apple mosaic virus on Jonathan apple leaves transmitted by the potato aphid Maize dwarf mosaic virus on maize Rose mosaic virus on rose Subterranean clover stunt virus, aphid transmitted Camellia virus—flower break and leaf mottle Tomato big bud disease, caused by a mycoplasma and transmitted by leaf hoppers Apple green crinkle on Granny Smith apple • r 1 • "* Jr g * 4k • - * 45706—2 Journal of Agriculture Vol 16 No 1, 1975 thans. This disease is caused by one of which, lettuce big vein dis­ and adopt the most effective control apple mosaic virus. Another apple ease, is present in Western Australia. measures, the spread of virus dis­ virus disease is green crinkle, which Tobacco mosaic virus and potato eases can be reduced. The possi­ affects Granny Smith fruit. The virus X are highly infectious and bility of epidemics will be low. symptoms are severely distored fruit are easily spread in the field. Dis­ with depressed creases and irregular eased plants may be broken with Virus disease diagnosis in swellings on the surface of the fruit. the tractor wheels or implements. If Western Australia These diseases are transmitted by these damaged plants are moved The Western Australian Department the use of infected scions or root- through the crop, they may contact of Agriculture is expanding the stocks. and infect healthy plants. Tobacco diagnostic service for the identi­ In the potato industry, many virus mosaic virus can be present in dis­ fication of plant viruses. Until diseases are transmitted by the use eased tobacco. Smokers may spread recently this service has been the of infected seed. Potato leafroll and tobacco mosaic virus from their testing of diseased plants by inocu­ potato viruses X and S and to a hands to tomato plants. lating sap extracts on to indicator lesser extent potato virus Y are all Growers should attempt to plants in the glasshouse. Facilities transmitted through infected tubers. become aware of virus diseases on for the handling of aphids will be This is a very efficient means of "self-sown" plants. Any plants developed for vector transmission spread of viral diseases. It is there­ with disease symptoms should be studies. Some viruses are not sap- fore vital for seed growers to try to destroyed.