Western Plant Diagnostic Network1 First Detector News A Quarterly Pest Update for WPDN First Detectors Spring 2015 edition, volume 8, number 2 In this Issue Page 1: Editor’s Note Dear First Detectors, Pages 2 – 3: Intro to Plant Plant viruses cause many important plant diseases and are Viruses responsible for huge losses in crop production and quality in Page 4: Virus nomenclature all parts of the world. Plant viruses can spread very quickly because many are vectored by insects such as aphids and Page 5 – Most Serious World Plant Viruses & Symptoms whitefly. They are a major pest of crop production as well as major pests of home gardens. By mid-summer many fields, Pages 6 – 7: Plant Virus vineyards, orchards, and gardens will see the effects of plant Vectors viruses. The focus of this edition is the origin, discovery, taxonomy, vectors, and the effects of virus infection in Pages 7 - 10: Grapevine plants. There is also a feature article on grapevine viruses. Viruses And, as usual, there are some pest updates from the West. Page 10: Pest Alerts On June 16 – 18, the WPDN is sponsoring the second Invasive Snail and Slug workshop at UC Davis. The workshop Contact us at the WPDN Regional will be recorded and will be posted on the WPDN and NPDN Center at UC Davis: home pages. Have a great summer and here’s hoping for Phone: 530 754 2255 rain! Email: [email protected] Web: https://wpdn.org Please find the NPDN family of newsletters at: Editor: Richard W. Hoenisch @Copyright Regents of the Newsletters University of California All Rights Reserved Western Plant Diagnostic Network News Plant Viruses 2 Ag, Manitoba Photo courtesy Photo Food, and Rural Initiatives and Food, of APS Photo by Giovanni Martelli, U of byBari Giovanni Photo Grapevine Fanleaf Virus Peanut leaf with Squash Mosaic Virus tomato spotted wilt virus Viruses are infectious pathogens that are too small to be seen with a light microscope, but despite their small size they can cause chaos. The simplest viruses are composed of a small piece of nucleic acid surrounded by a protein coat. As is the case with other organisms, viruses carry genetic information in their nucleic acid which typically specifies three or more proteins. All viruses are obligate parasites that depend on the cellular machinery of their hosts to reproduce. Viruses are not active outside of their hosts, and this has led some people to suggest that they are not alive. All types of living organisms including animals, plants, fungi, and bacteria are hosts for viruses, but most viruses infect only one type of host. Viruses cause many important plant diseases and are responsible for losses in crop yield and quality in all parts of the world. Photo courtesy APS Photo of Image APS of courtesy Electron micrograph of the TMV in action in tobacco actual TMV virus Most viruses are restricted to a particular type of host. Some infect bacteria, and are known as bacteriophages, whereas others are known that infect algae, protozoa, fungi (mycoviruses), invertebrates, vertebrates or vascular plants. However, some viruses that are transmitted between vertebrate or plant hosts by feeding insects (vectors) can replicate within both their host and their vector. This web site is mostly concerned with those viruses that infect plants but we also provide some taxonomic and genome information about viruses of fungi, protozoa, vertebrates and invertebrates where these are related to plant viruses. Viruses cause many diseases of international importance. Amongst the human viruses, smallpox, polio, influenza, hepatitis, human immunodeficiency virus (HIV-AIDS), measles and the SARS coronavirus are particularly well known. While antibiotics can be very effective against diseases caused by bacteria, these treatments are ineffective against viruses and most control measures rely on vaccines (antibodies raised against some component of the virus) or relief of the symptoms to encourage the body's own defense system. Western Plant Diagnostic Network News 3 Viruses also cause many important plant diseases and are responsible for huge losses in crop production and quality in all parts of the world. Infected plants may show a range of symptoms depending on the disease but often there is leaf yellowing (either of the whole leaf or in a pattern of stripes or blotches), leaf distortion (e.g. curling) and/or other growth distortions (e.g. stunting of the whole plant, abnormalities in flower or fruit formation). Some important animal and human viruses can be spread through aerosols. The viruses have the "machinery" to enter the animal cells directly by fusing with the cell membrane (e.g. in the nasal lining or gut). By contrast, plant cells have a robust cell wall and viruses cannot penetrate them unaided. Most plant viruses are therefore transmitted by a vector organism that feeds on the plant or (in some diseases) are introduced through wounds made, for example, during cultural operations (e.g. pruning). A small number of viruses can be transmitted through pollen to the seed (e.g. barley stripe mosaic virus, genus Hordeivirus) while many that cause systemic infections accumulate in vegetatively-propagated crops. Tobacco Mosaic Virus: A Virus with a History 1. 1. Adolf Mayer Martinus Beijerinck Dmitri Ivanovsky The discovery of plant viruses causing disease is often accredited to Adolf Mayer (1886) working in the Netherlands demonstrated that the sap of mosaic obtained from tobacco leaves developed mosaic symptom when injected in healthy plants. However the infection of the sap was destroyed when it was boiled. He thought that the causal agent was the bacteria. However, after larger inoculation with a large number of bacteria, he failed to develop a mosaic symptom. In 1898, Martinus Beijerinck , who was a Professor of Microbiology at the Technical University the Netherlands, and at the same time Dmitri Ivanovsky in the Crimea put forth their concepts that viruses were small and determined that the "mosaic disease" remained infectious when passed through a Chamberland filter . This was in contrast to bacteria microorganisms, which were retained by the filter. Beijerinck referred to the infectious filtrate as a “Contagium vivum fluidum ", thus the coinage of the modern term "virus". Plant pathologists are always very proud that the discovery of tobacco mosaic virus was the first virus in all biology to be so identified. The investigations of tobacco mosaic disease and subsequent discovery of its viral nature were instrumental in the establishment of the general concepts of virology. TMV was the first virus to be crystalized in 1935 by Wendell Meredith Stanley at UC Berkeley, for which he won the Nobel Prize. Stanley found that TMV remained infectious even after crystallization! Wendell Meredith Stanley Western Plant Diagnostic Network News Virus Naming and Classification Binomial nomenclature , with genus and species, is standard in the world of biology – except with common 4 virus names. Most plant viruses are named by their hosts and symptoms, such as tobacco mosaic virus, eggplant yellow mosaic, grapevine fan leaf virus, barley yellow dwarf, and peanut stunt virus. However, there is a method behind this possible confusion. The common names originated from the first plant the virus symptoms were noted, such as tobacco mosaic virus. However as the science of virology advanced, similarities and a tremendous diversity among viruses were noted and they were assigned to orders and family groups, as in binomial nomenclature. Starting in 1971, International Committee on Taxonomy of Viruses (ICTV) began to standardize virus taxonomy, thus organizing the confusion brought about by only common names. See also Virus family groups for all the known plant, animal, and human viruses. Chart courtesy of the Australian Ministry of Agriculture Note the different symptoms on the same plant cultivar Western Plant Diagnostic Network News The Top World Plant Viruses 5 1. Tobacco mosaic virus The common names of viruses came from the plant species in 2. Tomato spotted wilt virus which a virus was first observed. However, this doesn’t 3. Tomato yellow leaf curl virus necessarily mean the virus is limited just to that one particular 4. Cucumber mosaic virus plant. Cauliflower mosaic virus (CaMV) (notice the shorthand) 5. Potato virus Y was first found on cauliflower, CaMV infects mostly plants of 6. Cauliflower mosaic virus the Brassicaceae family, but some CaMV strains (D4 and W260) 7. African cassava mosaic virus are also able to infect Solanaceae species of the genera Datura 8. Plum pox virus and Nicotiana . Barley yellow dwarf is a plant disease caused by 9. Brome mosaic virus the barley yellow dwarf virus (BYDV), and is the most widely 10. Potato virus X distributed viral disease of cereals. It affects the economically 11. Citrus tristeza virus important crop species barley, oats, wheat, maize, triticale and 12. Barley yellow dwarf virus rice. As you click on each virus group, notice the crops each 13. Potato leafroll virus virus infects and the very modern virology nomenclature used. 14. Tomato bushy stunt virus 15. Grapevine leafroll virus complex 16. Grapevine fanleaf virus 17. Rose rosette virus Photo courtesy FarmingUK Photo of Photo courtesy Photo APS Photo courtesy Photo APS Potato leafroll virus Potato Y virus Left, barley yellow dwarf virus affected plant; right a resistant variety Photos courtesyPhotos APS Photo courtesy Photo APS Photos by EP Rybicki Photos African cassava mosaic Tomato yellow leaf curl Plum pox virus: Leaves and fruit showing virus: Severe leaf distortion virus affected tomato chlorotic and necrotic ring patterns, and and mosaic and leaf loss in chlorotic blotches. A) Chlorotic ring patterns cassava in western Kenya in peach fruit; B) Chlorotic blotches in peach leaves; C) Chlorotic ring patterns in plum leaves D) Necrotic ring patterns on apricot Western Plant Diagnostic Network News fruit. Plant Virus Vectors 6 The three forms of viruses.