Communicable Plant Diseases and Plant Health Part I
Communicable Plant Diseases and Plant Health – Part I A comparison with human disease; what causes plant disease; some examples; historical context; control Resources to support GCSE and A-level curricula by the British Society for Plant Pathology
1 3 Plant Diseases: damaging & deadly 2 4
Humans get sick. Diseases are caused by microorganisms • Bacteria • Fungi • Viruses
Human pathogens (1) - bacteria Bacterial meningitis symptoms, caused by several different types of bacteria including species of Streptococcus, Neisseria meningitidis, Haemophilus influenzae and Listeria monocytogenes(1) Scanning Electron Micrograph of Mycobacterium tuberculosis the causal agent on Tuberculosis or TB (2)
Human pathogens (2) - fungi Athletes Foot symptoms caused by the fungi Trichophyton spp. (3) Symptoms of ‘thrush’ infection on the tongue, caused by the fungus Candida albicans (4)
Human pathogens (3) - viruses Cut-away model of the HIV-virus the causal agent of human immunodeficiency virus (5). The virus attacks the immune system, and weakens your ability to fight infections and disease. Mainly transmitted through sexual contact Influenza virus particles spread upon sneezing. Salivary droplets being expelled from the man’s open mouth (6)
Plants get sick. Diseases are caused by micro-organisms • Bacteria • Fungi • Viruses
The disease-causing agents that makes plants sick are called plant pathogens • Plant pathogens cause 10 – 30% crop yield losses annually • Most plants are resistant to most pathogens; disease is the exception, not the rule
Plant pathogens (1) - bacteria Ring rot of potato is caused by the bacterium Clavibacter michiganensis subsp. sepedonicus (7) Note pitting and rot of the vascular ring. Crown Gall Disease (8) seen at the base of an oak tree, and caused by the bacterium Agrobacterium tumefaciens. Growths more typically smaller
More bacterial plant pathogens Xylella fastidiosa – pictured on oranges causing Pierces-disease. (9) showing characteristic chlorotic (yellowing) symptoms on the leaves. Xanthomonas oryzae - causing Bacterial Leaf Blight in wheat & rice (10) characterized by chlorotic (yellow) streaking in the leaf, reducing photosynthesis
Plant pathogens (2) - fungi Black Sigatoka symptoms in banana caused by the fungus Pseudocerospora fijiensis (11) Chlorotic streaks merging into one another, eventually giving dead tissue Symptoms of powdery mildew infection on barley, caused by the fungus Blumeria graminis (formerly Erysiphe graminis) (12)
More fungal plant pathogens Black leaf spot in rose caused by the fungus Diplocarpon rosae (13) Entire leaves turn yellow in addition to the black spots. Ash Dieback - caused by the fungus Hymenoscyphus fraxineus - affecting Ash Trees (14) causing leaf and branch loss particularly in the crown (above). Fungal fruiting bodies
Plant pathogens (3) - viruses healthy TMV infected Yellowing symptoms of Tobacco Mosaic Virus (TMV) infection in tobacco (15) Stunted growth, leaf curling, rolling and mottling symptoms may also been seen Electron-micrograph of the rods of Tobacco Mosaic Virus (TMV) – scale bar = 100 nm (16)
More viral plant pathogens Barley Yellow Dwarf Virus (BYDV), a viral disease transmitted by aphids. (17) Leaves turned yellow across their entire length, compared with green ‘healthy’ leaves (top) Symptoms of Cassava Brown Streak Disease. An emerging disease of increasing importance transmitted by whiteflies and caused by 2 related viruses. (18) Necrotic (brown) decaying tissue throughout the tuber making it inedible
Fungi, bacteria & viruses cause disease in humans & plants Fungi (eukaryotes) Bacteria (prokaryotes) Virus (non-cellular, packaged nucleic acid)
Some plant pathogens belong to the Kingdom Protoctista (Protists) • Protists are eukaryotes. They’re not plants, animals or fungi. Protists fall into four general subgroups: unicellular algae, protozoa, slime moulds, and water moulds. They include 2 major disease causing organisms of humans and plants • Plasmodium spp. , the malaria parasite, carried by mosquitoes • Phytophthora infestans (an oomycete), the causal agent of Potato Late Blight which devastated the potato crop during the Irish Potato Famine (1845)
Plasmodium vivax parasitising blood cells
Phytophthora infestans
For as long as people have grown crops they have battled with their diseases
Diseases were often blamed on the gods Once it was thought that gods and goddesses controlled natural events. The Greek goddess of the harvest was Demeter, while the Roman equivalent was Ceres or Demeter was the goddess of grain Demeter (19) Ceres (20)
“Robigalia” – to save the crops • A Roman Festival for the god, Robigus, held on the 25 th April • Roman’s believed Robigus would prevent crop disease if they made sacrifices in his honour • The main ritual was a dog sacrifice to protect the grain fields from wheat rust, a fungal disease with a reddish/brown coloured spores. • The dogs would usually have a red coats
‘Robigus’ protected against this fungus – wheat stem rust, still a major problem
Its not just the disease … • As well as crop yield losses, some fungal infections are accompanied by toxin production, secondary metabolites produced by the fungus during its normal growth or when put under stress (mycotoxins) • These mycotoxins, if consumed, can be deadly to both humans and livestock. • If not deadly, they often give dramatic symptoms …
The consumption of rye grains reported to cause: Burning and convulsions Hallucinations with imaginary sounds Gangrene and loss of limbs Permanent insanity • Initial burning sensation led to Latin name, Ignis sacer meaning holy fire. • A religious order dedicated to St. Anthony was founded in 1083 to help the afflicted. The condition became known as St. Anthony’s fire
St. Anthony’s Fire • In 1670, a French physician concluded ergotism was not an infectious disease and attributed it to food. Despite his suggestion of a link to rye ergots, farmers did not believe him. The link with the fungus causing ergots in rye (Claviceps purpurea) took another 200 years to be made. • Developing grains in the ear replaced with Ergots which are sclerotia (fungal overwintering survival structures) • Ergots contain several alkaloids. Some are potent vasoconstrictors (e. g. ergotamine) while others are psychoactive (LSD, lysergic acid diethylamide). • Ergotism takes 2 forms – gangrenous / convulsive – both fatal • Spores released from sclerotia Ergots – long, black infect cereals at flowering, structures among healthy grain completing the cycle.
Ergotism & Witchcraft • 990 – 1129 AD, ergotism believed to have killed 50, 000 people in South of France • 1692 – convulsive ergotism may have caused symptoms that led to the Salem Witch Trials (USA) in which 20 people were executed • 1926 – 11, 000 victims in USSR • 1927 - Manchester, UK >200 cases • 1951 - French Epidemic, approx. 150 cases • 1970’s to present – outbreaks in India & Ethiopia
Potato Blighted potato leaves caused by the oomycete Phytophthora infestans (21) Infection will spread rapidly through the entire plant Dublin memorial to the 1. 5 million killed by starvation during the Irish Potato Famine, 1845 -52 (22)
Impact of Blight on Irish population Phytophthora infestans was introduced to Ireland from South America (where the potato originates) Population Cool, wet summers provided ideal conditions for the fungus to flourish Irish labourer ate ~5. 4 kg potatoes a day spread across 3 meals Many emigrated to the United States to flee from the famine Population yet to recover Blight outbreak
Brief History of Plant Disease 1863 Anton de Bary shows potato blight caused by Phytophthora Germ Theory Louis Pasteur (1881) T. J. Burrill (1878) demonstrated that fire blight of pear and apple was caused by a bacterium, Erwinia amylovora 1890 TMV shown to be caused by a virus (1898) By the end of the 19 th century, pathologists knew why plants got sick
Research in the 20 th century focused on the prevention and control of disease outbreaks 1. Chemical Control 2. Cultural Control 3. Genetic Control
Chemical Warfare ! Many plant diseases are controlled by spraying regularly during the growing season with chemicals Issues: - Pathogens can evolve resistance to the chemicals; environmental concerns about spraying limits
Cultural Control – inc. ‘ploughing-in’ Many plant diseases can persist in the soil or on ‘stubble’ from one season to another Burning crop residues / stubble burning effectively banned in UK since 1993 (due to pollution fears). ‘Ploughing-in’ encouraged.
Genetics of Disease Resistance Resistant Susceptible Plant Breeders try to introduce disease resistance genes into susceptible varieties but it’s a complex trait. It can take 7 years or more to breed a new variety but can be very effective.
The Role of Plant Breeders How do we create a high-yielding bread wheat, less likely to suffer from disease? Variety A Yield HIGH Disease LOW Resistance Crosstogether X Variety B Yield LOW Disease HIGH Resistance Select for progeny, plants which are HIGH yielding and have HIGH Disease Resisatnce
The Disease triangle ge Pa tho The disease triangle (it takes three) Environment st Ho The pathogen must be able to overcome plant defences n Plants are exposed to countless microbes, but very, very few of these interactions lead to disease. Why? The host plant must be susceptible to the pathogen The environment must tip the balance in favour of the pathogen
Humans influence diseases 1. Migrations of people and plants Humans add another dimension (making a disease pyramid…. ) 2. Monoculture ma Hu ns 3. Introduced pathogens and vectors Envi ronm Ho st Pathogen ent 4. Growing practices
The environment affects whether the plant or pathogen wins – many factors Temperature Rain Wind Planting density Pollution Other organisms Moisture content Nutrient availability
ge Pa tho The disease triangle (it takes three) Environment st Ho Avoid or eliminate the pathogen n Human strategies to prevent and manage disease Make the plant resistant through genetic or other methods Manipulate the environment to favour the plant
More about host: pathogen interactions in Part II
Acknowledgements (1 of 2) • The BSPP gratefully acknowledges the ASPB for granting access to its Teaching Tools in Plant Biology series. The presentation “Fighting for their lives: plants and pathogens” helped frame this presentation and some slides have been used directly with the editors permission. Herman, M. , and Williams, M. E. (June 27, 2012). Fighting for their lives: Plants and pathogens. Teaching Tools in Plant Biology: Lecture Notes. The Plant Cell (online), doi/10. 1105/tpc. 112. tt 0612. • For more excellent plant biology teaching resources go to their website, http: //www. plantcell. org/site/teachingtools/ • This presentation is prepared under a Creative Commons License, Attribution-Non. Commercial-Share. Alike 4. 0 International (CC BY-NC-SA • Additional images have been sourced as follows. All are within the public domain or used with the authors permission. • Slide 2. Photos courtesy of (1) Fusarium on Maize c/o CIMMYT, (2) Blighted Potato: c/o Prof. Louise Cooke, Queens University Belfast (3) Bleeding Cankers on mature European Beech Trees caused by Phytophthora cambivora; c/o Dr. Richard O’Hanlon, Department of Agriculture, Food and the Marine, Ireland (4) Botrytis cinerea on grapevine c/o Prof. Chris Steel, National Wine & Grape Industry Centre, Wagga, NSW, Austrailia Slide 4. (1) – Wellcome Photo Library, Wellcome Images, N 0000730 (2) - Janice Carr: CDC/ Dr. Ray Butler; Janice Carr - This media comes from the Centre for Disease control and Prevention’s Pubic Health Library id no. #8438 Slide 5. (3) - Wes Washinton, Wikipedia Creative Commons (4) - Credit Wellcome Images, Wellcome Images Candida albicans, - 0018418 Slide 6. (5) John Wildgoose, Wellcome Images Cut-away model of HIV; (6) James Gathany - CDC Public Health Image library ID 11162 Slide 9. (7) Ring Rot, potatoes: FERA Crown Copyright (8) Crown Gall Disease : Dr. Daniel Pacurar, Umeå University, Sweden. Image first appeared in Physiological & Molecular Plant Pathology (Vol. 76, 2011) Slide 10. (9) Alexander Purcell, University of California, Bugwood. org - - http: //www. invasive. org/browse/detail. cfm? imgnum=1262027 (10 Donald Groth - http: //www. ipmimages. org/browse/detail. cfm? imgnum=5390469, CC BY 3. 0, https: //en. wikipedia. org/w/index. php? curid=44597430 Slide 11. (11) Black Sigatoka: Prof. Gert Kema, Wageningen University, The Netherlands (12) Powdery Mildew: Dr. Phil Smith, John Innes centre, Norwich Slide 12 (13) Rose Black Spot: Image copyright, Royal Horticultural Society (14) Ash. Dieback: Image copyright Prof. James Brown & Dr. Elizabeth Orton, John Innes Centre, Norwich Slide 13 (15) Dr. John P. Carr, Department of Plant Sciences, University of Cambridge (16) Prof. Roger Hull (Emeritus Professor, John Innes Centre, Norwich) taken from Hull (2009), Comparative Plant Virology 2 nd edition Slide 14 (17) Keith Weller Agricultural Research Service, Wikimedia Commons (18) International Institute of Tropical Agriculture (Flickr), Slide 17. Plasmodium CDC/Mae Melvin, by CDC/Dr. Mae Melvin http: //phil. cdc. gov/phil_images/20021230/12/PHIL_2720_lores. jpg. Mosquito: Wellcome Images • • • 4. 0), https: //creativecommons. org/licenses/by-nc-sa/4. 0/
Acknowledgements (2 of 2) • • • • • Slide 18 Phytophthora infestans: Prof. Louise Cooke, Department of Agriculture, Northern Ireland Slide 19 Photographic reproduction of a two-dimensional work of art in the public domain – ‘Pintura del Antiguo Egipto mostrando la trilla del trigo’ Wikipedia Slide 20 Bible Image, CC 0 Public Domain, http: //maxpixel. freegreatpicture. com/Religion-Bible-Books-Bible-Study-Christian-501969 Slide 21 (19) Neustrelitz-goetter 2 -demeter by user Ruchhöft-Plau, class="int-own-work”. Licensed under Public Domain via Wikimedia Commons (20) Ceres - Dominikus Auliczek um 1770 -1. jpg. Nymphenburger Porzellanmanufaktur, Porzellanmuseum München Slide 23 Stem Rust on wheat courtesy of Prof. Zacharias A. Pretorius, University of the Free State, South Africa. Slide 25 A section of the Isenheimer Altar painted by Mathis Grünewald believed to personify a disease caused by ergot poisoning, resulting in swelling and ulcerous growths. Mathis Gothart Grünewald 018 - The Yorck Project: 10. 000 Meisterwerke der Malerei. DVD-ROM, 2002. <a href="//commons. wikimedia. org/wiki/Special: Book. Sources/3936122202" class="internal mw-magiclink-isbn">ISBN 3936122202</a>. Distributed by DIRECTMEDIA Publishing Gmb. H. . Licensed under Public Domain via wikimedia Commons Slide 26 File: Hordeum vulgare Claviceps purpurea 23 -7 -2009. JPG From Wikimedia Commons. Image by Dominique Jacquin. Slide 27 (21) Blighted Potatoes: Prof. Louise Cooke (22) Famine Memorial Dublin: by Alan. Mc (2006) from en. wikipedia Slide 29 Population of the island of Ireland since 1600. The original uploader was Rannpháirtí anaithnid (old) at English Wikipedia - transferred from en. wikipedia to Commons by Andreasmperu using Commons. Helper Slide 31 Miniature reproductions of the images on the next 3 slides (Nos. 32, 33, 34) Slide 32 https: //pixabay. com/en/tractor-spraying-crop-spraying-164360/ Slide 33 Photo courtesy of Ryetech, http: //www. ryetec. net/ Slide 34 Photo courtesy of Dr. Phil Smith, John Innes Centre, Norwich Slide 35 Wheat variety trial at Gypsy Corner Farm © Copyright Michael Trolove and licensed for reuse under this Creative Commons Licence Slide 37 - ASPB Photos courtesy Scott Bauer and Bob Nichols, USDA, and Geovantage, Inc Slide 38– ASPB Photo by Jack Dykinga / Fred Brooks, University of Hawaii at Manoa; Linda Haugen, USDA Forest Service, Bugwood. org. Slide 40 Photo courtesy of Dr. Diane Saunders, John Innes Centre and Earlham Institute, Norwich
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