BIOL 3025 Molecular Plant Pathology Lecture 1-Introduction PDF

BIOL 3025: Molecular Plant Pathology: Lecture 1- Introduction Dr. ANGELA. T ALLEYNE 1  At the end of this lecture you should be able to: ✓ Explain the term “plant disease”...

BIOL 3025: Molecular Plant Pathology: Lecture 1- Introduction Dr. ANGELA. T ALLEYNE 1  At the end of this lecture you should be able to: ✓ Explain the term “plant disease” ✓ Describe pathogen types LEARNING OUTCOMES ✓ Explain the disease triangle. ✓ Explain Koch's Postulates ✓ Differentiate between a disease sign and symptom ✓ Describe common plant disease symptoms 2  Plant Pathology 1845-1851- widespread Infectious spontaneous The great studies on “ microbes generation Irish potato the stinking were of microbes Famine and mass of discovered displaced by the birth of rotten to be the the accepted plant potatoes” in reason for germ theory pathology Europe the of disease. destruction 3 http://www.smithsonianmag.com/science-nature/scientists-finally-pinpoint-the- pathogen-that-caused-the-irish-potato-famine-71084770/?no-ist of potatoes  http://www.smithsonianmag.com/science- nature/scientists-finally-pinpoint-the-pathogen- that-caused-the-irish-potato-famine- 71084770/?no-ist http://www.apsnet.org/edcenter/intropp/HungryPlanet/Chapter1/Pages/ImageGallery.aspx Irish Potato Famine  Microbial phytopathogens Image produced by Marcia P. McMullen and H. Arthur Lamey (2001) 5  Xanthomonas campestris Microbial phytopathogens Xanthomonas Streptomyces Ralstonia Xylella Agrobacterium Pseudomonas Clavibacter Phytoplasmas 6  Recall: Prokaryotic cells cell wall peptidoglycan – Gram pos. & Gram neg Image courtesy: http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/Bacteria.aspx 7  Fungal phytopathogens Colletotrichum Cercospora Ustilago Puccinia Phytophthora Erysiphe Claviceps Fusarium Colletotrichum species 8 Fungi Image courtesy : http://www.cliffsnotes.com/assets/8371.jpg 9  Viruses 1. Tobacco mosaic virus (TMV), 2. Tomato spotted wilt virus (TSWV), 3. Tomato yellow leaf curl virus (TYLCV), 4. Cucumber mosaic virus (CMV), 5. Potato virus Y (PVY), 6. Cauliflower mosaic virus (CaMV) 7. African cassava mosaic virus (ACMV), 8. Plum pox virus (PPV), 9. Brome mosaic virus (BMV) and 10. Potato virus X (PVX). http://link.springer.com/article/10.1007%2Fs00705-014-2295-9 10  RNA, DNA typical diameter ~30 nm (plant virus) ss, ds Virus Nucleic acid structure + protein + sense, - multipartite sense genome segmented genome spherical Rod Images courtesy: http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx Some Common Plant Pathology Terms Biotroph Resistance Necrotroph Pathogen Hemibiotroph Host-defense Host & non-host Pathogenicity Virulence 12  Disease –abnormal physiological or Pathogenesis developmental change in a host due to the persistent action of a biotic or abiotic factor: Detrimental to hosts Disease triangle 13  “A disease is the result of a dynamic, detrimental Definition relationship between an organism that parasitizes or of disease interferes with the normal processes of cells or tissue, or both, of the plant. The organism that incites or causes the disease process with the host is called a pathogen. … Plant stresses or plant injuries are not diseases because they are not dynamic; that is, they do not change over time.” 14 Windham & Windham Definition of disease “Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogenic agent or 15 environmental factor and leads to development of symptoms.” Agrios Pathogen 1960 1998 2005 both animate an organism, transmissible and often a biotic agents inanimate micro- that can pathogens: organism, a cause disease Horsfall & virus or Dimond viroid, which causes disease 16 Pathogenicity The pathogen either does or does not cause a disease. Pathogens are either: virulent or avirulent 17 Virulence Relative capacity of pathogen to cause disease; ranges from minimal damage to dead plant. 18 Etiology Determining the cause of disease 19 Epidemiology Study of the factors influencing the initiation, development and spread of infectious disease 20  ABIOTIC BIOTIC Light Animals (including humans) Biotic & Temperature Plants Abiotic factors Water Insects Soil factors Chemicals Microbes Nutrients Benign Pesticides Beneficial Natural Pathogens Organics 21  Disease Environmental conditions influence each and every step in disease development process  2 3 Disease Triangle Concept was first published by Stevens in 1960 Disease management considers the disease triangle A plant disease is prevented upon elimination of any one of these three causal components Image Courtesy: http://www.apsnet.org/publicati ons/apsnetfeatures/Publishing Images/1998%20Features/Ma rch/1-18.JPG  A CRITICAL ASPECT DISEASE ONSET AND SYMPTOMS AND Time: OF INTENSITY ARE SIGNS CAN TAKE a consideration EPIDEMIOLOGICAL AFFECTED BY THE LONG TO APPEAR EVENTS OR OF DURATION THAT BUT DISEASE SEVERITY THE THREE FACTORS PHYSIOLOGICAL IN A POPULATION IS ARE ALIGNED. EVENTS OR TIME INFECTION USUALLY TAKE MINUTES TO HOURS. 24 The Disease doughnut Pathobiome- new concept of disease Pathobiome- the disease-assisting portion in the plant microbiome, Pathobiome- host pathogenesis-associated microbial consortia. Pathobiome- some native members in the resident microbiota can also be potential pathogens and an accumulation or change in the relative abundance of these members in their hosts can lead to disease onset or greater severity 26 Pathobiome- new concept of disease Microbial eukaryotic, communities. microbial, and viral a complex of communities within bacterial or fungal the plant’s biotic Pathobiome environment which species are involved in the disease Network of host interact with the process and microbe host plant to deteriorate its health interactions 28 https://doi.org/10.3390/plants10010125 Koch’s postulates (1890) To prove that an organism causes a disease 1 Frequent Isolation from association with symptomatic disease tissue 4 2 Re-isolation of Inoculation of same organism healthy tissue from results in symptomatic development of tissue 3 same symptoms 29  Microbes that are Symptoms/diseases difficult to culture in may be caused by Some pathogens may vitro (use DNA more than one cause several diseases evidence) organism Some Koch exceptions Fredericks and Relman (1998) The copy number (count) of the A nucleic acid sequence pathogen-associated nucleic acid (DNA/RNA) of known pathogen sequences should decrease or should be found associated with a become undetectable in case of disease, found symptoms sites. resolution of disease. The relationship between the sequence and tissue should be tried to establish at the The nature of the microorganism cellular level; to demonstrate the inferred from the available hybridization of the microbial sequence to sequence should be consistent the areas of tissue pathology and to visible with the known biological microorganisms or to areas where microorganism are thought to be involved. characteristics of that group. Sequence based forms of evidence should be reproducible. 31  Symptoms - the visible response of a –Localized plant to the vs. systemic aetiological agent Signs – micro- or macroscopic structures the living agent. produced by Signs & Symptoms – more specific than symptoms – more useful in accurate disease diagnosis 32  Common signs of plant disease Exudates or ooze- Mildew- Mycelia Mould- Fungal Rust- Rust spores Bacteria oozing (cottony growth) mycelia or visible on leaf from leaf structures 34 Change in Examples of Mosaic, Leaf spot, Leaf Hypoplasia & Blight – spots normal symptoms Chlorosis, Rot, curl hyperplasia, that have appearance Wilt Hypertrophy, coalesced or Stunting merged together Necrosis or death of parts of plant Underdeveloped tissues or Organs Overdeveloped tissues or organs Symptoms of plant disease  blight mosaic rot cankers wilt 36  Target spot lesion on tobacco caused by Rhizoctonia solani http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig06.htm Bacterial leaf spot on greenleaf lettuce caused by Xanthomonas campestris pv.vitians http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig07.htm  Mosaic on leaves of squash http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig09.htm Peanut leaf with concentric ring spots caused by Tomato spotted wilt virus (TSWV). http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig10.htm Powdery mildew on apple blossom cluster caused by Podosphaera leucotricha http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig05.htm Stem rust on barley, caused by Puccinia graminis. http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig04.htm  Herbicide injury of beans http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig14.htm  Canker on apple caused by Nectria galligena http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig17.htm  Brown rot of peach caused by Monilinia fructicola http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig18.htm  Verticillium wilt of cucumber caused by Verticillium dahliae. http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig21.htm  Brown rot of lettuce caused by Botrytis cinerea 47 Crown gall on Euonymous caused by Agrobacterium tumefaciens. http://www.apsnet.org/education/introplantpath/Topics/plantdisease/text/fig26.htm  REFERENCES Agrios, G.N. 2005. Plant Pathology (5th edition). ElsevierAcademic Press, San Diego, CA Trigiano, R. N., Windham, M. T., and Windham, A. S. (2008) Plant Pathology: concepts and laboratory exercises 2nd ed. CRC Press NY Mannaa, Mohamed, and Young-Su Seo. 2021. "Plants under the Attack of Allies: Moving towards the Plant Pathobiome Paradigm" Plants 10, no. 1: 125. https://doi.org/10.3390/plants10010125 49