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Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Diseases Caused by Bacteria and Mollicutes Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Important Characteristics Bacteria Prokaryote Genetic material (DNA) not bound by a membrane (lack nucleus) Cytoplasm surrounded by a cell membrane & a cell wall Lack organelles such as mitochondria and chloroplasts Cells consist of cytoplasm containing DNA & small (70 S) ribosomes Mollicutes Similar to bacteria except lack of a cell wall In the past known as mycoplasma-likeorganism (MLO) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Important Characteristics (cont’) Plant pathogenic bacteria Plant pathogenic phytoplasmas Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Morphology of Bacteria 1. 2. 3. 4. Coccus Rod Spiral Filamentous (branched mycelium) Source: JPT 1 2 3 Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria: Morphology Most species are rod shaped, except Streptomyces (filamentous) 1.0-5.0 (L) x 0.5-1.0 (W) µm Cell walls of most species are enveloped by a gummy material Most species have flagella: polar flagella: one or many at one end of the cell, e.g., Pseudomonas, Xanthomonas peritrichous flagella: one or many distributed all over, e.g., Agrobacterium, Erwinia Agrobacterium Pseudomonas Erwinia Xanthomonas Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria: Morphology Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria: Morphology (cont’) Colony: different according to species Shape: circular, oval, irregular Edge: smooth, wavy, angular Elevation: flat, raised, wrinkled Color: whitish, grayish, yellow Some produce fluorescent pigment under UV light Example: Colonies of Xanthomonas producing xanthomonadin Genus Xanthomonas produces yellow pigment called xanthomonadin Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria: Morphology (cont’) Pigment production Pseudomonas: fluorescent Erwinia: zeaxanthine (cream), rubrifacin Xanthomonas: xanthomonadins (yellow) Clavibacter: carotenoids (yellow) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Gram Stain Developed by a Danish doctor, Hans Christian Gram in 1884 Gram reaction: Based on structure of bacterial cell wall Divide bacteria into 2 groups: 1. Gram positive: stained purple due to peptidoglycan layer 2. Gram negative: stained pink due to an additional outer membrane (stain unable to reach peptidoglycan layer Gram stain procedure: crystal violet + iodine + alcohol + safranin Non-staining test: 3% KOH Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Mollicutes: Morphology Divided into 2 groups: 1. 2. Phytoplasmas Spiroplasmas Lack flagella and spores Gram negative Shape: spherical, ovoid, filamentous, helical Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Mollicutes: Morphology (cont’) 1. Phytoplasmas 2. Spherical, ovoid, filamentous Diameter: 0.3-2 µm Spiroplasmas Phytoplasmas Helical Diameter: 0.12 µm Length: 2-4 µm Spiroplasmas Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria and Mollicutes: Ecology Parasites (live in host plants) Saprophytes (live in plant debris or soil) Bacteria: Most species: facultative saprophytes, can be grown artificially on nutrient media Fastidious vascular bacteria: difficult to grow in culture Nutrient intake: diffusion E.g. of artificial nutrient medium: nutrient agar (NA), pH ~7.0 Mollicutes: Phytoplasmas: cannot be grown on artificial nutrient media & disease yet to be reproduced Spiroplasmas: can be grown on artificial nutrient media & disease can be reproduced Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Classification of Plant Pathogenic Bacteria ≈ 1,600 species are known ≈ 100 species cause diseases in plants References: International Code of Nomenclature of Bacteria (revised 1976) Labotatory Guide for Identification of Plant Pathogenic Bacteria (American Phytopathological Society, 2001) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Classification of Plant Pathogenic Bacteria (cont’) Classification based on: Gram stain Morphology Biochemical requirements Classification not stable Pathovars (1980) Subspecies Biovars Serovars Phagovars Example: Xanthomonas axonopodis (campestris) pv citri (citrus canker bacterium) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Classification of Plant Pathogenic Bacteria (cont’) Kingdom Division Prokaryote Gracilicutes Class Attribute Proteo- Gram bacteria negative bacteria Family Enterobacteriaceae Pseudomonadaceae Rhizobiaceae Undefined Firmicutes FirmiGram bacteria positive bacteria Thallo- Gram bacteria positive branching bacteria Genus Erwinia Pseudomonas Ralstonia Xanthomonas Agrobacterium Xylella Bacillus Clostridium Streptomyces Clavibacter Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Classification of Plant Pathogenic Mollicutes Kingdom Division Prokaryote Tenericutes Class Mollicutes Attribute Family Genus Wall-free prokaryotes Spiroplasmataceae Spiroplasma Undefined Phytoplasma Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria and Mollicutes: Reproduction Asexual reproduction: binary fission (rodshaped bacteria & mollicutes) Reproduce at an extremely rapid rate: divide every 20-50 min 1 bacterium could produce 106 progeny in < a day Extremely large populations cause: great chemical changes in their environment development of bacterial diseases in plants Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Plant Pathogenic Bacteria and Mollicutes: Reproduction (cont’) Stationary phase No. of cells Death phase Lag phase Exponential phase Time Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Infection Process The process involved 3 steps: Penetration 1. 2. Invasion 3. Colonization Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Infection Process (cont’) Penetration 1. Through stoma, wound, hydathode, nectarthode Bacteria surrounding a stoma of host plant Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Infection Process (cont’) Invasion 2. Pathogens invade intra- and intercellular tissues Example: Vascular wilt bacterium invade xylem tissues Colonization 3. Pathogens reproduce at a rapid rate Progeny carried passively into new cells through xylem & phloem Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. History 1876 R. Koch: First bacterium discovered to infect animals & humans, anthrax by Bacillus anthracis 1878 T.J. Burill: Fire blight bacterium discovered in pear & apple trees 1901 E.F. Smith: Bacteria was proven to cause plant diseases 1967 Y. Doi et al.: Discovery of Mycoplasma-likeorganisms (MLO) in Japan 1972 Windsor & Black: Studied epidemic of Pierce disease of grapes caused by fastidious phloemor xylem-inhabiting bacteria Davis: Discovery of spiroplasma Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Importance of Plant Pathogenic Bacteria and Mollicutes Cause tremendous economic losses Direct: lower yield & quality of plant products Indirect: increase costs - chemicals, resistant varieties, management Examples: Soybean blight: losses of US$65 mil/year Crown gall of fruits and nuts: losses of US$23 mil/year Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria and Mollicutes Bacteria Citrus canker 1. Bacterial leaf blight 2. Bacterial wilt 3. 4. Soft rot 5. Crown gall Citrus greening 6. Mollicutes 1. Lethal yellowing 2. Citrus stubborn Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria 1. Citrus Canker Pathogen: Xanthomonas axonopodis (campestris) pv citri Host: Citrus Distribution: Citrus growing areas Symptom: sunken spots surrounded by yellow halo on leaves, branches & fruits Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria (cont’) Bacterial Leaf Blight 2. Pathogen: Xanthomonas oryzae pv. oryzae Host: Rice Distribution : Worldwide Symptoms: Necrosis on sides of leaf blades Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria (cont’) 3. (Southern) Bacterial Wilt Pathogen: Ralstonia (Pseudomonas) solanacearum Hosts: Solanaceous plants Distribution: Places with warm climates Symptom: Sudden wilt, brown discoloration in vascular tissues Host: Tomato Host: Potato Brown discoloration in xylem Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria (cont’) 4. Soft Rot Pathogen: Erwinia caratovora Hosts: Fruits, vegetables, ornamentals Distribution: Worldwide Symptom: watersoaked lesions, disintegration of tissues, foul odor, infecting fleshy storage tissues & aided by insects Host: Carrot Host: Celery Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Bacteria (cont’) 5. Crown Gall Pathogen: Agrobacterium tumefaciens Hosts: Woody & herbaceous plants Distribution: Worldwide Symptoms: Development of tumors or galls of various sizes & shapes at lower stems & main roots Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Phloem-Inhabiting Fastidious Bacteria 6. Citrus Greening Disease Pathogen: Candidatus liberobacter asiaticus (Asia), C. liberobacter africanus (Africa) Host: Citrus Distribution: Asia & Africa Symptom: Yellowing leaves & stunted growth, lopsided fruits & fail to ripe (green) Dissemination: Vegetative reproduction & psyllid insects Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Mollicutes (cont’) 1. Lethal Yellowing Pathogen: Phytoplasma Host: Coconut Distribution: USA, Mexico, West Africa, etc. Symptoms: Pre-mature drop of coconuts, blackened tips in flowers, fronds turn yellow, die & drop, leaving only trunk Phytoplasmas passing through a sieve-plate pore. Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Diseases Caused by Plant Pathogenic Mollicutes (cont’) 2. Citrus Stubborn Pathogen: Spiroplasma citri Host: Citrus Distribution: Hot & dry areas Symptoms: Stunted growth, bunchy shoots, mottled or chlorotic leaves, very small & lopsided fruits Dissemination: Budding & grafting, leafhoppers Source: Agrios (2005) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Thank You Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Quiz 1. What is the morphological difference between bacteria and mollicutes? What is the colour of the pigment that Xanthomonas produces? What is the name of the staining procedure that is used for bacterial classification? Name two types of Mollicutes What is the causal agent of Citrus canker (genus name) and Lethal yellowing of palms?