Published on February 13, 2008
Bacteria as Plant Pathogens III: Gram Positive and Fastidious Bacteria (Phloem-limited, Cell Wall –Free): Bacteria as Plant Pathogens III: Gram Positive and Fastidious Bacteria (Phloem-limited, Cell Wall –Free) Plant Pathology 415 Fall 2006 Lesson 23 Gram Positive Plant Pathogens: Gram Positive Plant Pathogens Bacillus – Gram variable, large, motile, facultatively anaerobic rods that produce endospores. Clostridium – Spore forming anaerobic rods that can be Gram variable, found in soil and decaying plant material. Coryneform group – Gram positive (may decolorize easily), pleomorphic rods, aerobic, snapping division. Arthrobacter Clavibacter Curtobacterium Rathayibacter Rhodococcus Actinomycetes – filamentous growth. Streptomyces Gram Positive Classification: Gram Positive Classification Bacillus species: Bacillus species Bacillus are Gram variable, endospore producing, aerobic and anaerobic, motile rods, some species have filamentous growth. Bacillus species can be saprophytic, plant pathogenic, act as biological control agents or plant growth promoters. There are single published reports of: Bacillus megaterium pv. cerealis – white blotch of wheat. Bacillus circulans – seedling death and heart discoloration of date palm. Bacillus polymyxa – tomato seedling blight. Bacillus subtilis – soybean seed decay. Bacillus species: Bacillus species Probably the most famous or infamous member of this group is Bacillus anthracis, the causal agent of anthrax in animals (not a plant pathogen). The bacterium is encapsulated, spore-forming, rod shaped, zoonotic. Commonly occurs in wild and domestic vertebrates (cattle, sheep, goats, and other herbivores). Good Bacillus species: Good Bacillus species Bacillus subtilis – certain strains suppresses Rhizoctonia spp. Seedling disease of peas. Summer patch in Kentucky Bluegrass. Bacillus thuringiensis Clostridium: Clostridium Anaerobic, spore-forming rod-shaped, pectolytic bacteria. Frequently found in decaying plant material, soil. “Wetwood” diseases Tepa wood – butterfly stain Populus spp – C. butyricum. Most famous C. botulinum C. tetani Clostridium: Clostridium Anaerobic, spore-forming, pleomorphic cells that are fond of soil, often with a bulge at the end. Clostridium tetani from Dr. Glen Stronger, http://www.microvet.arizona.edu/Courses/mic420/lecture_notes/clostridia/clostridia_neurotox/c_tetani.html Clostridium botulinum: Clostridium botulinum Spores are everywhere (soil and marine sediments, surfaces of fruits and vegetables, and in seafood). Bacteria and spores are harmless; the dangerous substance is the neurotoxin (A through G). Absence of oxygen, low acidity levels, and temperatures between 40 and 120 degrees F (4.5 to 49 C). Botulism: Botulism Three types Infant Wound Food-borne Symptoms Early signs consist of marked lassitude, weakness and vertigo, usually followed by double vision and progressive difficulty in speaking and swallowing. Difficulty in breathing, weakness of other muscles, abdominal distention, and constipation may also be common symptoms. The Coryneform Group: The Coryneform Group A diverse group of pleomorphic rod-shaped bacteria, snapping division, strict aerobes. Gram positive although they may decolorize rapidly. Vascular pathogens, hence many are seedborne. Gram stain of Clavibacter michiganensis subsp. michiganensis. The Coryneform Group: The Coryneform Group Common symptoms produced by members of this group are galls, gummosis, stunting, fasciations, and wilts. Major Genera Arthrobacter Clavibacter michiganensis rathayi tritici toxicus xyli Curtobacterium Rhodococcus Clavibacter michiganensis subspecies insidiosus – Alfalfa Wilt: Clavibacter michiganensis subspecies insidiosus – Alfalfa Wilt Infected plants are scattered randomly in the field, wilt under moisture stress. From a distance, will appear yellow and slightly dwarfed. Usually do not grow well after the first cutting. Stems have gummy pockets and roots are yellow to brown. Bacterial Wilt of Alfalfa: Bacterial Wilt of Alfalfa michiganensis subsp. insidiosus Survival: plant material in soil, hay, and seed (years). Spread: surface water, contaminated tools, contaminated hay and seed (long distance). Common in low, poorly drained areas, wet years. Nematode (Meloidogyne hapla, Ditylenchus dipsaci) feeding, winter injury, mechanical injury aids root infection. Pathogenesis: colonizes vascular system and disrupts water transport (occlusion) and by a phytotoxic glycopeptide. Clavibacter: Clavibacter michiganensis subsp. michiganensis Grand Rapids disease, bird’s eye spot, bacterial canker of tomato. Bacterial Canker of Tomatoes: Bacterial Canker of Tomatoes michiganensis subsp. michiganensis. Survival: Infected seed and transplants are the main sources of inoculum. However, seed tests are not 100% guaranteed to prevent introduction. Not an efficient soil survivor. Will survive indefinitely in plant debris. 10 months dried on plant stakes. Spread Systemic pathogen. Spread by rain/irrigation splashing, vine training. Clavibacter: Clavibacter michiganensis subsp. sepedonicus. Ring rot of potato, wilt and tuber rot of potato. Highly infectious, zero tolerance in potato seed production areas. One infected seed piece can be spread to 100 seed pieces cut with a contaminated knife. Ring rot of Potatoes: Ring rot of Potatoes Survival and spread. Cut seed, dried slime on inanimate objects (sacks, machinery, sorters, grading equipment, bins, crates, etc.). First reported in Germany. Occurs in North America, South America, Europe. Some evidence of spread by irrigation water and by insects. Streptomyces: Streptomyces Gram positive, filamentous bacteria, spore chains formed through fragmentation of aerial hyphae. Can survive as a saprophyte, pass through digestive tracts. Can be disseminated by wind, water, contaminated tools, seed. Not normally a problem, can arise in drier fields, lacking antagonists or new fields. Can infect a number of hosts (rutabagas, beets, parsnips, carrots, radish, turnips). Slide21: Potato Scab. Scab lesions can be raised (as much as 2 mm above surface) or sunken. Few are plant pathogenic of the over 400 species described. S. scabies – common scab of potato. S. acidiscabies – scab of potato. S. ipomea – pox or soil rot of sweet potato. Produces a family of phytotoxins, thaxtomins. Fastidious Phloem-Limited Bacteria: Fastidious Phloem-Limited Bacteria Bacteria that have not been cultured. Also called rickettsia-like organisms (rickettsia-like bacteria), or bacteria-like organisms. Very small bacteria with a Gram negative type wall. Various shapes, spherical, rod-like, spiral, mycelial, or pleomorphic. Obligate intracellular endophytes. Some appear to be limited to specific tissue types. Fastidious Phloem-Limited Bacteria: Fastidious Phloem-Limited Bacteria Symptoms caused by FPLB’s. Leaf and shoot infection: water-soaked lesions that become necrotic and macerated or slimy, mostly on agronomic crops. Cankers: cherry. Galls: hypertrophy of stem and root tissue. Blights: wilted, necrotic leaves. Wetwood (though it may not be a disease and may not be caused by bacteria): slimy flux from branch stubs, cracks, etc. Scorches: leaves yellowed at margin, with dead tips Yellows: witches’ broom; small, malformed, wavy and yellow leaves. Dieback Stunting Wetwood in Trees: Wetwood in Trees Wood in living trees that appears darker in color (watersoaked), has a fermentative odor, is occupied by bacteria (maybe secondary). Conifers (mostly firs and hemlocks). Hardwoods (elms, poplar, birches, oaks). Mutualism? Colonization by these bacteria lowers oxygen content, inhibiting heart rot fungi in mature trees. Wetwood: Wetwood Wetwood signs and symptoms: dried slime (left) and retarded callus formation (right). From: http://www.ext.colostate.edu/pubs/garden/02910.html Slide26: Fastidious Phloem-Limited Bacteria With the exception of the Clover club leaf and yellows of clover bacteria, most of these pathogens are not located in the Western Hemisphere. Slide27: Asian citrus psyllid adult (above) and nymph (below). From: http://creatures.ifas.ufl.edu/citrus/acpsyllid.htm Citrus Decline Citrus greening, Huanglongbing, yellow dragon disease : Citrus greening, Huanglongbing, yellow dragon disease Symptoms of citrus greening on mandarin orange fruit. Photo courtesy T.R. Gottwald and S.M. Garnsey. Symptoms of Citrus Hunglongbing (greening) in Florida . The symptoms are characterized with yellow mottles, and vary from different host plants. A: Sour orange (Citrus aurantium) ; B: Lime ( Citrus aurantifolia) ; D: unknown (Citrus sp.); C, E, and F: Pummelo ( C. maxima) . Image by Xiaoan Sun, Florida DOACS, Division of Plant Industry. Slide29: Cell Wall-Free Bacteria Spiroplasmas and phytoplasmas (formerly mycoplasma-like organisms), are bacteria that lack a true cell wall. Each cell is bounded by a trilaminar membrane 8-10 nm thick. Slide30: Phytoplasmas Pleomorphic, ~ 0.2 µm (200 nm) diameter. Reproduce by fission & budding. Non-spore-forming. Non-motile Located in the phloem. Disseminated by insects & vegetative propagation. Pear decline, Aster yellows, X-disease of peach, Elm phloem necrosis Phytoplasmas: Phytoplasmas Have never been successfully cultured. All belong to a single monophyletic group. Associated with: Yellows type diseases, Little leaf, virescence phyllody, stunting, bunchy top, witch's broom and other proliferative disorders of plants. Transmitted by phloem feeding leafhoppers, grafting, dodder. Not sensitive to penicillin, sensitive to tetracycline. Slide32: Tomato big bud, large buds that appear swollen and fail to develop fruit. Elm yellows, mid to late summer, leaves turn yellow, dry up. Death of tree usually follows. Slide33: Cell Wall-Free Bacteria Spiroplasma citri Spiroplasma – culturable, differentiated on the basis of serology. Spiroplasma: Spiroplasma Leafhopper-Spiroplasma interactions Pathogenic – infects and invades haemocel. Symbiotic – increased resistance of some leafhoppers to cold temperatures by S. kunkelii. Epiphytic – flower surfaces Spiroplasma as a plant pathogen. Citrus stubborn – S. citri: Citrus stubborn – S. citri Lopsided fruits. Small, unproductive trees. Small fruit or absence of fruit. Stunted feathery growth of canopy. Unseasonal flushes. Sweet orange, grapefruit, tangelo. Problem in young orchards. Vector: beet leafhopper. Review Guide: Review Guide What Are Bacteria? Why are They Important? What are the Major Morphological Features of Bacteria? How do They Differ From Other Plant Pathogens? Gram Negative Bacteria. Gram Positive Bacteria. Fastidious Phloem Limited Bacteria. Spiroplasma and Mycoplasma.