Bacteria And Rickettsia PDF

Leila Geagea, PhD 1 CHAPTER IV BACTERIA AND RICKETTSIA Leila Geagea, PhD 2 Generalities  Bacteria Phytopahogenic bacteria are known since 1882. Prokaryotes without nucleus.  genetic material (DNA) is not bound...

Leila Geagea, PhD 1 CHAPTER IV BACTERIA AND RICKETTSIA Leila Geagea, PhD 2 Generalities  Bacteria Phytopahogenic bacteria are known since 1882. Prokaryotes without nucleus.  genetic material (DNA) is not bound by a membrane. Single-celled micro-organisms. Size is around 1 micron. Their cytoplasm is surrounded by a cell membrane and a cell wall. Leila Geagea, PhD 3 Generalities  Rickettsia-like organisms known since 1972 inhabitants of vascular tissues classified under the branch of the bacteria  fastidious phloem- or xylem inhabiting bacteria they cannot be grown on artificial media. Leila Geagea, PhD 4 Importance of bacterial diseases  About 100 species of bacteria cause diseases in plants.  Incidence of bacterial diseases is important because: it affects directly the production it compromises the growth of tree or plant.  Bacterial diseases of plants occur in every place that is reasonably moist or warm.  Under favorable environmental conditions they may be extremely destructive anywhere. Leila Geagea, PhD 5 Characteristics of bacteria  Erwinia rod shaped peritrichous flagella distributed over the entire surface of the cell colony of white color only ones to be facultative anaerobes Symptoms: soft rot, wilting, spots, blight Leila Geagea, PhD 6 Characteristics of bacteria  Pseudomonas curve rod shaped 2 or many polar flagella colony of white color with a fluorescent pigment inhabitants of soils Symptoms: spots, necrosis, blight, wilting, galls Leila Geagea, PhD 7 Characteristics of bacteria  Ralstonia Until very recently classified as Pseudomonas, these resemble the latter in most respects with the important difference that its cells do not produce fluorescent pigments. Leila Geagea, PhD 8 Characteristics of bacteria  Xanthomonas rod shaped one polar flagellum colony of yellow color only found in association with plants or plant materials Symptoms: leaf spots, cutting rot, black venation, bulb rot, canker, blight Leila Geagea, PhD 9 Characteristics of bacteria  Agrobacterium rod shaped one to 4 bipolar flagella colony of white color rhizosphere and soil inhabitants Symptoms: crown galls, hairy roots Leila Geagea, PhD 10 Characteristics of bacteria  Clavibacter rod shaped motile or nonmotile according to the species colony of yellow-orange to pink color Symptoms: fruit spots, ring rot, canker and wilt, fasciation Leila Geagea, PhD 11 Characteristics of bacteria  Streptomyces shape of branched hyphae: pseudo-mycelium colony at first with a rather smooth surface but later with a weft of aerial mycelium soil inhabitants Symptoms: corky pustules, scab Leila Geagea, PhD 12 Characteristics of bacteria  Xyllela rod shaped nonmotile nutritionally fastidious, Xylella require specialized media; their habitat is xylem of plant tissue Symptoms: leaf scorch, defoliation Leila Geagea, PhD 13 Identification  Morphology not always possible as most of bacteria are rod shaped Streptomyces is the only one that can be morphologically identified.  Food Bacteria are also distinguished  by the substances that they can or cannot use for food  and by the kinds of enzymes produced when the bacteria are grown on certain media. Leila Geagea, PhD 14 Identification  Gram’s staining reactions The chemical compositions of certain substances in bacterial cells can be detected with specific staining techniques. Information about the presence or absence of such substances is used for the identification of bacteria. Gram’s staining reaction differentiates bacteria into  gram-positive types  gram-negative types. Leila Geagea, PhD 15 Identification  Pathogenicity Phytopathogenic bacteria are also tested for their pathogenicity on various species and varieties of host plants. This test, for practical purposes, may be sufficient for tentative identification of the bacterium.  Symptomatology Establish the identity of an isolated bacterium begins with observation  of the external symptom  of the easier internal symptoms. Leila Geagea, PhD 16 Identification  Serological methods especially those employing antibodies labeled with a fluorescent compound (immunofluorescent staining), are used for the quick and accurate identification of bacteria.  Selective nutrient media isolation and identification of bacteria obtained from plant tissues or soil. contains nutrients that promote the growth of a particular type of bacterium while at the same time contain substances that inhibit the growth of other types of bacteria. Leila Geagea, PhD 17 Identification  Molecular methods bacteria are detected, identified, and their genetic relatedness measured by comparison of the DNA bands profiles.  Fatty acid profile analysis extraction and comparison of the fatty acids present in the bacterial cell membranes.  Use of bacteriophages viruses of bacteria. Leila Geagea, PhD 18 Reproduction  Fission Bacteria reproduce at an astonishingly rapid rate.  Under favorable conditions, bacteria may divide every 20 to 50 minutes:  one bacterium conceivably could produce one million progeny bacteria in less than a day. Leila Geagea, PhD 19 Ecology and spread  Almost all plant pathogenic bacteria develop mostly in the host plant as parasites on the plant surface, especially buds, as epiphytes in plant debris or in the soil as saprophytes. Leila Geagea, PhD 20 Ecology and spread  Production of population in host plant  some bacteria produce their populations in the plant host;  once in the soil, their numbers decline rapidly and usually do not contribute to the propagation of the disease from season to season; these bacteria lost their ability to survive in the soil. Leila Geagea, PhD 21 Ecology and spread  Production of population in the soil  bacteria build up their populations within the host plants;  these populations only gradually decline when they are released into the soil;  if susceptible hosts are grown in such soil in successive years, sufficiently high numbers of bacteria could be present to cause a net increase of bacterial populations in the soil from season to season. Leila Geagea, PhD 22 Ecology and spread  Dissemination bacteria with flagella move over short distances. water – rain, drainage, irrigation insects animals human rarely dispersed by wind. Leila Geagea, PhD 23 Ecology and spread  Overwintering on debris dead organs in soils inside oozes on / in seed tubers insects wounds truncs buds Leila Geagea, PhD 24 Control of bacterial diseases of plants  Bacterial diseases of plants are usually very difficult to control.  Frequently, a combination of control measures is required to combat a given bacterial disease.  Sanitation practices reduce the inoculum in a field by removing and burning infected plants or branches reduce the spread of bacteria from plant to plant by decontaminating tools and hands after handling diseased plants. Leila Geagea, PhD 25 Control of bacterial diseases of plants  Fertilizing and watering to be adjusted so plants are not extremely succulent during the period of infection.  Crop rotation very effective with bacteria that have a limited host range; impractical and ineffective with bacteria that can attack many types of crop plants. Leila Geagea, PhD 26 Control of bacterial diseases of plants  Use of resistant crop varieties supplemented with proper cultural practices and chemical applications, are the most effective means of controlling bacterial diseases, especially when environmental conditions favor the development of disease.  Soil treatment solarization, with steam or with chemicals practical only in greenhouses and in small beds or frames. Leila Geagea, PhD 27 Control of bacterial diseases of plants  Seed treatment If infested superficially  disinfection with HCl solutions or  by soaking it for several days in a weak solution of acetic acid. Treating seed with hot water does not usually control bacterial diseases because of the relatively high thermal death point of the bacteria  but treatment at 52°C for 20 minutes often considerably reduces the number of infected seeds. Leila Geagea, PhD 28 Control of bacterial diseases of plants  Chemical control as foliar sprays, copper compounds give the best results  Bordeaux mixture, fixed coppers, and cupric hydroxide are used most frequently for the control of bacterial leaf spots and blights;  Zineb, maneb, or mancozeb mixed with copper compounds are used. Leila Geagea, PhD 29 Control of bacterial diseases of plants  Antibiotics can be applied as sprays or as dips for transplants  streptomycin or a mixture of streptomycin and oxytetracycline.  Biological control Treatment of tubers, seeds, and so on with antagonistic bacteria and spraying of aerial plant parts with bacteria antagonistic to the pathogen have given control of various diseases.