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Control of Bacterial Diseases of Plants.pptx

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Control of Bacterial Diseases of Plants.pptx

  1. 1. 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. • Infestation of fields or infection of crops with bacterial pathogens should be avoided by using only healthy seeds or transplants.
  2. 2. Control of Bacterial Diseases of Plants Cultural practices • Sanitation practices aiming at reducing the inoculum in a field by removing and burning infected plants or branches, and at reducing the spread of bacteria from plant to plant by decontaminating tools and hands after handling diseased plants, are very important
  3. 3. Control of Bacterial Diseases of Plants Cultural practices…continued • Free water on susceptible leaves and optimal temperature for bacterial growth are the best combination for promoting disease by plant bacteria. • It is possible to reduce bacterial diseases in greenhouses by controlling the environment, by maintaining low relative humidity values using periodic aeration of the greenhouse and drip irrigation, and by holding suboptimal temperatures for pathogen proliferation. • In Israel, farmers have been able to reduce damage caused by P.syringae pv. lachrymans on cucumber and other vegetable crops by using rounded greenhouse structures made of plastic treated with anticondense chemicals. • These plastics avoid that water drops fall on leaves
  4. 4. Control of Bacterial Diseases of Plants Cultural practices…continued • Adjusting fertilizing and watering so that the plants are not extremely succulent during the period of infection may also reduce the incidence of disease. • In general disease incidence can be lowered by avoiding excess use of nitrogen fertilizers. •
  5. 5. Control of Bacterial Diseases of Plants Cultural practices…continued • Crop rotation can be very effective with bacteria that have a limited host range, but is impractical and ineffective with bacteria that can attack many types of crop plants.
  6. 6. Control of Bacterial Diseases of Plants • Cultural practice…continued • A variety of cultural practices help to reduce losses due to bacterial wilt. • In regions or fields where R. solanacearum is not present, • the fist line of defense is to avoid introducing the pathogen by using pathogen-free propagative tissue (e.g., tubers and rhizomes) and good sanitation. • In some developed countries, regulatory agencies have • promulgated quarantine regulations for biovar 2 (race 3) strains.
  7. 7. Control of Bacterial Diseases of Plants Cultural practice…continued • These may include testing all lots of seed potatoes for latent infection, surveying ware and starch potatoes and destroying loads containing any infected tubers, monitoring surface water and prohibiting use of contaminated waterways for irrigation, and requiring that affected farms disinfest machinery, storage facilities, etc. and plant grasses in infested fields for 4 or 5 years
  8. 8. Control of Bacterial Diseases of Plants Cultural practice…continued • Planting clean seed potatoes is helpful even in regions where the pathogen is endemic, but in developing countries there may not be enough certified seed tubers or they are too expensive for subsistence farmers. • An innovative on-farm seed-plot technique pioneered in eastern Africa has the potential to help satisfy farmer s needs for high quality, pathogen-free seed potatoes. • Where R. solanacearum is already endemic, the best cultural control is crop rotation. • Several grasses are especially effective in reducing BW incidence
  9. 9. Control of Bacterial Diseases of Plants Resistant varieties(Y) • The use of crop varieties resistant to certain bacterial diseases is one of the best ways of avoiding heavy losses. • Varying degrees of resistance may be available within the varieties of a plant species, and great efforts are made at crop breeding stations to increase the resistance of, or introduce new types of resistance into, currently popular varieties of plants. • Resistant 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.
  10. 10. Control of Bacterial Diseases of Plants Resistant varieties(Y)…continued • Host-specific P. syringae pathovars show a typical gene-for-gene interaction with their host and resistance against them is generally mediated by major resistance genes. • Breeding programmes and tolerant or resistant host cultivars have been developed for various economic important pathovars of P. syringae including pv. morsprunorum, pv. phaseolicola, pv. pisi , pv. tabaci, pv. Tomato and pv. Glycinea. • Resistance genes against P. syringae pathovars have been mapped or cloned in tomato bean pea and soybean . • In addition, various resistance genes against P. syringae pathovars have been cloned in Arabidopsis.
  11. 11. Control of Bacterial Diseases of Plants • Disinfection and sterilization • Soil infested with phytopathogenic bacteria can be sterilized with steam or electric heat and with chemicals such as formaldehyde, but this is practical only in greenhouses and in small beds or frames. • Seed, when infested superficially, can be disinfested with sodium hypochlorite or HCl solutions or by soaking it for several days in a weak solution of acetic acid. • If seeds can remain for 2 to 3 days in fermenting juices of fruit in which they are borne, bacterial pathogens can be eliminated. • When the pathogen is inside the seed coat and in the embryo, such treatments are ineffective. • 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.
  12. 12. Control of Bacterial Diseases of Plants Seed treatment • Various pathovars of P. syringae are seedborne including  P.s. pv. coronafaciens on cereals,  P.s. pv. glycinea on soybean,  P.s. pv. lachrymans on cucurbits,  P.s. pv. maculicola on brassicas,  P.s. pv. phaseolicola on bean,  P.s. pv. pisi on pea, P.s. pv. porri on leek,  P.s. pv. tabaci on tobacco, and P.s. pv. tomato on tomato (Smith et  al., 1988). • The first consideration in controlling these pathogens is to obtain • pathogen-free seed. • This can be achieved by seed production in arid regions, seed certification by serological or molecular techniques, chemical treatment of seeds with antibiotics or copper-based compounds or heat treatment of seeds (Kritzman,1993; Bashan and de Bashan, 2002).
  13. 13. Control of Bacterial Diseases of Plants Use of chemicals • The use of chemicals to control bacterial diseases has been, generally, much less successful than the chemical control of fungal diseases. • Of the chemicals used as foliar sprays, copper compounds give the best results. • However, even they seldom give satisfactory control of the disease when environmental conditions favor development and spread of the pathogen. • Bordeaux mixture, fixed coppers, and cupric hydroxide are used most frequently for the control of bacterial leaf spots and blights. • Bacterial strains resistant to copper fungicides, however, are quite common. • Zineb, maneb, or mancozeb mixed with copper compounds is used for the same purpose, especially on young plants that may be injured by the copper compounds
  14. 14. Control of Bacterial Diseases of Plants Copper-based fungicides • Since the use of antibiotics is restricted in most European countries, copper-based fungicides are the only effective compounds available to the farmer to control bacterial plant diseases. • Copper-based fungicides such as Bordeaux mixtures are used extensively to control bacterial pathogens on fruit trees such as P. syringae pv. syringae and P. syringae pv. morsprunorum on stone fruit trees. • The use of copper, however, has several disadvantages. Phytotoxicity can occur and resistance to copper develops rapidly in bacteria
  15. 15. Control of Bacterial Diseases of Plants Copper-based fungicides… continued • Hwang et al. (2005) have recently shown that most P. syringae strains are copper resistant. • Copper resistance genes, including the copABCD operon and a copRS two- component regulatory system are present in the genome of P. syringae pv. syringae B728a (Feil et al., 2005). • These proteins appear to be 92-96% identical to plasmid-encoded CopABCDRS proteins found in other strains of P. syringae.
  16. 16. Control of Bacterial Diseases of Plants Antibiotics • Antibiotics have been used against certain bacterial diseases with mixed results. Some antibiotics are absorbed by the plant and are distributed systemically. • They can be applied as sprays or as dips for transplants. • The most important antibacterial antibiotics in griculture are formulations of streptomycin or of streptomycin and oxytetracycline. • Unfortunately, bacterial races resistant to antibiotics develop soon after widespread application of antibiotics; in addition, no antibiotics are permitted on edible plant produce.
  17. 17. Control of Bacterial Diseases of Plants Antibiotics… continued • The use of antibiotics for the treatment of bacterial diseases on plants is modest relative to applications in human and veterinary medicine. Because they are relatively expensive, antibiotics are used primarily on high-value fruit and vegetable crops and ornamental plants. • Streptomycin, an aminoglycoside antibiotic, has been the major antibiotic used on plants in the USA.
  18. 18. Control of Bacterial Diseases of Plants Antibiotics… continued • In Europe, streptomycin is either not permitted, only used on an emergency basis, or used regularly, depending on the country. • Streptomycin is used to control various pathovars of Pseudomonas syringae, which cause fruit-spotting or blossom-blast symptoms on apple, pear and related landscape trees.
  19. 19. Control of Bacterial Diseases of Plants Antibiotics… continued • On tobacco streptomycin is used to control wildfire, caused by Pseudomonas syringae pv. tabaci. • Another Pseudomonas pathogen that is targeted is P. cichorii on celery, where it causes bacterial blight (McManus et al.,2002). • Oxytetracycline, a tetracycline antibiotic and gentamcyin, an aminoglycoside • antibiotic, are used to control Pseudomonas spp. on several vegetable crops in Latin American countries.
  20. 20. Control of Bacterial Diseases of Plants Antibiotics… continued • The emergence of streptomycin-resistent plant pathogens has complicated the control of bacterial diseases of plants. Resistance to streptomycine has been reported in P. cichorii, P. syringae pv. lachrymans, P. syringae pv. papulans and P. syringae pv. syringae (McManus et al., 2002) • Resistance to streptomycin in Pseudomonas bacteria is plasmid/transposon determined. •
  21. 21. Control of Bacterial Diseases of Plants • Antibiotics… continued • The linked strA-strB genes that encode streptomycin-inactivating phosphotransferases are located on variants of transposon Tn5393 which are present in P. syringae pv. syringae. • The streptomycin resistance transposon Tn5393a, which carries a strA-strB determinant is found in the P. syringae pv. syringae B728a genome (Feilet al., 2005)
  22. 22. Control of Bacterial Diseases of Plants Biological control • Successful practical biological control of the bacterial plant disease crown gall has been obtained by treating seeds or nursery stock with bacteriocin-producing antagonistic strains of Agrobacterium. • 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 under experimental conditions but have been less successful in practice • Perhaps the best known example of biological control against plant pathogenic bacteria, including plant pathogenic Pseudomonads, is the use of ice nucleationdeficient deletion mutants of P. syringae and P. fluorescens to prevent or reduce the growth of frost-forming bacteria on leaves and blossoms. • This research has led to commercial products such as Frostban that can be used on fruit crops, almond, potato, and tomato crops
  23. 23. Control of Bacterial Diseases of Plants Biological control…continued • There are various examples of plant growth promoting rhizobacteria (PGPR) such as Pseudomonas and Bacillus spp. (Kloepper et al., 2004) that can control leaf pathogens including pathovars of P. syringae via induced systemic resistance. • Mixtures of PGPRs, mainly Bacillus strains, have been used in field trials to control angular leaf spot caused by P. syringae pv. lachrymans on cucumber. • Induced systemic resistance used in combination with other strategies was effective in controlling bacterial speck on tomato
  24. 24. Control of Bacterial Diseases of Plants Biological control…continued • Mainly bacterial antagonists, have been tested to control pathovars of P.syringae under field conditions. • Volksch and May (2001) describe the use of near isogenic or ecologically similar antagonistical strains to target P. syringae pv.glycinea under field conditions. • Strains of Pantoea agglomerans suppressed the development of basal kernel blight of barley, caused by Pseudomonas syringae pv.syringae, Under field conditions, 45 to 74% kernel blight disease reduction was • observed (Braun-Kiewnick et al., 2000). • A non-pathogenic P. syringae strain gave some control in field trials at various locations in the USA and Canada against bacterial speck (Wilson et al., 2002).
  25. 25. Control of Bacterial Diseases of Plants IPM(IDM) • Control of plant pathogenic bacteria is difficult and there is not one strategy that is 100% effective. • However, sanitary measures, combined with cultural, chemical and/or biological strategies may lead to satisfactory disease control. • For control bacterial wilt • No single strategy can reduce the incidence and/or severity of BW in regions where the pathogen is endemic ( Saddler, 2005). • Nevertheless, losses due to BW can be greatly reduced by following a holistic approach, often referred to as Integrated Disease Management (IDM),
  26. 26. Control of Bacterial Diseases of Plants IPM(IDM)…continued • IDM employs multiple disease control strategies. For BW, all successful IDM packages include use of pathogen-free planting material, planting less susceptible host varieties, and rotation of susceptible crops with those resistant or immune to BW
  27. 27. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS • The most common types of bacterial diseases of plants are those that appear as spots of various sizes on leaves, stems, blossoms, and fruits. • In some bacterial diseases the spots continue to advance rapidly and the diseases are then called blights. • In severe infections the spots may be so numerous that they destroy most of the plant surface and the plant appears blighted or the spots may enlarge and coalesce, thus producing large areas of dead plant tissue and blighted plants. • The spots are necrotic, circular or roughly circular, and in some cases are surrounded by a yellowish halo. In dicotyledonous plants the bacterial spots on some hosts are restricted by large veins, and the spots appear angular.
  28. 28. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS…continued • For the same reason, bacterial spots on monocotyledonous plants appear as streaks or stripes. • In humid or wet weather, infected tissue often exudes masses of bacteria that spread to new tissues or plants and start new infections. • In such weather, dead leaf tissue often tears up and falls out, leaving holes that are round or irregular in shape with ragged edges.
  29. 29. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS…continued • Almost all bacterial spots and blights of leaves, stems,and fruits are caused by bacteria in the genera Pseudomonas and Xanthomonas. • Pseudomonas syringae, pathovars (pv.) causing wildfire of tobacco (P. syringae pv. tabaci), • angular leaf spot of cucumber (P. syringae pv. lacrymans), • Halo blight of beans (P. syringae pv. phaseolicola), • Citrus blast, pear blast, bean leaf spot, and lilac blight (P.syringae pv. syringae), and bacterial speck of tomato (P. syringae pv. tomato)
  30. 30. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS… continued • Xanthomonas compestris, pathovars causing common blight of beans (X. campestris pv. phaseoli), • angular leaf spot of cotton (X. campestris pv.malvacearum), • bacterial leaf blight of rice (X.campestris pv. oryzae), bacterial blight or stripe of cereals (X. campestris pv. translucens), • Bacterial blight of cassava (X. campestris pv. manihotis), • bacterial spots of stone fruits (X. arboricola pv.pruni) and of tomato and pepper (X. campestris pv. vesicatoria)
  31. 31. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS… continued • In bacterial spots and blights, routine diagnosis of the disease depends on the morphology of the symptoms, the absence of pathogenic fungi, and the presence of bacteria in recently infected tissue. • Microscopic distinction among these pathogens is impossible, as it is among most plant pathogenic bacteria. • The bacteria overwinter on infected or healthy parts, especially buds, of perennial plants, on or in seeds, on infected plant debris, on contaminated containers or tools, and on or in the soil.
  32. 32. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS… continued • Their spread from the place of overwintering to their hosts and from plant to plant takes place by means of rain, runoff, rain splashes, windblown rain, direct contact with the host, insects such as flies, bees, and ants, handling of plants, and tools. • Penetration takes place through stomates, hydathodes, and injuries.
  33. 33. Some common bacterial diseases BACTERIAL SPOTS AND BLIGHTS… continued • Water soaking of tissues during heavy rains greatly favors penetration and invasion by bacteria. • Bacteria multiply on walls of host cells, which collapse after disruption of the cell membrane. • The control of bacterial spots and blights can be obtained to some extent by the use of resistant varieties, crop rotation, and sanitation. • Some control can be obtained by spraying several times during the period of plant susceptibility with chemicals such as copper compounds mixed with zineb, maneb, or mancozeb antibiotics such as streptomycin and tetracyclinesand, in some cases, with plant defense activators
  34. 34. Some common bacterial diseases BACTERIAL VASCULAR WILTS • Vascular wilts caused by bacteria affect mostly herbaceous plants such as several vegetables, field crops, ornamentals, and tropical plants. • The bacteria and the most important vascular wilts they cause are listed. • Clavibacter (Corynebacterium), causing ring rot of potato (C. michiganense subsp. sepedonicum) and • bacterial canker and wilt of tomato (C. michiganense subsp. michiganense) • Curtobacterium (Corynebacterium) flaccumfaciens, causing bacterial wilt of bean
  35. 35. Some common bacterial diseases BACTERIAL VASCULAR WILTS…continued • Erwinia, causing bacterial wilt of cucurbits (E. tracheiphila), • and fire blight of pome fruits (E. amylovora) • Pantoea, causing Stewart’s wilt of corn (P. stewartii) • Ralstonia, causing the southern bacterial wilt of solanaceous crops and the Moko disease of banana (R. solanacearum) • Xanthomonas, causing black rot or black vein of crucifers (X. campestris pv. campestris)