Control of Bacterial Diseases of Plants.pptx

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.

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

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

• 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.
•

• 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.

• 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.

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

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

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.

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.

• 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.

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).

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

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

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.

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.

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.

• 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.

• 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.

• 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.
•

• 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)

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

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

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).

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),

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

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.

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.

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)

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)

• 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.

• 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.

• 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

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

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)

Control of Bacterial Diseases of Plants.pptx

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