SURVIVAL OF PHYTOPATHOGENIC BACTERIA Phytopathogenic bacteria have the ability to survive both for longer & shorter periods including soil, seed, diseased crop debris, weed host, and insect vectors. DISPERSAL OF PLANT PATHOGENIC BACTERIA To make a healthy plant diseased, the first requirement of a pathogen is to spread its inoculum (primary as well as secondary) from the source of survival to the susceptible parts of a healthy plant. The spread of a plant pathogen within the general area in which it is already established is called “dispersal” or “dissemination”. Moving the inoculum only a few inches and transporting it for hundreds of miles both constitute its dispersal or dissemination. However, pathogen dispersal is not necessary only for the spread of diseases but also for the continuity of the life-cycle and evolution of the pathogen. Detailed knowledge of pathogen-dispersal is essential to find out effective control measures for diseases because the possibilities of preventing dispersal and thereby breaking the infection chain always exist.

1. Presented By:
Om Prakash Barik
Adm. No. – 20222217
1st Yr. MSc. Ag. (Plant Pathology)
College Of Agriculture, OUAT, BBSR
ODISHA UNIVERSITY OF AGRICULTURE
AND TECHNOLOGY
College Of Agriculture, Bhubaneswar
PLANT BACTERIOLOGY
(Pl. Path 503) (2+1)
Assignment Topic:
SURVIVAL AND DISPERSAL OF
PHYTOPATHOGENIC BACTERIA
Submitted To:
Dr. Akshay Kumar Senapati
HOD & Professor
Dept. of Plant Pathology
College Of Agriculture, OUAT, BBSR

2. SURVIVAL OF PHYTOPATHOGENIC BACTERIA
Phytopathogenic bacteria have ability to survive both for longer & shorter
periods including soil, seed, diseased crop debris, weed host, insect
vectors.
1. Soil
 Bacteria as transient visitors, resident visitors and residents.
 Ttransient visitors: have no population increase and rapid population
decline in soll. Most of foliar effecting bacteria
 For example, Xanthomonas campestris pv. campestris survives less
than 2 weeks in soil summer.
 Rresident visitors: Pulations of resident visitors, such as soft rotting
Pantoea, Erwinia, decline gradually or they increase depending on
hosts.
 Residents: Soft rotting bacteria pseudomonas and Bacillus spp.
maintain their population in soil.
2. Plant Debris
 Contaminated plant debris serves as a means of survival of foliar
pathogens.
 Duration of survival increases if this debris remains on the surface
rather than being buried deep in the soil.
 Generally, the bacterial population decline sharply as the organic
residue decomposes and deep burial hastens decomposition through
providing moisture, temperature and other congenial conditions for
decomposition
 E.g.,
 Xanthomonas campestris pv. malvacearum can survive 40-100
days until the supporting cotton debris was thoroughly
decomposed

3.  X. campestris pv. malvacearum could survive 6 months on the
soil surface and only 3 met when the cotton debris was buried
15 cm.
3. Seed
 Seed acts as a means of survival for many bacterial plant pathogens.
Understanding the nature of seed infection is important if the
treatments are to eliminate pathogens.
 The bacteria adhere to the seed coat, or lodged among the seed
hairs or may remain beneath the seed at or in deeper seed tissues.
 E.g.,
 X. campestris pv.campestris - Black rot of crucifers
 X campestris pv.malvacearum - bacterial blight of cotton
 X. oryzae pv.oryzae - bacterial blight of paddy
4. Insect – Vectors
 Insect-vectors play important role both in disseminating as well as
over wintering the bacterial ant pathogens
 The bacterium Pantoea stewarti can survive more than a month in
digestive tract of active corn flee beetle (Chaeronema pulicaria).
 Psyringae pv. savastonoi (incitant of olive knot) can survive in the
digestive tract throughout the life of olive fruit fly.
 The olive knot bacterium forms a significant part of intestinal
microflora; apparently, the bacterium makes host nutrients available
to the developing larvae
 E.g.,
 Pantoea stewartii lives in corn flea beetle digestive tract for
more than 1 month
 P. syringae pv. savastonoi cause olive knot & can survive in
insect olive fruit fly for throughout the fruit fly life

4. 5. Weeds or collateral hosts, volunteer crop
 Weeds or collateral hosts, volunteer crop plants play important role
in the survival of plant pathogenic bacteria. Solanum cineacum and S.
nigrum supports Ralstonia solanacearum. Many weed or non-host
plants support an epiphytic microbial population, which may include
plant pathogenic bacteria.
 E.g.,
 Xanthomonas campestris pv phaseoli is reported to urvive
epiphytotically on leaves of weeds hosts for up to 21 days. A
number of soil invading bacteria survive on the roots of non-
hosts or weed hosts.
 Xanthomonas oryzae pv. oryzae cause bacterial leaf blight of
rice, it can survive on weeds like Leersia hexandra, Loryzoides
oryzoides var. japonica., Zoysia sp.., Echinochloa, crussgali,
Leptochloa chinensis, Cyperus rotundas.
 Ralstonia solanacearum cause bacterial wilt of solanceous
plants can survive on Solanum nigrum & S. cineaeum for
throughout the life of weed

5. DISPERSAL OF PLANT PATHOGENIC BACTERIA
To make a healthy plant diseased, the first requirement of a pathogen is
spread of its inoculum (primary as well as secondary) from the source of
survival to the susceptible parts of healthy plant. The spread of a plant
pathogen within the general area in which it is already established is called
“dispersal” or “dissemination”.
Moving the inoculum only a few inches and transporting it for hundreds of
miles both constitute its dispersal or dissemination. However, the
pathogen-dispersal is not necessary only for spread of diseases but also for
continuity of the life-cycle and evolution of the pathogen. A detailed
knowledge of pathogen-dispersal is essential to find out effective control
measures for diseases because the possibilities of preventing dispersal and
thereby breaking the infection-chain always exist.
Dispersal of plant pathogenic bacteria generally occurs through two major
modes:
1. Autonomous (direct or active) dispersal and 2. Passive (indirect)
dispersal.
Mode # 1. Autonomous (Direct or Active) Dispersal:
In this case the pathogens get dispersed either by their own movement or
by the movement of the source they belong; no intervention of any
external agency like insects, air, water, etc. is involved. For instance,
autonomous dispersal of plant pathogens is accomplished through the
agency of soil, seed, plant and plant organs during normal agronomic
operations.
However, following are important modes of autonomous dispersal of plant
pathogens:

6. I. Seed Dispersal
 The seeds generally serve as medium for autonomous dispersal of
pathogens when they either get contaminated with pathogens or
contain pathogens on their seed coats or contain them inside.
 To exemplify autonomous dispersal of pathogens remaining intact on
seed coats, one can find diseases like bacterial black arm disease of
cotton or angular leaf spot of cotton (Xanthomonas campestris pv.
malvacearum) and black rot of crucifers (X. campestris pv. campestris)
where the pathogen remains dormant inside the seeds.
 When such an infected seed is sown in next crop season and grows,
the pathogen also glows simultaneously systemically and the disease
manifests by symptoms appearing in plants.
II. Plant and Plant Organ Dispersal
 Weeds and volunteer crop plants are known as source of survival and
dispersal of bacteria
 Most of the solanaceous weeds harbor Ralastonia solanacearum and
Clavibacter michiganense and all sps. of brassica acts as host for
Xanthomonas campestris pv campestris.
 Plants and their parts (other than seeds) prove to be good source of
pathogen dispersal. Plants generally get infected by the pathogen
already present in the field or introduced from outside.
 There exist some classic examples of this type of pathogen dispersal
the new bacterial pathogen are often introduced into new areas with
the introduction new crops.
 Psuedomonas syringae pv gplycinea was reported to be introduced
into united states and Russia with the introduction of soybean
culture from orient.
III. Soil Dispersal
 Many of the pathogens survive through soil and get dispersed.

7. Mode # 2. Passive (Indirect) Dispersal:
The passive or indirect dispersal of plant pathogens is accomplished
through the intervention of external agencies like air, water, man, insects,
nematodes, farm and wild animals, birds, and fungi.
I. Air Dispersal (Anemochory)
 Aerial strands- Many plant pathogenic bacteria exudates ooze or
slime on diseased tissue. This strands break apart into fine fragments
which then carried by dry wind to another host plant Example
Psuedomonas syringae pv mori bacterial blight of mulberry.
 Wind driven rain - The bacteria dispersed along the contaminated
water particles driven by wind. Example Clavibacter michiganense
subsp. michiganense tomato cancker
 Wind driven soil particles or dust - Example- Streptomyces scabies
potato scab
 Aerosol carrying bacteria deposits directly onto soybean leaves of
P. Syringae pv. glycinea bacterial blight of soybean.
II. Water Dispersal (Hydrochory)
 Water as an agent of plant pathogen dispersal appears in no way less
important to air, man, and insects. It generally provides for short
distance dispersal except when floods inundate large areas.
 Water-splash dispersal is one of the very efficient device by which
rain spreads plant pathogens; rain drops falling with force on
pustules, cankers, or even soil surface may splash the pathogens in
small droplets and enable them to land on neighboring healthy
susceptible host surfaces or such water droplets, may be carried to
long distances by water splash

8.  E.g.,
 P. syringae pv.syringae brown spot of bean weed host (as
epiphyte) to the natural host by rain splash.
 P. avenaenlade blight of oats upward movement of bacteria
from soil to leaves by scattering rains.
Water-flow dispersal is known to disseminate bacteria through Irrigation
water or rain water from an infested field may carry with it pathogens to
neighboring fields of healthy crops. In 1963, epidemic occurred on about
506ha of peas under sprinkler irrigation in Wisconsin due to bacterial
blight of peas caused by P. syringae pv. pisi.
III. Dispersal by Man (Anthropochory)
 Man is one of the most important agents affecting plant pathogen
dispersal in a limited area or even over distant areas.
Short Distance:
 Pathogen dispersal by man in limited areas mainly occurs through his
clothes, contaminated tools, transport of contaminated soil on feet,
equipment, etc.
 Grafting and budding between healthy and diseased plants, and
cultural operations such as hoeing, weeding, pruning easily spread
pathogens from one plant to the other.
Long Distance:
 The dispersal of plant pathogens over long distances is usually
accomplished by the transport of infected plant parts such as seeds,
nursery stocks, or timber products; the seed trade is actually the
means of dispersal in which man plays the most crucial role.
 The import and export of pathogen containing materials without
prior precautions lead to movement of pathogens from one country
to the other.

9.  E.g.,
Bacterial
Pathogen
Disease Introduce Into
Introduce
From
X.c.pv.campastris
Black rot of
crucifers
India in1929 Jawa
X.oryzae pb.
oryzae
Bacterial blight
of rice
India in1959 Philippines
X. citri Citrus canker United states Japan
Erwinia
amylovora
Fire blight of
stone fruits
Japan, New
Zealand,
Europe in 1919
North
America
P. Syringae pv
glycinea
Bacterial blight
of soybean
United states
and Russia
Orient
IV.Dispersal by Insects
 Since the discovery by Waite (1891) shows that bees and wasps
disseminate bacteria Erwinia amylovora (causing fire blight of apple
and pear), insects have been found to be one of the most important
agents for plant pathogen dispersal.
 Often insects transmits bacteria as contaminants during their feeding,
foraging, or nectar/pollen collecting activities.
 For instance, Insects are considered important for dispersal of some
bacterial pathogens.
 E.g.,
 The cucurbit-wilt causing bacterium, namely Erwinia
tracheiphila is completely dependent on cucumber beetles for
its dispersal.
 Erwinia carotovora causes black leg disease of potato is
disseminated by insects mainly Hylemya cilicrura.

10.  Pantoea stewartii, the corn wilt pathogen, perennates inside
Chaetocnema pulicaria (corn flea beetle) in their digestive
tract and is spread by the latter.
 Leaf minor insect disseminates Xanthomonas campestris pv.
citri, the causal organism of well-known citrus canker disease.
V. Dispersal by Nematodes
 Nematodes play an important role in disseminating. Although they
favor only short distance or local dissemination.
 Leafy gall disease caused by Corynebacterium fasciens is dispersed by
Aphelenchoides, an ectoparasitic nematode. Yellow carrot disease of
wheat caused by Corynebacterium tritici is disseminated by the ear
cockle nematode, namely, Anguina tritici.
VI. Dispersal by cultural practices
 As contaminant on agriculture implements there are certain cultural
practices that are responsible for bacterial pathogen dispersal.
 For instance Clavibacter michiganense pv. sepedonicus causing ring
rot of potato spread to non-infected potato see on cutting knives
contaminated with infected tubers.