This document provides an overview of a course on plant pathology and diseases of field crops. The course is taught by K. M. Golam Dastogeer in the Department of Plant Pathology at Bangladesh Agricultural University. The document discusses various topics that will be covered in the course, including the definition and necessity of pathogen dissemination, types of dispersal, and modes of pathogen dissemination such as wind, water, humans, birds, insects, and animals. It provides examples of different pathogens dispersed by these various modes and factors affecting wind dissemination. The role of insects, humans, birds, farm animals, and other agents in pathogen dispersal is also summarized. Finally, recommended textbooks on plant pathology are listed.
2. DISPERSAL OF PLANT PATHOGENS
COURSE NO. PPATH 322
COURSE TITLE: PRINCIPLES OF PLANT PATHOLOGY AND DISEASES OF FIELD CROPS
K. M. GOLAM DASTOGEER
LECTURER
DEPARTMENT OF PLANT PATHOLOGY
BANGLADESH AGRICULTURAL UNIVERSITY
3. Topics
1. What is DISSEMINATION of plant
pathogens
2. Necessity of dissemination
3. Types of dispersal
4. Modes of pathogen dissemination
a. Winds, Water, Human, Birds, Insects,
Animals—Indirect
b. Seed, plant parts, Soil-----direct
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4. Dissemination/dispersal/transmission
Transport of spores or infectious bodies, acting as
inoculum, from one host to another host at various
distances resulting in the spread of the disease.
or
Displacement of a plant pathogen from its
place of production or origin to a suitable
place where it can grow/establish
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5. EFFECTIVE DISPERSAL
If displacement occurs on a susceptible host and where
the environment is suitable, the pathogen can grow and
multiply
Ineffective Dispersal
When plant pathogen does not get any medium for its survival.
For example, if it falls on a stone
8. The dispersal of infectious plant pathogens in space occurs
through two ways:
Disease
1. Autonomous or direct or active dispersal
In this method the dispersal of plant pathogens
takes place through soil, seed and planting
material during normal agronomic operations.
There is no major role of external agencies like
insects, wind, water, etc. in this type of dispersal.
2. Indirect or passive dispersal------- insects, wind,
water, etc. in this type of dispersal insects, wind,
water, Human
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9. Wind as a means of dispersal
Short distance dissemination
sporangia of downy mildew fungi,
conidia of powdery mildew fungi
and basidiospores of rust fungi
Long Distance
•Uredospores of rust fungi, Chlamydospores of smut fungi
and conidia of Alternaria, Helminthosporium and Pyricularia,
10. Wind
Wind disseminating fungi
Bacteria
•Numerous spore
•discharge of spores with sufficient force X. malvacearum, Erwinia amylovora
• Light in weight
Nematode
• smaller size
Anguina tritici, Heterodera
•Thich outer wall
•Less affinity to water
Virus Vector
•19 Viruses and phytoplasmas –
•E.g. Most fungi except synchytriaceae, • insect and mite vectors by wind
Plasmodiophoromyces, fusarium
11. Factors affecting wind disemination
•
•
•
Periodicity of wind
– Diurnal
– Nocturnal
Turbulance in air
Air current
– Steady-horizontal
– Breeze & turbulance-Vertical
– Irregular-Multidimensional
Record of air velocity and direction tells the direction and distance of spore
dispersal and thereby helps to forecast neww disease outbreak is likely to
occur
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12. Some Example:
•P.Graminis tritici
• Horizontal---600Km
• Altitude-------500m above of the infected field
•P. Infestans
• Horizontal---200m to 600Km
•Spores of Molds
•Aspergillus
•Penicillium
•Cladosporium
• Altitude----------2000m above
13. International Dispersal
From America to Europe ---------------------------Puccinia Striformis
From Newzealand to Austrslia--------------------P. Striformis
From England to Denmark--------------------------Powdery Mildew of Barely
Glass with glycerine
Microscope
Fig. Spore Trap
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14. Dispersal by water
Surface running water
after heavy rains
during irrigation: canals and wells
Ex: The mycelial fragments, spores or sclerotia of fungi,
Colletotrichum falcatum, Fusarium, Ganoderma, Macrophomina,
Pythium, Phytophthora, Sclerotium, etc.,
Long distance ------ floods
15. By rain splash ------------splash dispersal
•
•
•
•
Most efficient meas for bacteria.
Rain drops falling with force on sori, pustules, cankers or even soil surface
may splash the propagules
– in small droplets and enable them to land on neighbouring healthy
susceptible surfaces or
– the water droplets may be carried to long distances by air.
Ex: Bacterial leaf spot of rice (Xanthomonas campestris pv. oryzae),
Bacterial leaf streak of rice (Xanthomonas campestris pv. oryzicola)
Fungal spores and bacteria present in the air or plant surface are washed
downward by rain splash or drops from overhead irrigation and are
deposited on susceptible healthy plants.
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16. 1) Animate agents
Insects
Fungal pathogens:
honey secretions having attractive odours.
Ex: Sugary disease of sorghum
Bacterial pathogens
Cucumber wilt- E. tracheiphila --------stripped cucumber beetles (Acalymma vittata) a---------spotted cucumber beetle (Diabrotica undecimipunctata).
Viral pathgens:
• More than 80 % of viral and phytoplasmall diseases
• Laegest family- Homoptera- Aphids and leaf hoppers
• mealy bugs and scale insects (Coccoidae)
• whiteflies (Aleurodidae)
•
hoppers (Membracidae) in Homoptera also transmit virus diseases.
•
17. •
Mechanical
– Fungi-----------------------------Legs
– Bacteria--------------------------Bristles
– Viruses---------------------------Wings
– Mycoplasma--------------------Abdomen
• Biological
Transmit through sexual process from generation to generation
Insect
Specificity of Insect Transmission
Aphids----------------Mosaic group---------------Tomato mosaic, Papaya mosaic, potato leaf roll, chilli mosaic
Leaf Hopper---------Yellows ---------------------------------Tungro of rice
Thrips------------------Spots with concentric ring---------Pineaple yellow spots
Whiteflies-------------Thickening of veins/veinlets------Tobacco leaf curl, Tomato leaf curl
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18. e) Human beings- more direct than indirect
•
•
•
•
•
•
•
Transportation of seeds (seed trade): Ex: Late blight of potato, Downy
mildew of grapevine, Citrus canker, Fusarium wilt of banana, etc.
Planting diseased seed materials: Planting diseased bulbs, bulbils,
corms, tubers, rhizomes, cuttings, etc., of
During adoption of normal farming practices:
Cultivation, planting, irrigation, weeding, pruning etc.,
Spores can be carried by workers clothing’s, shoes, and hands etc.,
By use of contaminated implements:
By use of diseased grafting and budding material
19. f) Dispersal by phanerogamic parasites:
• Phanerogamic parasites transmit the viruses by acting as a
bridge between the diseased and healthy plants.
• Ex: Dodder(Cuscuta California, C. campesris, C. subinclusa
etc.)
• Cuscuta subinclusa----Cucumber mosaic virus
• Cuscuta california -----Tobacco mosaic virus, Tobacco rattle
virus, Tomato spotted wilt virus
• Cuscuta campestris - Tomato bushy stunt virus
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20. g) Role of birds
• Disperse flowering parasites and certain fungi.
• Stem segments of dodder are carried by birds for preparing
their nests
• Seeds of Loranthus
• Spores of chestnut blight fungus
• Cleistothecia of many powdery mildew fungi are carried by
feathers of birds.
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21. Farm and wild animals:
Cattle feeding on diseased fodder ingest the
viable fungal propagules (spores or oospores
or sclerotia) and pass out as such in the dung.
soil inhabiting fungi especially sclerotia adhere
to the hoofs and legs of animals and get
transported to other places.
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