Plant Disease Recognition and Management, modified.pdf

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1. PLANT DISEASE RECOGNITION
AND
MANAGEMENT
PATRIA LUISA G. GONZALES

2. OBJECTIVES:
At the end of the lesson, the participants must be
able to:
•Know the steps in plant disease recognition
•Recognize common symptoms caused by
pathogens
•Explain the general principles and methods
of disease management

3. Steps in plant disease diagnosis
1. Know what is normal
•proper plant identification
•recognize healthy plant appearance
2. Check for symptoms and signs
•identify characteristic symptoms
•identify symptom variability
•look for signs of biotic causal agents
•identify plant parts affected
3. Observe patterns
•check distribution of patterns
•check for host specificity
4. Ask questions
•review the cultural practices and environmental conditions
5. Laboratory tests
•incubation of plant materials
•isolation and identification of causal
•diagnostic tests for identification of biotic causal agents
•diagnostic tests for identification of abiotic causal agents
6. Final diagnosis

4. Disease
Any physiological disturbance brought about
by a pathogen or environmental factor that
prevents the normal development of a plant
resulting to changes in appearance and reduces
its economic value.

5. DISEASE
Susceptible
HOST
Virulent
PATHOGEN
Favorable
ENVIRONMENT
The Disease Triangle

6. Noninfectious or Abiotic Causes
•extreme temperatures
•extreme soil moisture
•extreme light
•lack of oxygen
•air pollution
•nutrient deficiencies
•mineral toxicities
•high or low ph
•pesticide toxicity
•improper cultural practices

7. PATHOGENS
Entities or organisms that cause diseases in susceptible hosts (plants)
under favorable environmental conditions.

8. •Fungi – small eukaryotic, usually
filamentous, branched, spore
bearing organisms that lack
chlorophyll
Classification
•Bacteria - small, one-celled organisms
that reproduce by binary fission
•Nematodes – are small thread-like,
unsegmented round worms

9. Classification, con’t
•Phytoplasmas – are tiny organisms without
rigid cell wall and bounded only by a
unit membrane
•Viruses– are complex entities made
up of nucleic acid core and a
protein coat that infect, multiply,
mutate and act like a living
organism inside the cells
•Viroids– are much smaller than viruses
and have no protein coat, only
“naked” RNA

10. Pathogens cause diseases by:
1)Killing the host cells or slowing down their metabolism with
enzymes i.e. Bacterial soft rot or with toxins i.e. Leaf spots and
leaf blights
2)Blocking the passage of food, water or nutrients as in vascular
wilts
3)Absorbing or consuming the cell contents as in powdery mildew
4)Taking over the genetic control of the plants as in virus
multiplication or replication in infected cells depriving the plant
cells of necessary compounds for growth and development
5)Multiplying in great numbers of the surfaces of stems and leaves,
blocking sunlight and slowing down the diffusion of gases
thereby impairing photosyntesis i.e sooty molds
6)Prodicing hormones or growth regulators resulting in hypeplasia
(increased cell number) or hypertrophy (increase in cell size) i.e.
Root galls or club root

11. MODE OF DISSEMINATION
•Soilborne
•Airborne
•Waterborne
•Insectborne
•Seedborne
MODE OF INGRESS
•Natural openings
•Wounds
•Direct penetration
•Vectors feeding
Indirect
Direct

12. Stomata
Natural openings
Hydathode
Type of secretory tissue in
leaves, usually angiosperms,
that secretes water through
pores in the epidermis or
margin of leaves
Lenticels
airy cells in the bark of stems
and roots
A stoma (also stomate;
plural stomata) is a tiny
opening or pore used for
gas exchange; mostly found
on the under-surface of
plant leaves.

13. Direct penetration, vectors feeding
Leafhoppers
Nematodes
Spores

14. SYMPTOMS
Expressions by the host plant of a
pathologic condition by which a particular
plant disease may be distinguised
from other diseases

15. Blight – sudden discoloration and
death of tissues over a certain
portion of the plant (leaves
including the veins or parts of
the leaves; could also occur on
flowers and stems
i.e. Sheath Blight (Rice) caused by
Rhizoctonia solani
Blister - localized swellings or
enlargement of epidermal cells due to
excessive accumulation of water is termed
intermuscence and the diagnostic
symptom is the appearance of a
i.e. White blister in brassica
caused by Albugo candida
Common Symptoms

16. Canker – sunken dead areas on fruits
stems, leaves, tubers, and
roots which are surrounded by
a callus from adjacent living/
healthy tissues
i.e. Citrus canker
Chlorosis – yellowing of normally green
tissues due to the partial failure of
the chlorophyll to develop
i.e. Rice tungro

17. Damping off – sudden wilting and toppling
over of seedlings as a result of
extensive necrosis of tender tissue
of the roots and stem near the soil
line
i.e. Damping off (Tomato)
Die–back - dying backwards from tips of
twigs and branches of trees
i.e. Dieback disease of citrus

18. Firing - sudden drying, collapse and death
of entire leaves in response to the
activity of root rot and vascular wilt
pathogens
i.e. Fire blight (Apple) caused by
Erwinia amylovora
Gall/tumor – masses of undifferentiated
growth i.e. Galls in roots of celery
infected with root knot Meloidogyne
incognita

19. Gummosis – exudates are produced
from diseased woody
tissues
i.e. Gummosis of Mang
caused by Lasiodiplodia
theobromae
Mosaic – intermingling of patches of
normal (green tissues) and
chlorotic (light green or
yellowish) areas
i.e Leaf Mosaic (banana)

20. Rosette – short bunchy habit of plant
growth
Rots – host’s cell walls are broken
down resulting in the exudation
of juices from the infected
tissue. The infected part becomes
pulpy and a foul smell often
develops due to colonization by
secondary invaders.
i.e. Black rot of Pineapple

21. Scald – blanching of epidermal and
adjacent tissues of fruits and
leaves
i.e. Leaf Scald (Rice) caused
by Microdochium oryzae
Scab – a raised, roughened or
abnormal thickening, discrete
lesions on the surface of a
plant organ or tissue
i.e. citrus scab

22. Spot - is a relatively small, distinct
lesion, with definite borders
(well defined gray or brown
necrotic tissue
i.e Black Sigatoka in banana
caused by Mycosphaerella
fijiensis
Stunting– reduced growth rate
i.e. Grassy stunt (rice)

23. Wilt – whole plants or leaves
droop indicating problems
with water intake
i.e Fusarium wilt ( banana)
caused by Fusarium
oxysporum f.sp. cubense

24. Signs
refer to structures of the pathogen that are found to be associated
with the infected plant

•Conidia, conidiophores, mycelia
•Fruiting bodies i.e. pycnidia
IRRI Rice Knowledge Bank
IRRI Seed Health Unit
conidia and conidiophore
of Bipolaris oryzae
Spore ball with teliospores of
Ustilaginoidea virens
mycelia, conidiophore, and
conidia of Penicillium sp.
Nectria cinnabarina
Pilobolus sp.
Phoma sp.

25. Corn roots infected with Hoplolaimus galeatus, lance
nematode, stained
Dep’t of Crop Science, illinois
•Bacterial ooze
Signs, cont’d
•Nematodes, different growth stages

26. PRINCIPLES AND METHODS
OF
PLANT DISEASE CONTROL

27. PRINCIPLES
•Exclusion – the agent can be prevented from gaining access
into the cropping area
•Eradication – the agent can be destroyed or removed if it is
already in the cropping area
•Protection – the plant may be equipped or surrounded by
various barriers to prevent the agent from getting
into it
•Immunization/Resistance – the nature of the plant may be
changed such that after having gained access, the
agent will be rendered incapable of causing a
series of distrubances to the plant

28. Exclusion can be accomplished by
•Separation of diseases from healthy plants
•Treating seeds with disinfectants or fumigants before
planting
•Use of certified seeds or use of seeds that has been
tested for germination
•Securing propagative materials from disease-free
sources
•Quarantine

29. Eradicative measures are exemplified by
•Killing the agent within or on the plant with
chemical disinfectants
•Killing the agent in the environment with the use of
heat as in baking the soil or using fumigants
for soil treatment
•Roguing diseased plants
•Pruning infected plant parts such as leaves, twigs,
branches
•Removal of alternate hosts of the agent such as weeds
•Crop rotation
•Fallow
•Rendering the environment unfit for the survival of the
infective agent

30. Protection is exemplified by:
•Seed treatment

•Thinning or space planting
•Pruning or trimming
•Soil of cages
•Spraying
•Elimination of vectors such as insects
•Bagging/use

31. •Seed treatment or seed dressing wherein seeds are treated or “dressed”
prior to planting
Seed Treatment equipment

32. •Pruning or trimming
a horticultural and silvicultural practice involving the selective removal of parts
of a plant, such as branches, buds, or roots.

33. •Soil drainage
refers to the soil’s natural ability to allow water to pass through it. Dense soil
will hold water, while loose soil will allow water to pass through quickly. Soil
drainage may determine which types of plants grow well in it.
•Thinning or space planting
a term used in agricultural sciences to mean the removal of some plants,
or parts of plants, to make room for the growth of others
•Elimination of vectors such as insects

34. •Bagging/use of cages
providing a barrier that will protect the plants i.e. from insects/insect vectors

35. •Spraying
sprayer is a device used to spray a liquid. In
agriculture, a sprayer is a piece of equipment
that is used to apply herbicides, pesticides,
and fertilizers on ...

36. Immunization can be accomplished by
•Selection and breeding for resistance
•Judicious application of fertilizers
•Chemotherapy

37. Methods of Plant Disease Management
1.Physical
•Heat
•Flooding
2.Cultural
• Crop rotation
• Pruning
• Trellising

38. 3.Chemical
•Drench
•Spray
•Fumigate
4.Biological
•Use of antagonists
•Use of resistant varieties
Methods of Plant Disease Management

39. DISEASES
OF
BANANA AND PINEAPPLE

40. Common name of the disease: Fusarium wilt
Causal agent: Fusarium oxysporum f.sp. cubense
Symptoms: Initial symptoms are yellowing of lower leaves, including leaf blades
and petioles. The leaves hang around the pseudostem and wither. In the
pseudostem of the diseased plant, yellowish to reddish streaks are noted with
intensification of color towards the rhizome.
Management: Severely affected plants should be uprooted and burnt. Highly
infected soil should not be replanted with banana at least for 3-4 years. Use of
disease-free planting material and resistant cultivar are recommended.
Acharya N.G. Ranga Agricultural University

41. Common name of the disease: Black sigatoka or Black Leaf Streak
Causal agent: Mycosphaerella fijiensis
Symptoms: Early symptoms appear on the lower leaves as small reddish brown
specks near the tip of lamina or near the midrib; specks grow larger
turning into spindle shapedspots with reddish brown margin and gray
center with yellow halo. Spots forming near the midrib enlarge and
extend towards the margin of lamina. Spots eventually coalesce
making the entire lamina appear dry. Disease gradually progress on the
upper leaves. Fruits are underdeveloped and ripen prematurely.
Management: Cultural practices such as improved drainage, control of weeds,
removal of diseases suckers and adopting correct spacing is
recommended. Appropriate foliar spray for controlling the pathogen.

42. Common name of the disease: Moko disease or bacterial wilt
Causal agent: Ralstonia solanacearum
Mode of dissemination: pathogen spread through infected plant parts, infested soil on
tools, machinery, hands, shoes, animals, and water run-off
Symptoms: initial stage is characterized by the yellowish discoloration of the inner leaf
lamina close to the petiole. The leaf collapses near the junction of the lamina with the
petiole. Within a week most of the leaves exhibit wilting symptoms. The presence of yellow
fingers in an otherwise green stem often indicates the presence of moko disease. The most
characteristic symptoms appear on the young suckers that have been cut once and begin
regrowth. These are blackened and stunted. The tender leaves from the suckers turn yellow
and necrotic.
Management: Early detection and destruction of the suspected plants may help in
preventing the spread of the disease. All the tools used for pruning and cutting should be
disinfected. As the insects can carry the disease causing bacterium on the male flowers,
removal of the male flowers as soon as the last female hand emerge help in minimising the
spread of the disease.
Acharya N.G. Ranga Agricultural University

43. Common name of the disease: Erwinia Rhizome rot/Soft rot/Tip over
Causal agent: Erwinia caratovora sub.sp. caratovora and Erwinia
chrysantemii
Mode of dissemination: pathogen spread through infected suckers,
infested soil, irrigation water
Symptoms: Newly planted suckers get affected, leading to rotting and emitting of
foul odour. In older plants rotting at the collar region and leaf bases are
seen. In advanced cases, trunk base becomes swollen and split.
Control: Good drainage and soil conditioning can control the disease to some
extent. Use of rhizomes with dead central buds and active lateral buds
prevents the appearance of the disease.
Acharya N.G. Ranga Agricultural University

44. Common name of the disease: Bunchy Top/Curly Top/ Cabbage
Top
Causal agent: Banana Bunchy Top Virus
Mode of dissemination: through diseased suckers, virus
particles transmitted by banana black aphid Pentalonia
nigronervosa
Symptoms: Infected suckers have narrow leaves, which are
chlorotic and exhibit mosaic symptoms. The affected
leaves are brittle with their margins rolled upwards.
Characteristic symptom of bunchy top virus is the
presence of interrupted dark green streaks along the
secondary veins of the lamina or the midrib of the petiole.
The diseased plants remain stunted and do not produce
bunch of any commercial value.
Management: Systematic eradication of the diseased plants, suckers and the
clumps is very essential. Planting materials should not be collected from
places affected by this disease. The aphid should be controlled to check
spread of the disease by spraying with appropriate insecticide. Plants
adjacent to the healthy plants should also be sprayed. The affected plant
should be killed with appropriate herbicide.The rhizome should be dug
out, cut into small sections and sprayed again so that no suckers can be
produced which may harbour the virus.
Acharya N.G. Ranga Agricultural University

45. Common name of the disease: Banana mosaic
Causal agent: Banana Mosaic Virus
Mode of dissemination: virus particles transmitted the aphid vector Aphis
gossypii
Symptoms: The disease is characterized by typical mosaic symptoms on the
leaves. Mosaic plants are easily recognized by their dwarf growth and ,
distorted leaves. The earliest symptoms appear on young leaves as light
green or yellowish streaks and bands giving a mottled appearance.
Control: The plantation should be kept free from weeds. Suckers from infected
clumps should not be used for planting. Weeds in the nearby area should
be removed as the virus survives in them during offseason. Use of
suitable insecticide to reduce spread of the disease is also suggested

47. Common name of the disease: Bacterial heart rot and Fruit collapse
Causal agent: Erwinia chrysanthemii (reassigned as Dickeya dadantii in 2005)
Symptoms: Water-soaked lesions on the white basal sections of leaves in the
central whorl which may spread to all leaves in the central whorl; midportions
of leaves become olive green in color with a bloated appearance; infected
fruits exude juices and the shell becomes olive green; cavities form within the
fruit
Mode of dissemination: through infected water, infected planting materials,
contaminated tools
Management: proper sanitation of materials, exclusion of infected materials,
and avoiding environments conducive to disease. Most important to disease
management is exclusion because D. dadantii can move through vegetatively
propagated tissues asymptomatically. Therefore, it is important to have
certified disease-free stock.
DAF, Queensland)

48. Name of the Disease: Phythophtora heart rot
Causal agent:
•Symptoms: Plants of all ages are attacked, but three to
four month old crown plantings are most susceptible.
•Fruiting plants or suckers on ratoon plants may be
affected.
•The colour of the heart leaves changes to yellow or light
coppery brown. Later,
•the heart leaves wilt (causing the leaf edges to roll under),
turn brown and eventually die.
•Once symptoms become visible, young leaves are easily pulled from the plant, and the basal
white leaf tissue at the base of the leaves becomes water-soaked and rotten with a foul smell
due to the invasion of secondary organisms.
•The growing point of the stem becomes yellowish-brown with a dark line between healthy
and diseased areas.

49. Nematodes – Rotylenchulus reniformis,
Pratylenchus brachyurus, Meloidogyne
javanica & incognita
These nematodes invade the tips of primary roots and
stop them from
elongating. The formation of root knots or galls is
typical of Meloidogyne
nematodes. Pratylenchus and Rotylenchulus create
root lesions. They
can stop root growth by burrowing through the cortex.
The last one
discolours the roots.
Plant roots infected with nematodes often become
more susceptible to
other diseases. In addition, affected plants are often
stunted.
The pineapple plants infested with nematodes present
the same
symptoms as when suffering from nutrients deficiency
and drought.

50. Common name of the disease: Black spot
Causal agent: Penicilium funiculosum and Fusarium moniliforme
Symptoms: The infection starts from one fruitlet (floral cavity) of the fruits
creating a black spot. This browning can expand up to the fruit core.
Internal browning can not be seen as long as the fruit is not cut in
cylinders.Those symptoms appear 5-6 days after the harvest
COLEACP is an international network promoting
sustainable horticultural trade.
PIP is a European cooperation programme managed by
COLEACP. It is fi nanced by the European Development
Fund and implemented at the request of the ACP (Africa,
Caribbean and Pacifi c) Group of States.
In accordance with the Millennium Development Goals,
the

51. Common name of the disease: Black rot/Stem end
rot/water blister/soft rot
Causal agent: Thielaviopsis paradoxa
Symptoms: Soft black rot which begins at the area where
the seed piece detaches from the mother plant; entire
seed piece may be rotted; black rot of fruit causes a soft,
watery rot which darkens with time; small brown, wet
spots develop on leaves; leaf spots enlarge and turn
gray-brown with light brown margins
Mode of dissemination: organism survives in the soil and
residues; organism enter through wounds
Management: seed material should be dipped in an
appropriate fungicide within 12 hours of removal from
the mother plant; avoiding bruising and wounding of
fruit during harvest helps to reduce black rot

52. Questions,
Clarifications,
Comments