Transcript PLANT DISEASE

PLANT DISEASE
Definition
“a series of visible and invisible responses
of plant cells and tissues to a pathogenic
microorganism or environmental factors
that result in adverse changes in the form
,function , or integrity of the plant and may
lead to partial impairment or death of the
plant
or
its
parts”
CAUSES OF PLANT DISEASE
1. Living (animate)
2. Non- Living (inanimate)
CLASSIFICATION OF PLANT DISEASE
1. on the basis of extent to which diseases are associated with plant :
a) Localised diseases
b) Systemic diseases
2. on the basis of mode of primary infection :
a) Soil-borne diseases
b) Air – borne diseases
c) Seed- borne diseases
3. on the basis of kind of symptoms :
a) Rust b) Smut c) Mildews d) Root- dots e) Blights
f) leaf spots g) Wilts h) Cankers i) fruit – rots and etc…
Disease Caused By Fungi
1)DOWNY MILDEWS
Downy mildew refers to any of several types
of oomycete microbes that are obligate parasites of plants.
Downy mildews exclusively belong to Peronosporaceae.
Development and severity depend greatly on the presence of a
film of water on the plant tissue and on high humidity in air
during cool or warm periods.
Bordeaux – 1st Fungicide
It may destroy 40-90% of young plant heavy losses of crop
yield .
Downy Mildew Of Grapes ( Vitis vinifera)
Symptomatology:
# small ,pale yellow ,irregular spot on upper surface of leaf.
# downy growth of the sporangiosphore of the fungus appear on
the underside of spots. White downy spore masses on the
lower surface of the leaf.
#Later, infected leaf areas are killed and turn brown ; spots
often enlarge, unite or combine to form large dead areas and
finally result to defoliation.
#
#berries become leathery ,distorted ,thickened , wrinkled and may
die .
#Downy mildew rapidly kills highly susceptible
young bunches , but berries are immune well before
pea-size.
Etiology :
Caused by Plasmopara viticola.
Control:
*sanitation
*use of Resistant Varieties (Several North American species
show resistance to downy mildew (e.g. V. labrusca and
V. rotundifolia) ) .
*Fungicidal Sprays – Bordeaux, Zineb & Mineb(0.2%), Captan (0.20.5%),Metalaxyl with Copper Oxychloride(0.3%).
*Automatic weather stations (AWS) monitor the vine canopy for leaf
wetness, rainfall, relative humidity and temperature, critical to downy
mildew.
Downy Mildew Of Bajra
Symptomatology:
# the infected plants are dwarfed because of shortening of
internodes & tillering is excessive.
# the foliage become pale & chlorotic & on the underside covered
by sporangia. Leaves become distorted and wrinkled .
#the whole inflorescence reduced and converted into leafy bearded
structure without bearing any grains.
Etiology:
Causal organism of Downy mildew of Bajra
Sclerospora graminicola
Control:
# Seed Treatment : hot water treatment or treatment with Cresan &
Agrosan GN.
# Resistant Varieties .
# crop rotation & avoidance of water logging will reduce the primary
inoculums.
2) Fungal Wilt.
*A wilt disease is any number of disease that affect the vascular
system of plants. Vascular wilts are widespread, very destructive ,
spectacular and frightening plant disease .
*which characterized by rapid wilting, browning and dying of leaves
and succulent shoots of plant followed by death of the whole plant.
*the infected plant loose turgidity, become flaccid and light green to
yellow , droop , finally wilt brown  die.
*xylem vessel may be clogged with mycelium ,spores or
polysaccharides produced by fungus. Clogging is further increased
by gels and gums formed by accumulation and oxidation of
breakdown products of plant cells attacked by fungal enzymes.
*fungus in leaves cause reduced chlorophyll synthesis along the vein
(vein clearing) and reduced photosynthesis, disrupt the
permeability of the leaf cell membranes and their ability to control
water loss through transpiration , and thereby result in leaf
epinasty ,wilting , interveinal necrosis , browning and finally death.
Fusarium Wilt :
*Fusarium wilt is a common vascular wilt fungal disease, exhibiting
symptoms similar to Verticillium wilt . The pathogen that causes
Fusarium wilt is Fusarium oxysporum .
*F. oxysporum is a common soil saprophyte that infects a wide host
range of plant species around the world. Development of the
disease is favored by high temperatures and warm moist soils.
*The fungal pathogen Fusarium oxysporum affects a wide variety of
hosts of any age. Tomato, tobacco, legumes, cucurbits, sweet
potatoes and banana are a few of the most susceptible plants, but
it will also infect other herbaceous plants.
*Fusarium oxysporum generally produces symptoms such as wilting,
chlorosis, necrosis, premature leaf drop, browning of the vascular
system, stunting, and damping-off. The most important of these is
vascular wilt. On older plants, symptoms are more distinct
between the blossoming and fruit maturation stages.
Fusarium Wilt Of Tomato :
Symptomatology :
# slight vein clearing on outer leaflets and drooping of leaf
petioles.
# leaves Epinasty caused by drooping of Petioles.
# Later the lower leaves wilt, turn yellow and die and the entire
plant may be killed, often before the plant reaches maturity.
Wilting of leaves , marginal necrosis , brown streaks, defoliation.
# yellowing of the foliage, beginning with the lower leaves and
working upward. Yellowing often begins on one side of the vine.
Infected leaves later show downward curling, followed by
browning and drying.
# In many cases a single shoot wilts before the rest of the plant
shows symptoms or one side of the plant is affected first .Main stem
is cut, dark, chocolate-brown streaks may be seen running
lengthwise through the stem.
#This discoloration often extends upward for some distance and is
especially evident at the point where the petioles joins the stem.
Vascular browning can be seen in infected stems and large leaf
petioles.
# root systems are stunted. The degree of stunting depends upon
time of root infection and in some cases adventitious roots are
formed.
Etiology:
Fusarium oxysporum f. sp. lycopersici
The pathogen is soil borne and persists for many years in the soil
without a host. Most infections originate from the fungus
associated with infected tomato debris.
Control :
# Use of Resistant Varieties ( Amelia , BHN-444, Carolina gold,
Empire, Florida 47, Floralina , Mountain pride , etc….)
# Soil sterilization .
# hot water treatment to seeds.
# Solar heating .
3) Bacterial Blight of Rice :
Damage is due to partial or complete blighting of the leaves or due to
complete wilting of the affected tillers leading to unfilled grains.
This disease known since 1881 in Japan , become quite severe in
India since 15 years.
In leaf blight disease, the spots enlarge in size, rapidly necrotic, and
through combine of several small spots, may produce large dead
areas of various shapes.
Bacterium induce either wilting of plant or leaf blight .Wilting
syndrome known as ‘Kresek’ occurs sporadically in the field
causing serious damage.
Bacterial blight commonly occur within 3-4 weeks after
transplantation of crop. Bacterial blight of rice causes annual
losses as high as 60%.
Symptomatology :
# Linear yellow to straw colored stripes with wavy margin developed
usually on both the edges of the leaf. The stripes usually develop
from the tip towards the base  dry rapidly  wither.
# Spots formed on leaf sheath combine to form straw brown large
lesions.
# Bacterial ooze, pale amber in color, is found on the affected
portions. On drying, these drops make crust and make the leaf
surface rough.
# As disease advances, the lesions cover the entire blade, turn white
& later become grayish due to the growth of saprophytic fungi.
# wilt affected tillers leading to unfilled grains.
Etiology:
Xanthomonas campestris pathovar oryzae
Gram –ve rod , 0.5 – 1.0 micron ,non – sporing with a single polar
flagella, aerobic and TDP – 53 degree Celsius .
On N.A , colonies are tiny , circular & bright yellow.
The pathogen may survive on crop debris in soil. The bacterium is
carried over through infected seeds.
Rainy weather , strong wind and temperature of 22-26 C favor the
rapid spread of disease in the field.