Transcript Biotic Diseases

Plant diseases caused by
Bacteria
1. Spots and Blights
3. Galls
2. Soft rots
wilt
Fire blight
5. Scabs
6. Canker and Gummosis
4. Vascular wilts
Black rot
Canker and Gummosis
Wild fire
Spot
Speck
Canker
1.Bacterial spots and blights
a- Wildfire of tobacco
Disease name: Wildfire
Plant: Tobacco (Nicotiana tabacum L.)
Pathogen: Pseudomonas syringae
Symptoms:
Round spots: brown in centers and whitish yellow halos
Adjacent spots coalesce → large dead area on the leaf
b- Bacterial spot of tomato and pepper
Disease name: Bacterial spot
Plant: Tomato, Pepper
Pathogen: Xanthomonas campestris
Symptoms:
Tomato
On unripe fruits: small water soaked, slightly raised spots.
spots sometimes have greenish-white halos → dark brown with
scabby surface.
Pepper
On unripe fruits: small water soaked, slightly raised spots.
spots sometimes have greenish-white halos → dark brown with
scabby surface.
c- Bacterial speck of tomato
Disease name: Bacterial Speck
Plant: Tomato
Pathogen: Pseudomonas syringae
Symptoms:
Lesions are similar to bacterial spot but smaller
2.Bacterial vascular wilts
a- Bacterial wilt of cucurbits
Disease name: Bacterial wilt
Plant: Cucurbitaceae
Pathogen: Erwinia tracheiphila
Symptoms:
Drooping and wilting of infected leaves, which shrivel and dry
up.
Infected stems become soft and pale then shrivel (‫)ذبول‬, hard and
dry.
b- Fire blight of Pear and Apple
Disease name: Fire blight
Plant: Pear, Apple
Pathogen: Erwinia amylovora
Symptoms:
Apple
Bacterial
exudates (ooze)
from apple fruit
and stem.
Brown, black blotches
along midrib and between
veins then curl and shrivel.
Bark turns brownish black and
soft → shrinks and hardens
Pear
Brown, blak blotches
along midrib and between
veins then curl and shrivel.
Immature fruit become water
soaked, then shrivel, turn
black.
c- Black rot of crucifers
Disease name: Black rot
Plant: Crucifers
Pathogen: Xanthomonas campestris
Symptoms:
V-shaped chlorotic blotches at the
margins of the leaves → chlorosis
progress toward the midrib → affected
area turn brown and dry.
Cabbage and cauliflower heads are
discolored.
3.Bacterial soft rots
Bacterial soft rots of vegetables
Disease name: Bacterial soft rots
Plant: Vegetables ( potato, carrot,..), annual
ornamentals (iris), succulent stems, stalk or leaves
(cabbage, lettuce,..).
Pathogen: Erwinia carotovora
Symptoms:
Affected area becomes soft and mushy, the surface becomes
discolored and depressed.
Cracks develops the slimy mass exudates to the surface and
turn brown.
Cruciferous plants and onions give off repulsive odor.
A whole fruit or tuber may be
converted into a soft, watery, decay
mass within 3-5 days.
4.Bacterial galls
Disease name: Crown gall
Plant: Woody and herbaceous plants (> 60 families), mostly on
pome and stone fruit trees, brambles and grapes.
Pathogen: Agrobacterium tumefaciens
Symptoms:
Small, round, whitish soft
overgrowth on the stem
and roots (mainly near the
soil line) → the tumor
enlarge and become brown
(death
and
peripheral
decay
cells).
of
Some
tumors are spongy while
others become woody and
hard.
5.Bacterial canker and gummosis
a- Bacterial canker and gummosis of stone fruit trees
Disease name: Bacterial canker and gummosis
Plant: Stone fruit trees (apricot, pear,olive,…)
Pathogen: Pseudomonas syringae
Symptoms:
Bacterial canker:
Formation of cankers girdled the trunk or branches. Within few
week, the branch or entire tree above the canker die.
Leaves show curling and turn yellow.
Gummosis:
gum exudation
b- Citrus canker
Disease name: Citrus canker
Plant: Citrus
Pathogen: Xanthomonas axonopodis
Symptoms:
Similar lesions are on young leaves, twigs and fruits.
Small round light green spots (lesions) → they rupture and
appear corky with brown sunken centers and yellow halo.
Premature fruits drop.
6.Bacterial scabs
Common scab of potato
Disease name: Common scab
Plant: Potato, root crops (beets, radish,..)
Pathogen: Streptomyces scabies
Symptoms:
Small brownish raised spots → enlarge, coalesce and
become corky.
The lesions extend 3-4 mm deep in tuber
Plant diseases caused by
parasitic higher plants
Dodderr
Cuscuta spp.
Witchweed
Striga spp.
1.Dodder
Cuscuta spp.
Plant: alfalfa, onion, sugar beets, some ornamentals and
potato.
Parasite: Cuscuta spp.(dodder)
Symptoms:
Orange or yellow strands around the
stem and the other aboveground parts
of the plant. The parasite enter their
haustoria directly to the phloem of the
host.
During late spring and in summer,
dodder produces clusters of white,
pink or yellowish flowers.
Infected host produce poor yield and
may be killed by parasite.
2.Witchweed
Striga spp.
Plant: economic plants (corn, sugarcane, rice, cowpeas,
tobacco, small grains,..)
Parasite: Striga spp.
Symptoms:
The parasitic roots are attached
to the host ones by its root
exudates → the root haustorium
penetrates the host roots → the
haustorium reach the vessels of
the host roots, from which it
absorb water and nutrients →
infected host became stunted
and chlorotic → wilt and die