1. Fungal diseases of vegetables-
Potato
Vaishali S.Patil
Professor, Department of Botany
Shri Shivaji College of Arts, Commerce & Science
Akola
2. 1.Black dot caused by Colletotrichum coccodes
Symptoms-The numerous dot-like, black sclerotia that can appear on
tubers, stolons, roots, and stems both above and below ground level. A
significant portion of the stem may be covered with sclerotia which are
easily seen after vine kill. Total root growth is reduced and appears
brown to black in color . Sclerotial bodies can be found on both roots and
stolons. Some of the roots and stolons appear white. Small, brownish
lesions may appear on recently infected stolons. Tuber infection appears
as brownish to gray discoloration over a large portion of the tuber or as
roundish spots. Silver scurf can also appear as patchy discoloration on
the tuber surface.
Control: Plant certified seed tubers, maintain adequate levels of
nutrients, and avoid over irrigation., crops rotation, fungicides.
3. 2.Brown spot and Black pit caused by Alternaria alternata
Symptoms- Small, brown, round spots appear on leaflets and
may have very faint concentric rings. Leaf spots coalesce
across large veins into brown blotches with dark brown
margins. Whole leaves may turn necrotic and hang dead on
plants. Leaves in the center of plants are the most susceptible.
Elongated stems cankers can develop under high disease
pressure. Small, deep black pits can develop on tubers when
infected during harvest.
Control: Crop rotation fungicides.
4. 3.Cercospora leaf blotch caused by Mycovellosiella concors
Cercospora solani, Cercospora solani-tuberosi
Symptoms- Round or angular brown spots with green, brown,
gray or white centers appear on leaves. The leaves eventually
die and the whole plant can become defoliated.
Control: Eliminating infected plants, volunteers and weeds.
Give plants plenty of water and nutrients, good air circulation
and well-drained soil, rotate crops, treating seeds with hot
water,fungicides.
5. 4.Charcoal rot caused by Macrophomina phaseolina
Symptoms- Foliage of affected plants wilts and turns yellow,
infected stems develop a soft, dark rot, affected stems take on
a dusty black appearance when small, black fungal structures
(microsclerotia) are formed. Shallow, water-soaked lesions
develop on tuber. Tuber tissue within these lesions turns gray,
and eventually the lesion tissue becomes filled with black
fungal mycelium. Tuber tissue may develop a soft rot that
turns from white to pink and then black.
Control: Plant certified seed tubers, early-season cultivars,
harvest as soon as tubers have matured, avoid injuring tubers
during harvest, rotation to nonhost crops.
6. 5.Choanephora blight caused by Choanephora
cucurbitarum
Symptoms- Host tissues have a hairy appearance resulting
from the tall sporangiophores that produce a cluster of brown
sporangiola (often referred to as conidia) at their tips. Dark
brown and soft-rotted lesions appear on young flower stalks,
and the stalks and flowers become covered with luxuriant
metallic, clustered sporangiophores. water-soaked lesions
devolope at the leaf margins and tips. These lesions became
dry and turned olive-green to light brown.
Control: Fungicides, bioagents, resistance varieties.
7. 6.Common rust caused by Puccinia pittieriana
Symptoms-Lesions begin as minute, round, greenish-white spots on the
underside of leaves. Some lesions become elongated with their longer
axes. They later become cream, with reddish centres that turn tomato-red
and finally rusty-red to coffee-brown. The lesions protrude with
corresponding depressions on the upper leaf surface, and may be
surrounded by chlorotic or necrotic halos. Defoliation results when
hundreds of lesions form on a leaf. Elongated or irregular lesions occur
on petioles and stems; fruits and flowers are also affected.
Control: Fungicides, use of resistance variety.
8. 7.Deforming rust caused by Aecidium cantensis
Symptoms- saucer-shaped aecia and growth distortions of the
leaves and stems
Control: fungicides, Good field drainage and proper plant
spacing, Infected vines can be destroyed by herbicide or
burning.
9. 8.Early blight caused by Alternaria solani
Symptoms- leaves appear as small black or brown lesions and under conducive
environmental conditions the lesions will enlarge and are often surrounded by a yellow
halo . Lesions often have dark pigmented concentric rings. This so-called “bullseye”
type lesion is highly characteristic of early blight. As lesions expand and new lesions
develop entire leaves may turn chlorotic and dehisce, leading to significant
defoliation. Lesions occurring on stems are often sunken and lens-shaped with a light
center, and have the typical concentric rings.The tubers are characterized by sunken,
irregular lesions , which are often surrounded by a raised purple border. Beneath the
surface of the lesion the tuber tissue is leathery or corky with a brown
discoloration. Early blight lesions on tubers tend to be dry and are less prone to
invasion by secondary organisms than lesions of other tuber rots. After prolonged
storage severely diseased tubers may become shriveled.
Control: field sanitation ,crop rotating , careful handling tuber, avoiding harvesting
during wet conditions, Tubers should be stored at 50 to 55 F, at high relative humidity
and with plenty of aeration , Avoid irrigation in cool, cloudy periods or late in evening ,
Selecting fields with good drainage , Resistant varietes, Fungicides .
10. 9.Fusarium dry rot caused by Fusarium spp.
Symptoms- A dry rot of the tuber starts from a wound or bruise and is at
first small and brown. Mold on the rotting tuber may be white, rose, or
violet. As the rot progresses, a cavity begins to form, the tuber
mummifies and ultimately only the dry shell persists.
Lesions start at the side of the infection and progress in a fairly uniform
manner through the tuber. As lesions age, rots turn yellow to brown.
Lesions tend to be very dark brown to black and progress through the
tuber in a very irregular manner sometimes called "tunneling."
Control: Tubers must be mature and skins are well "set" before
harvest,avoid wounding and bruising tubers by handling carefully,
harvest during dry, cool weather, fungicides, biological control.
11. 10.Gangrene caused by Phoma solanicola f. Foveata,
Phoma exigua var. Exigua
Symptoms-Black pycnidia may appear at the base of the
stems at the end of the growing season or even later, after
haulm destruction.Dark depressed areas may be observed on
tubers, characterised by thumb mark spots which are
frequently found around the wounds, the eyes, the lenticels or
at the heel-end. Wrinkles tend to stretch across rather than the
concentric rings expected with dry rots.
Control: Limiting handling damage, earlier harvesting and
dry curing, fungicides.
12. 11.Gray mold caused by Botrytis cinerea, Botryotinia
fuckeliana
Symptoms- first observed on flowers as gray, fuzzy growth.
As flowers drop into the foliage, lesion may develop on
leaves, appearing as tan, wedge-shaped lesions largely
confined by plant veins. Stems often develop a brown, slimy
rot when leaf infections progress through petioles.
Control: fungicide, remove crop debris
13. 12.Late blight caused by Phytophthora infestans
Symptoms- water-soaked spots appear usually at the tips or edges of
lower leaves where water or dew tends to collect. Water-soaked spots
rapidly enlarge and a broad yellow halo may be seen surrounding the
lesion. On the leaf underside, a spore-producing zone of white moldy
growth may appear at the border of the lesion. Tuber lesions first appear
as irregular, dark blotches. When cut open, affected tissue is water-
soaked, reddish brown and extends with an irregular margin into the
tuber flesh. Lesions may start as a superficial decay. Older lesions may
become firm and sunken due to water loss and tubers will appear
shrivelled.
Control: fungicide, resistant varieties
14. 13.Leak / water rot caused by Pythium spp.
Symptoms-Spongy, wet internal rot of tubers. The diseased
flesh is clearly demarcated from healthy tissue by a dark
boundary line. In advanced infections, hollow cavities form
and all that remains of some infected tubers are tuber shells
with thin papery skins.
Control: Avoid overwatering near harvest. Allow tubers to
mature completely before harvest. Minimize bruising the
tubers. In areas where leak is a problem, apply fungicide
15. 14.Fusarium wilt caused by Fusarium spp.
Symptoms- Lower leaves of infected plants turn yellow and
wilt. Leaf tissue between veins turns yellow then brown.
Wilting and yellowing of foliage progresses up the stems of
affected plants. Vascular tissue in stems and tubers often
develops a brown discoloration; typically there is a stem end
rot of the tubers.
Control: Plant disease-free seed tubers. Avoid growing seed
potatoes in ground known to be infested with the Fusarium
wilt pathogen. Rotation out of potatoes or other solanaceous
crops.
16. 15.Phoma leaf spot caused by Phoma andigena var. Andina
Symptoms- Small blackish lesions develop on leaves. Leaf
spots appear first on lower leaves, later on the whole plant.
Coalescence of lesions may occur, with large lesions delimited
by leaf veins. Leaves turn black as if scorched. Initially
remaining attached, they later drop. Elongate lesions develop
on petioles and stems. The ostioles of pale conidiomata
emerge through the upper epidermis.
Control: fungicides, resistance varieties.
17. 16.Pink rot caused by Phytophthora spp.
Symptoms- On the outside of the tuber, a dark line delineating the
margin of decay. When the tuber is cut and exposed to air, infected
tissues change from cream-colored to salmon-pink and then black.
Tubers with pink rot have a rubbery texture and give off an ammonia
odor.
Control: Select fields that have no history of pink rot, crop rotation,
avoid excessive soil moisture, avoid conditions that favour disease
development and spread during harvest. Don’t harvest when tuber pulp
temperatures are above 65°F. Avoid bruising or wounding tubers during
harvest. Remove pink rot tubers while loading potatoes into storage.
Reduce tuber pulp temperatures to 50°F.Avoid water condensation. Do
not expose cold tubers to warm air, fungicides.
18. 17.Powdery mildew caused by Erysiphe cichoracearum
Symptoms- brown lesions of various sizes on stems and
petioles. Lesions coalesce to form short streaks or stippled
patches. Leaves and stems are killed, and only the tip of the
plant may remain green. In severe cases, vines collapse.
Infection and vine collapse may be over large areas of the
field. Small black specks may develop in the powdery growth.
Control: early planting, resistance varieties.
19. 18.Powdery scab caused by Spongospora subterranea f.sp.
Subterranea
Symptoms- Roots can develop distinctive light coloured irregularly
lobed galls. Powdery scabs first show as small raised pimples beneath
the skin. As they expand, the skin breaks open to expose a dark brown
powdery mass of cystosori. The lesions are usually shallow depressions
surrounded by raised torn edges of ruptured skin. They are generally
small, dark and round. Cystosori under the skin can give the scab a dark
margin.Where large areas are affected, powdery scabs tend to appear as
grouped individuals and generally do not coalesce into giant scabs.
Another form of the disease occurs where eye infections result in
prominent outgrowths (cankers), often covered in brown pitted
depressions but without ragged skin edges.
Control: resistance varieties, crop rotation, do not over-irrigated,
fungicides.
20. 19.Rhizoctonia canker and black scurf caused by Rhizoctonia solani,
Thanatephorus cucumeris
Symptoms- Sunken lesions on stolons, roots, and stems, sclerotia are
produced in the tubers creating a sign called black scurf which is simply,
sclerotized mycelium. Stems with cankers can become girdled, resulting
in stunted plants. Leaves of infected plants develop a purplish and
chlorotic coloration. In severe infections, green tubers develop above the
ground. Affected tubers are deformed and can produce sclerotia on the
surface .
Control: Use disease-free soil, Conduct a soil test, Use certified potato
seed, long rotations, Separate tubers from crop residues after destruction
of the stem, resistant varieties, fungicide.
21. 20.Rosellinia black rot caused by Rosellinia sp.
Dematophora sp.
Symptoms- Mycelial inoculum of the dormancy stage
encounters roots, mycelial masses and strands start to
propagate on the roots, penetrate from the lenticels of
epidermal cells and junctions between epidermal cells, and
then invade the epidermis and xylem of the roots, forming fan-
shaped mycelial strands.
Control: disease resistance varieties, fungicide, hot water
treatment.
22. 21.Septoria leaf spot caused by Septoria lycopersici var.
Malagutii
Symptoms- The spots may become gray or tan in the center,
with dark brown borders. As the spots mature, they may grow
a dark brown, pimple-like fungus inside of the spots.
Eventually the leaf turns yellow and then dies.
Control: fungicide
23. 22.Silver scurf caused by Helminthosporium solani
Symptoms- Symptoms usually appear at the stolon end of the tuber as
small pale brown spots. Severe browning of the surface layers of tubers
may occur, followed by sloughing-off of the outer layers of the
periderm. Lesions have definite margins and are circular, but individual
lesions may coalesce as the disease progresses. The silvery appearance of
older lesions. The surface of the infected tubers may become shriveled
and wrinkled due to excessive water loss from the silver scurf lesions.
Cell death, however, never extends beyond the periderm into the tuber
flesh.
Control: Early harvest of tubers, manipulation of storage conditions,
use of uninfected seed, control of volunteers, crop rotation, appropriate
fungicide, seed treatments and resistant varieties.
24. 23.Skin spot caused by Polyscytalum pustulans
Symptoms- On stems, small shallow light brown lesions coalesce into
larger brown patches and deep longitudinal cracks develop. Stems might
also become brittle and show stress fracturing. Skin spots on tubers tend
to be dark grey and slightly raised. The mature fungal lesion frequently
forms a sunken ring around a raised centre. Lesions may form either
singly or in clumps and be distributed at random or aggregated around
eyes, stolons and damaged skin. Cutting through a skin spot shows a
dark thickening on the tuber. Tubers incubated in a moist container for 3
days at room temperature may develop sporulating mycelia, visible as
white fluff.
Control: long rotations, Disease-free seed Stores should be
cleaned and disinfected.
25. 24.Stem rot (southern blight) /White mold caused by
Sclerotium rolfsii, Sclerotinia sclerotiorum ,Athelia rolfsii
Symptoms- infects lower stems near or at the soil surface, but
it also may infect any part of a susceptible plant, wilting takes
place. Wilted plants often decline and die rapidly as a result of
an extensive lower stem rot.
Control: plant removal, soil removal or treatment, plant
treatment, crop rotation, use of resistant varieties, or a
combination, fungicides.
26. 25.Thecaphora smut caused by Angiosorus solani
Symptoms- Infected tubers are misshapen or have warty swellings on
the surface, and are hard. The whole or only part of the tuber may be
infected. Numerous brown-black specks, interspersed with lighter-brown
specks, can be seen in the flesh. The specks (spore sori) are filled with
rusty brown spore balls. Completely infected tubers later become dry
brown powdery masses of numerous spores. Galls resembling deformed
tubers develop on the stems or stolons underground, often encircling
them.
Control: planting of smut-free seed potatoes, long crop rotations,
elimination of the weed, use of resistant cultivars
27. 26.Ulocladium blight caused by Ulocladium atrum
Symptoms- Pale centres or uniformly black surrounded by
alternating concentric rings of dark and pale necrotic tissues
fond on leaves. It also causes rot of stems and spikes.
Control: Fungicides
28. 27.Verticillium wilt caused by Verticillium albo-atrum, Verticillium
dahliae
Symptoms- the top leaves first, causing them to turn yellow and
eventually die. The entire stem dies quickly. More typically, the lower
leaves turn yellow and eventually die. The stem tends to remain erect
rather than flopping over when it dies. The stem xylem becomes yellow
and then turns a reddish-brown color. The color often extends through
the entire stem and into the tuber. The vascular ring of stem may have
brown or black discoloration.
Control: resistant varieties, high quality seed, avoid repeated planting,
crop rotation, seed treatments.
29. 29.Wart Synchytrium endobioticum
Symptoms-Galls produced on several plant parts. These galls
are primarily parenchymatous and may form on stem tissue,
including the stem base, stolon buds, and tuber eyes. Galls
most often form on below-ground portions of the plant. Galls
also occasionally form on the upper stem, leaf, or flower. Galls
will vary in shape but are mostly spherical outgrowths.
Aboveground galls are green to brown, turning black at
maturity, and are prone to decay. Belowground galls are white
to brown and turn black as they decay
Control: Resistant plants.
