Fungal diseases of vegetables potato

Fungal diseases of vegetables-Potato

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: F ungicides

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.