Diseases of Potato

Potato crop Diseases, Symptoms, Etiology, Disease cycle and
Their Management.
1)Early blight
2)Late blight
3)Black scurf
4)Leaf roll
5)Mosaic
6)Mild mosaic/Interveinal mosaic
7)Severe mosaic
8)Rugose mosaic of potato

1. Potato crop Diseases, Symptoms, Etiology, Disease cycle and Their Management. : Alternaria solani : Phytopthora infestans : Rhizoctonia solani : Potato leaf roll virus Early blight Late blight Black scurf Leaf roll Mosaic : Mild mosaic/Interveinal mosaic Severe mosaic Rugose mosaic of potato : (Potato virus X) PV X :Potato virus Y (PV Y) : Potato virus X &Y

2. 1. Early blight : Alternaria solani Symptoms : This is a common disease of potato occurring on the foliage at any stage of the growth and causes characteristic leaf spots and blight. Normally the disease symptoms become apparent during tuber bulking stage and develop leading to the harvest. The early blight is first observed on the plants as small, black lesions mostly on the older foliage. Spots enlarge, and by the time they are one-fourth inch in diameter or larger, concentric rings in a bull's eye pattern can be seen in the center of the diseased area. Tissue surrounding the spots may turn yellow. If high temperature and humidity occur at this time, much of the foliage is killed. Lesions on the stems are similar to those on leaves, sometimes girdling the plant if they occur near the soil line.

3. Etiology : The m y cel i u m i s s e pt a te , branched , light brow n colou r, s p rea d inter and intracelluar in the host tissue. The conodiophore are short, light brown, septate arise from disease tissue and emerge through stomata. The conidia are borne in chain at tip of conidiophores. Conidia are obclavate, muriform with 5-10 transverse septa.

4. Disease Cycle/perpetuation of Early blight of disease : Primary Infection: Mycelium or conidia in infected plant debris Secon d a ry I n f ecti o n : C on idia dis p erse d by win d, w a te r or rain splashes Management of early blight disease Use of disease free seed Practicing crop rotation helps to minimize the disease incidence. Removal and burning of diseased crop debris Nursery spraying after 2 weeks after sowing with COC 50WP [email protected]% or [email protected]% or Zineb@ 0.25% spray at weekly intervals. Spray Mancozeb + urea solution i.e. at the rate of 2 g Mancozeb 75 WP + 10 g urea per litre of water at 15 days interval when symptoms start.

5. 2. Late blight : Phytopthora infestans Symptoms : A. Symptoms on leaf The first symptoms of late blight in the field are small, light to dark green, circular to irregular-shaped water-soaked spots. These lesions usually appear first on the lower leaves. Lesions often begin to develop near the leaf tips or edges, where dew is retained the longest. During cool, moist weather, these lesions expand rapidly into large, dark brown or black lesions, often appearing greasy. Leaf lesions also frequently are surrounded by a yellow chlorotic halo The lesions are not limited by leaf veins, and as new infections occur and existing infections coalesce, entire leaves can become blighted and killed within just a few days. The lesions also may be present on petioles and stems of the plant. The lesions are not limited by leaf veins, and as new infections occur and existing infections coalesce, entire leaves can become blighted and killed within just a few days. The lesions also may be present on petioles and stems of the plant.

6. B. Symptoms on tubers: Late blight infection of tubers is characterized by irregularly shaped, slightly depressed areas that can vary considerably from brown to purplish of variable size on the skin. A tan to reddish-brown, dry, granular rot is found under the skin in the discolored areas and extending into the tuber usually less than ½ inch

7. Etiology: Mycelium is coenocytic, hyaline, branched and both inter and intracelluar The conidiophores are aerial and arise from the internal mycelium through stomata and lenticel on the tubes. They are slender hyaline, branched and indeterminate. The sporangia are thin walled, hyaline, oval or pear shaped with a definite papilla at the apex germinating by zoospore. Oospore are thick walled and yellowish.

8. Disease cycle: The i n fe c te d tu b ers a n d th e infecte d soil m ay ser v e a s a s o u r c e of primary infection. The diseased tubers are mainly responsible for persistence of the disease from crop to crop. The air borne infection is caused by the sporangia. Management : Protective spraying with mancozeb or zineb 0.2 % should be done to prevent infection of tubers. Tuber contamination is minimized if injuries are avoided at harvest time and storing of visibly infected tubers before storage. The resistant varities recommended for cultivation are Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo and Kufri Moti. Destruction of the foliage few days before harvest is beneficial and this is accomplished by spraying with suitable herbicide

9. 3 . Black scurf : Rhizoctonia solani Symptoms Symptoms can be observed on above and below ground plant parts. Symptoms observed above ground early in the season include necrosis at the tips of the sprouts (which may eventually cause the emerging plant to die) and sunken lesions on stolons, roots, and stems. Later in the season, 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.

10. Tuber russet Sunken leisons on stem Etiology : Rhizoctonia solani is a basidiomycete fungus that does not produce any asexual spores (called conidia) and only occasionally will the fungus produce sexual spores (basidiospores). In nature, R. solani reproduces asexually and exists primarily as vegetative mycelium and/or sclerotia Young mycelium of R Solani is silvery and become yellow to brown at maturity 8- 12 µm in dia. Having frequent septation and branched. Sclerotia are dark brown to black. They are roughly spherical or somewhat flattened or irregular, shape of micro scleortia is oval to irregular

11. Disease Cycle P.I: Oospores ( Pythium) or Sclerotia (Rhizoctonia) in soil S.I: Seedlings raised in infected soil carry the disease to field Management : Disease free seed tubers alone should be planted. If there is a slight infection of black scurf that can be controlled by treating seed tubers with mercuric chloride solution for 1.5 hr with acidulated mercuric chloride solution for 5 min. Treating the soil with pentachloroni trobenzene at the rate of 70 kg/ ha lowers the incidence of the disease, but it is too expensive and cumbersome. Well sprouted tubers may be planted shallow to control disease. The disease severity is reduced in the land is left fallow for 2 years.

12. 4. Leaf roll : Potato leaf roll virus Symptoms: The symptoms appear early and young leaves show an upward roll. Leaves become dry, leathery and thick. They turn brittle and give their distinctive rattle when shaken. Plants may also be severely stunted, erect and light green. Tubers are reduced in size and number. With some varieties, a net necrosis develops inside the tuber.

13. Transmission Infected tubers (Sap inoculation) Spread by aphids, Myzus persicae and Aphis gossypii Management: Disease free seed tubers for planting. Use of disease free certified seed. Rouging of diseased plants and burying them deep in soil. Aphid control.(Phorate 10 G ,10Kg/ha or monochrotophos).

14. : (Potato virus X) PV X 5. Mosaic : a. Mild mosaic/Interveinal mosaic Symptoms: Often referred as latent potato mosaic Light yellow mottling with slight crinkling on potato plants Interveinal necrosis of top foliage Stunting of diseases plants Leaves may appear slightly rugose where strains of PV Y combines

15. b) Severe mosaic – Potato virus Y (PV Y) Also called potato leaf drop streak Symptoms Chlorotic streaks on leaves which become necrotic Necrosis of leaf veins and leaf drop streak Interveinal necrosis and stem/petiole necrosis Plant remain stunted in growth Rugosity and twisting of the leaves occurs in combination with PV X and PV A

16. C. Rogose and Common Mosaic : Potato virus X &Y Symptoms Black streaks appear in leaf veins and on stems. Early-season infection shows shriveled leaves that hang from the stem by a thread of dead tissue. Later in season, the plants become bare with a few leaves on top. Late- season infection does not show any symptoms. Plants from infected seed tubers have mottled and wrinkled leaves that are distorted ("rough") and reduced. Stems are brittle and dwarfing is common. Harvested tuber size is greatly reduced. The primary pathogen is Potato Virus Y (PVY) which may act alone or in conjunction with PVX. There are many strains of PVY with differing characteristics and behaviour. PVY is spread by both seed and aphids.

17. Transmission a.) Mild mosaic/Interveinal mosaic Spreads mechanically through rubbing of leaves, contact of infected plants (Sap inoculation), seed, cutting knives, farm implements. Root clubbing of healthy and diseased plants in field b) Severe mosaic – Potato virus Y (PV Y) Infected tubers (Sap inoculation) Spread by aphids, Myzus persicae and Aphis gossypii Management: Disease free seed tubers for planting. Resistant varieties (like chippewa & Irish cobs). Use of disease free certified seed. Rouging of diseased plants and burying them deep in soil. Insect control in case of Mild and Rugose mosaic.(Phorate 10 G ,10Kg/ha) Avoid working of labour and animals from diseased to health crop in case of latent mosaic virus. Early harvesting of the crop .

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