4. early and late blight of potato tomato and potato scab.pptx

early blight

1. Late blight of Potato & T omato

2. Caused by: Phytophthora infestans

3. Etiology

4. Symptomatology Initially starts from leaf tips or margins and spread inward Small faded green patches on upper surface of leaf which turn into brown spots Downy growth of the pathogen on subsequent lower surface Progressive defoliation and collapse of plants under favourable conditions Water soaked stripes on stem which becomes necrotic Purplish brown spots appear on skin of tubers On cutting, the affected tubers show rusty brown necrosis spreading from surface to the centre Decay of plant parts under favourable weather which emits foul smell

5. Water soaked spots Rusty brown tuber Infected field White growth

6. Epidemiology Cool moist conditions favour the disease spread while dry spells kill the fungus quickly. Relative humidity >90% coupled with suitable temperature 12- 24 is most important for disease development The sporangia germinate at temperature ranging from 2- 30 Temperature around 16-18 are optimum for mycelial growth while 9-16 are optimum for sporulation At a temperature 12-13, the sporangia germinates by producing zoospores while direct germination of sporangia takes place around 24 Dutch rules Night temperature below the dew point for at least 4 hours Minimum temperature of 10°C Cloudiness on the next day. Rainfall at least 0.1 mm on the following day Forecasting of disease

7. Disease cycle

8. Disease cycle

9. Management practices Use of disease free seed materials Field sanitation- removal of infected crop debris, weed host Rotations of two to three years to non-host crops are recommended to control late blight. Hilling of potatoes increases the amount of soil between tubers and the soil surface and thus helps protect tubers from sporangia that land on the soil surface. Proper plant spacing reduces the incidence of blight. Avoid overhead irrigation. Avoid excess use of nitrogen fertilizer. Use of disease resistant varieties- Ex: Janakdev, Khumal Ujjwal, Khumal Upahar and so on. Escape disease by adjusting planting time. As a protectant, Spray Mancozeb @2.5 g/ l of water in 7-10 days interval for 2-3 times. Spraying of Sectin- 60 WG ( Fenamidone 10% + Mancozeb 50%) @ 2 g/ l of water or Dimethomorph 50 wp @ 2g/l of water in 10 days intervals.

10. Early blight of Tomato & Potato Early blight is one of the most common tomato diseases, occurring nearly every season wherever tomatoes are grown. It affects leaves, fruits and stems and can be severely yield limiting when susceptible cultivars are used and weather is favorable. Severe defoliation can occur and result in sunscald on the fruit. Early blight is common in both field and high tunnel tomato production.

11. Etiology Caused by Alternaria solani & A.tomatophila Toxin: Alternaric acid Conidiophores arising singly or in small groups, pale brown to olivaceous-brown, up to 110 µm long, 6–10 µm thick, with one or more distinct conidial scars. Conidia usually single, rarely in short chains, straight or slightly curved, obclavate and tapering to a beak, which may be longer than body of conidium, overall length 150–300 µm, 15–19 µm wide, pale golden or olivaceous brown, beak pale coloured, sometimes branched. 9–11 transverse septa, 2- 3 longitudinal or oblique septa;

12. Symptoms On leaves Initially, small dark spots form on older foliage near the ground. Leaf spots are round, brown and can grow up to half inch in diameter. Larger spots have target- like concentric rings. The tissue around spots often turns yellow. Severely infected leaves turn brown and fall off, or dead, dried leaves may cling to the stem.

13. On stem Seedling stems are infected at or just above the soil line. The stem turns brown, sunken and dry (collar rot). If the infection girdles the stem, the seedling wilts and dies. Stem infections on older plants are oval to irregular, dry brown areas with dark brown concentric rings.

14. On Fruits Fruit can be infected at any stage of maturity. Fruit spots are leathery and black, with raised concentric ridges. They generally occur near the stem. Infected fruit may drop from the plant.

15. Disease cycle & Epidemiology The fungus overwinters as mycelium or spores in the infected plant debris Primary infection occurs on older leaves early in the season In general hot & humid climate with frequent rains is favourable for disease development Disease develops at moderate to warm 15-26°C temperatures; 27- 30°C is optimum. Rainy weather or heavy dew, 90% humidity or greater Spores can germinate between 8-32°C and need free water or humidity of 90% or greater. Spores can be spread throughout a field by wind, human contact or equipment, resulting in many reinfection opportunities throughout a growing season.

16. Management practices Use pathogen- free seed, or collect seed only from disease- free plants. Rotate out of tomatoes/potatoes and related crops for at least two years. Fertilize properly to maintain vigorous plant growth. Particularly, do not over- fertilize with potassium and maintain adequate levels of both nitrogen and phosphorus. Avoid working in plants when they are wet from rain, irrigation, or dew. Use drip irrigation instead of overhead irrigation to keep foliage dry. Stake the plants to increase airflow around the plant and facilitate drying. Staking will also reduce contact between the leaves and spore- contaminated soil. Apply plastic or organic mulch to reduce humidity and provide a barrier between contaminated soil and leaves. In the fall, remove or bury infected plants to reduce the likelihood of the pathogen surviving to the following year. With the initiation of the disease, spray the crop with Mancozeb (0.25%) or Chlorothalonil (0.2%)

17. Potato wart (Etiology, Symptoms, Epidemiology, Disease cycle and Management Practices)

18. Introduction Also called black scab, black wart, cauliflower disease, potato tumor, potato cancer, potato canker ,wart, warty disease (Frank ,2007) Originated in the Andean zone of South America. The most important world- wide quarantine pathogen of cultivated potato. Occurrence : Asia, Africa, Oceania, Europe, South- America and North America (Smith et al . 1997) Yield losses in the range of 50-100% (Hampson ,1993; Melnik, 1998) Primitive fungus characterized by the lack of hyphae, the formation of zoospores and the development of long- lived resting sporangia.

19. Thallus- Unicellular, endobiotic and holocarpic Asexual reproduction: Zoospores produced in zoosporangia Zoospores are pear shaped with posteriorly uniflagellate whiplash type . Resting sporangia are golden brown and spheroidal (35 to 80 µm in diameter). Sexual reproduction: Isogamous planogametic copulation Fig: Ultrastructure of S. endobioticum resting spores

20. Symptoms Symptoms in the field Leaf symptoms Symptoms on stem base Symptoms on tubers and stolons Symptoms on tuber

21. Symptoms Symptoms usually appear only on tubers and stolons or underground stems, therefore the disease is often not noticed until the tubers are lifted. On infected tubers, the eyes develop into characteristic warty, cauliflower-like swellings. When formed underground, they are the same colour as the potato skin, but gradually darken with age. If exposed to light, they turn green. Tubers may bear more than one warty outgrowth and, in some cases, the whole tuber can be affected. When infected early, tubers can become distorted and spongy. Young potato warts are white in color and soft and pulpy in texture. They darken and decay as they become mature

22. Disease cycle & Epidemiology The resting sporangia are released into the soil on disintegration of warty structures where they can remain dormant for several years. When soil becomes wet after irrigation or rainfall in the next spring, these resting sporangia germinate and cause fresh infection For germination of resting spores & sporangia, a film of water is necessary. Infection can occur at temperature ranging from 10-27°C & at soil pH ranging from 4- 8.6 Optimum temperature for infection is 21°C. Annual precipitation: 70 cm

23. Disease cycle

24. Management practices Quarantine check Selection of healthy tuber from disease free site. Use disease resistant varieties like Cardinal, Khumal white- 1, khumal red- 2, N.P.I- 106, Janakdev. Intercropping potato with maize. Crop rotation for at least 5 yrs years with maize or wheat has been found to reduce the population. Infected tuber or debris should be burned or buried deeply. Thiobacillus thiooxydans as a biological control Soil fumigation with formalin 5%.

25. d. Common Scab

26. Caused by: Streptomyces scabis

27. Symptoms Corkiness of the tuber periderm is the characteristics symptoms. 1/4 inch into the tuber surface have rossette appearance. The infected tuber is slightly pitted. Light brown to dark brown lesion appears on the infected tuber. Affected tissue will attract insects which result in further attack by insects.

28. Disease cycle and epidemiology   The bacterium from Streptomyces is spread by spores on seed, in the soil, in soil water and can hitch a ride on nematodes or insects. The spores enter the tubers through wounds and lenticels. Young lenticel provide entry. Once in the plant, Streptomyces scabies produces a phytotoxin that breaks down cell walls and penetrates rapidly growing cells. As the potato plant cells die, they produce cork cells that push outward and form a scab lesion. As these cork cells continue to develop, the lesions grow larger. The type of scab (raised, superficial or pitted) varies based on the potato cultivar, environment and soil microbial community.

29. Management Plant only scab free seed potatoes as this help in checking the spread of the inoculum and infection to be subsequent crop. Green manuring the fields before planting potatoes can effectively reduce the disease incidence. Common scab is severe in alkaline soil and application of alkaline fertilizers like calcium ammonium nitrate should be avoided. Remove infection of the seed tubers by practicing 1.5hrs dip in mercuric chloride 0.1% solution or by 2h dip in 1 part formaldehyde in 240 parts of water. This disease can be reduced by soil application of PCNB at the time of planting.

30. Other diseases of potato Brown rot or Bangle blight - caused by Ralstonia solanacearum Black scurf- Rhizoctonia solani Sclerotium rot- Sclerotium rolfsii Bacterium wilt- Ralstonia solanacerum Wilt diseases- Fusarium sp. And Verticillium sp .