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Casual organisms: symptoms, life cycles and control of plant diseases
- 1. BOTANY ISA-1 Casual organism,symptoms and control of Plant diseases OCTOBER 15, 2020 WINONA MARIA CARVALHO FY, BSc in Biotechnology
- 2. Favourable conditions: ▪ Temperaturesof less than 18°C (optimum 6- 12°C) with a minimum of three hours of leaf- wetness (for example, dew). ▪ Once an infection is established within the leaf the fungus can survive short periods of temperatures as high as 40°C. Yellow stripes, raised pustules appear on the leaves, especially on the older leaves lying low in the canopy and can be easily wiped off onto a white cloth or tissue leaving a yellow stain. Alternate hosts: ▪ Agropyron ▪ Bromus Yellow rust Disease: Stripe rust (Yellow rust) Causal organism: Puccinia striiformis
- 3. ❑ Symptoms ❑Yellow stripesof pustules appear on the leaves, especially on the older leaves lying low in the canopy. ❑ These pustules are raised above the leaf surface and can be easily wiped off onto a white cloth or tissue leaving a yellow stain. ❑ Hot spots are 1-10 meters in diameter and are generally well developed just before the disease becomes widespread in the crop.
- 4. Disease cycle ofstripe rust
- 5. Stripe rust iscaused by the fungus Puccinia striiformis. Stripe rust survives from one season to the next predominantly on volunteer self-sown cereals, but can also survive to a lesser extent on other cereal and grass weeds that grow over summer. Stripe rust epidemics are usually more severe in seasons following wet summers that have supported the ‘green bridge. During the season, conditions suitable for epidemic and stripe rust can be expected in crops by January to April in the years. For an infection of a plant to occur the spore requires temperatures of less than 18°C (optimum 6- 12°C) with a minimum of three hours of leaf-wetness (for example, dew). Once an infection is established within the leaf the fungus can survive short periods of temperatures as high as 40°C. Following infection of the leaf the fungus grows within the leaf for 14 to 28 days (or longer depending on temperature) until the spores appear on the leaf surface as pustules. The time between infection and symptom development is known as the latent period, with the time reducing as temperatures warm during the spring. The spores are then dispersed by wind, allowing the cycle to repeat multiple times during the season.
- 6. The Green Bridge Striperust can only survive from one season to the next on living plants: mostly wheat and to a lesser extent barley, triticale, barley grass, brome grass and phalaris. This is called the ‘green bridge’. Stripe rust does not survive on seed, stubble or soil. Therefore, the greater the number of susceptible volunteer wheat plants growing during summer/ autumn the greater the risk of a stripe rust epidemic and the reason that stripe rust is often more severe following wet summers. The susceptibility of the volunteer wheat plants over summer influences the quantity of inoculum generated by the green bridge. If most varieties in a district are resistant there will be considerably less inoculum than if many plants are susceptible or very susceptible.
- 7. Management Strategies toMinimize the Impact of Stripe Rust The following management strategies are recommended to minimize the impact of stripe rust: ▪ Remove volunteer wheat plants (the ‘green bridge’) that will support stripe rust inoculum in the 6 weeks prior to sowing ▪ Avoid Very Susceptible (VS) and Susceptible (S) varieties by selecting more resistant varieties ▪ Use a seed or fertilizer treatment to suppress early infection ▪ Monitor crops during the growing season and apply a foliar fungicide early in the epidemic, if required. Spray. (azoxystrobin + propiconazole)/ (Tebuconazole+ Trifloxystrobin)/ azoxystrobin/ (azoxystrobin + tebuconazole) 0.2% at 7 to 10 days from flag leaf emergence to early dough grain development stage or at earliest sign of rust pustules development.
- 8. Brown or orangerust Disease: leaf rust (Brown or orange rust) Causal organism: Puccinia triticina (formally Puccinia recondita) Favourable conditions: ▪ Wet conditions and ▪ Temperatures of approximately 15-22°C Circular to oval, orange-brown pustules appear scattered across the leaf surface that are raised above the leaf surface and these pustules are confined chiefly to the upper surface of the leaf.
- 9. ❑Symptoms of leafrust ▪ Circular to oval, orange-brown pustules appear scattered across the leaf surface that are raised above the leaf surface and these pustules are confined chiefly to the upper surface of the leaf. ▪ Later in the season, black teliospores develop on mature plants, usually on the under surface of the leaf or on the leaf sheath.
- 10. Teliospores play an importantrole by either infecting volunteer wheat plants or barberry plants Secondary cycles Disease cycle of leaf rust
- 11. ▪ Leaf rustis caused by the fungus Puccinia triticina (formally Puccinia recondita). Leaf rust, like other cereal rusts, requires a living host to survive from one season to the next. ▪ The most important hosts for rusts are susceptible volunteer plants such as weeds, wheat plants growing during the summer/autumn. Rust cannot carry over from one season to the next on seed, stubble or soil. ▪ Wheat varieties susceptible to leaf rust enable inoculum levels to build up on volunteers during the summer and autumn. This can be a problem in seasons following wet summers that favour the growth of self-sown wheat. The plants that become heavily infected with rust in the autumn provide a source of rust for the new season’s wheat crop. ▪ If these conditions are followed by a mild winter and a warm wet spring, then the chances of a leaf rust epidemic are high. Therefore, the chances of a rust epidemic are greatest following a wet summer.
- 12. ▪ Due tothe absence of the alternate host, leaf rust reproduces asexually. This reduces the variability of the rusts in the field and therefore increases the likelihood that resistant varieties will be effective for a long period of time. ▪ Rust spores are wind-blown and can be spread over large areas in a short time. The establishment of leaf rust epidemics within a crop is favoured by wet conditions and temperatures of approximately 15-22°C
- 13. ❑Control or Managementof leaf rust Resistant Varieties The best way to control leaf rust is to grow resistant varieties. Widespread cultivation of resistant varieties minimizes the levels of rust in the environment and reduces the occurrence of new races. Cultural Practices Heavy grazing or the use of herbicides during autumn to remove self-sown susceptible wheat will reduce the amount of rust in following crops. Seed Treatments There are seed treatments available which will suppress early infections of leaf rust. Seed treatments are important in susceptible varieties, especially if they are sown early or following a wet summer favouring growth of volunteers. Monitoring and fungicide spray Spray (azoxystrobin + propiconazole)/(Tebuconazole + Trifloxystrobin)/azoxystrobin/(azoxystrobin + tebuconazole) 0.2% at 7 to 10 days from flag leaf emergence to early dough grain development stage or at earliest sign of rust pustules development.
- 14. Reddish-brown, darker, powdery, oblong pustules havinga characteristic torn margin that can occur on both sides of the leaves, on the stems and the glumes. Favourable conditions: ▪ Wet conditions and ▪ Temperatures of approximately 15-30°C Alternate hosts: ▪ Berberis ▪ Mahonia ▪ Mahoberberis Black rust Disease: Stem rust (Black rust) Causal organism: Puccinia graminis f.sp. tritici
- 15. ❑ Symptoms ▪ Reddish-brown,powdery, oblong pustules having a characteristic torn margin that can occur on both sides of the leaves, on the stems and the glumes. ▪ Stem rust spores are much darker in colour than leaf or stripe rust spores. ▪ As the plant matures, the pustules produce black spores known as teliospores. They occur mainly on the leaf sheaths and stem.
- 16. Fungus carries over on volunteer cereals or barberry plant Teliosporesplay an important role by either infecting volunteer wheat plants or barberry plants Disease cycle of Stem rust Secondary cycles Fungus carries over on volunteer cereals or barberry plant Wet conditions and Temperatures of approximately 15-30°C
- 17. Management of stemrust Stem rust can be managed using an integrated approach that includes managing the green bridge, avoiding susceptible cultivars and close monitoring to enable timely fungicide sprays. Removal of the Green Bridge Rust can only survive from one season to the next on living plant material (mainly self-sown cereals). Therefore, the removal of the green bridge is essential to reduce the amount of inoculum present to infect a new crop. Variety Selection Sowing resistant varieties provides the best protection against stem rust by reducing the chance of new pathotypes occurence. Monitoring and fungicide spray Spray (azoxystrobin + propiconazole)/ (Tebuconazole+ Trifloxystrobin)/azoxystrobin/ (azoxystrobin + tebuconazole) 0.2% at 7 to 10 days from flag leaf emergence to early dough grain development stage or at earliest sign of rust pustules development.
- 18. Smut Favourable conditions: ▪ Infectionof seedlings is favored by earlier sowing ▪ Drier and acidic soils ▪ Temperature (15-21°C) Disease: Covered smut of barley Causal organism: Ustilago hordei Dark grey to black ears/heads due to the masses of teliospores of
- 19. ❑ Symptoms ▪ Thepresence of the disease is first noticed at ear emergence when the ears appear dark grey due to the masses of teliospores covered by a thin membrane of tissue. ▪ The membrane splits at maturity, or during threshing, releasing the spore mass into the atmosphere. ▪ The spores are not readily wind-dispersed if the membrane ruptures before harvest as they stick together due to the presence of an oily coating. ▪ Infected plants may be slightly shorter than their healthy neighbors. ▪ Affected ears may emerge later than the surrounding crop and in some cases remain trapped within the sheath of the flag leaf. ▪ Infected ears are readily identified by their dark color and shriveled awns. ▪ Sori can occasionally be found in stripes on leaves and stem galling has also been reported.
- 20. ❑ Control orManagement of covered smut of barley ▪ Spray Mancozeb/Tebuconazole 0.2 t0 0.3% starting just before emergence of the heads continue for two or three times if the disease is severe. ▪ Treatment of barley seeds with Provax 2.5 g/kg seeds successfully controls the disease. ▪ Use of disease resistant varieties also helps to reduce losses. ▪ Sowing seeds in a moderately dry soil will reduce the disease incidence, since moist soils are favourable for infection. ▪ The rate of covered smut infection can be reduced when barley is raised in a neutral or alkaline soil than in an acid soil.
- 21. Smutted heads, in which grain andglume structures are replaced by masses of black teliospores covered by a gray membrane, emerge several days earlier than contrasting green healthy heads The fragile membrane that covers the spores breaks off soon after heading and the spores become airborne or are washed off by rain, eventually leaving only the empty rachis as evidence of the disease. Favourable conditions: ▪ Wind and moderate rain ▪ Cool temperatures (16–22 °C) Loose smut Disease name: Loose smut Pathogen name: Ustilago tritici (Pers.) Rostr.
- 22. Bare rachis after blownoff the spores by wind and water Smutted head, where all the structures except the rachis are replaced by spores
- 24. ❑Symptoms • Loose smutis a fungal disease in which full heads are replaced by smut spores (teliospores). Conspicuous loose smut symptoms are evident at early heading. • Smutted heads, in which grain and glume structures are replaced by masses of black teliospores covered by a gray membrane, emerge several days earlier than contrasting green healthy heads. • The fragile membrane that covers the spores breaks off soon after heading and the spores become airborne or are washed off by rain, eventually leaving only the empty rachis as evidence of the disease. • The loose smut symptoms can only be seen at the time of flowering though the plants are infected right after seed germination. • The heads of the infected plants emerge earlier than the healthy one. symptoms of the disease • Yield lost in the infected heads is total. Diseased heads produce no grain at all.
- 26. ❑Management or Control •Planting high-quality pathogen-free seed will eliminate the inoculum source. • Seeds should be treated with Propvax (Carboxin + Thiram) /Tebuconazole (2.5g/kg seed) to eliminate seed borne infection. • Spray (azoxystrobin + propiconazole)/ Folicur 25EC (Tebuconazole) + Trifloxystrobin)/ azoxystrobin/ (azoxystrobin + tebuconazole) 0.05 to 0.075% at 7 to 10 days from seedling to flag leaf emergence stage or at earliest sign of loose smut development. • Using resistant cultivars helps reduce final symptoms. • Placing seed production fields away from commercial fields helps avoid infection of the seed from air-born spores, which can be carried long distances by winds.
- 27. Foot rot Disease: Footrot Causal organisms: Fusarium graminearum Fusarium culmorum Pythium graminicolum P. arrhenomanes Favourable conditions: ▪ High humidity ▪ Wet weather ▪ Warm, moist and poorly drained soils
- 28. Yellowing of the seedlingsdue to root rot Common root rots with black discolouration with sub-crown internodes (arrows) ❑Symptoms: ▪ The first visible symptoms of common root rot are the appearance of stunted seedlings with chlorotic symptoms in the field as irregular patches. ▪ The symptoms of common root rot include dark brown to black lesions in roots, sub crown internodes and stem bases. ▪ The primary and secondary roots may appear brown or blackened. ▪ The diagnostic symptoms of the Fusarium foot rot is cottony pink mycelium that may appear on the stem bases. Common root rots with black discolouration (arrow)
- 29. ❑Control or management ▪Maintain balanced fertilization particularly by reducing the application of nitrogenous fertilizer. ▪ Proper weeding to eliminate the alternate hosts and weeds may predispose the plant roots to infection. ▪ Use certified or fungicides treated seeds. ▪ Rotate crops to reduce the Fusarium inoculum by avowing the planting wheat following corn or wheat. ▪ Seeds treatment with Provax (Carboxin + Thiram) or Tebuconazole or Mancozeb + copper oxychloride @ 2.5 g/Kg seeds. ▪ Soil can be drenched with 0.2-0.3% solution of Mancozeb + Carbendazim at the seedling stage.
- 30. Late blight inPotato Disease: Late blight in potato Causal organisms: Phytophthora infestans Favourable conditions: The late blight pathogen is favored by free moisture and cool to moderate temperatures.
- 31. ❑ Symptoms The firstsymptoms 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. Initial symptoms of late blight are small, light to dark green, circular to irregular- shaped water- soaked spots.
- 32. Initial symptoms of lateblight are small, light to dark green, circular to irregular-shaped water-soaked spots. Leaf lesions frequently are surrounded by a yellow chlorotic halo Late blight lesions may be present on petioles and stems of the plant, especially in new growth where moisture persists
- 33. During active late blightgrowth, especially in cool, wet weather, a white mildew-appearing area is visible at the edge of the lesions Actively growing late blight can cause a white mildew- appearing area along petioles Brown, dry lesions can develop following warm and dry weather. A pale green to yellow border often surrounds the lesions. Often produce a distinct odour.
- 34. Late blight infectionof tubers is characterized by irregularly shaped, slightly depressed areas that can vary considerably from brown to purplish of variable size on the skin Late blight causes a tan to reddish-brown rot found under the skin. The margin of the diseased tissue is not always distinct but can be, particularly in seed potatoes that have been stored at cold storage temperatures.
- 35. ❑Management or control Destroyall cull and volunteer potatoes. • Plant late blight-free seed tubers. • Do not mix seed lots because cutting can transmit late blight. • Use a seed piece fungicide treatment labelled for control of late blight. Recommended seed treatments include Revus, Reason and mancozeb. • Avoid planting problem areas that may remain wet for extended periods or may be difficult to spray (the centre of the pivot, along powerlines and tree lines). • Avoid excessive and/or night-time irrigation. • Eliminate sources of inoculum such as hairy nightshade weed species and volunteer potatoes. • Scout fields regularly, especially in low, wet areas, along tree lines, at the centre of the pivot and other areas that remain wet for longer periods where late blight first may occur. • Use foliar fungicides on a regular and continuing schedule. Once late blight is present, only foliar fungicide applications can manage late blight in the field. (A current list of fungicides can be found in the NDSU “Fungicide Guide,” PP622).
- 36. • Keep upto date on late blight forecasts. • Quickly destroy hot spots of late blight. • Kill vines completely two to three weeks before harvest. • Applying phosphorous acid to potatoes after harvest and before piling can prevent infection and the spread of late blight in storage. • Monitor home garden and market tomatoes near you for late blight. Late blight can move from these local sources to potato fields.
- 37. Red Rot Diseaseof Sugarcane Disease: Red Rot Causal organisms: fungi Colletotrichum falcatum Favourable Conditions High day temperature (30-35˚C). Low humidity (50-60%). Low soil moisture and alkaline soils.
- 38. ❑ Symptoms • The3rd and 4th leaves (from the top) of the infected plants display yellowing and drying. At a later stage, show discoloured lesion on the rind. Fungal spores develop on rind and nodes. • If the diseased stalk split open, reddened internal tissues with intermingled white spots may be seen. The internal colour becomes brown, pith cavity become larger, greyish hyphae inside pith become visible. A sour and alcoholic smell emanates from the infected tissues.
- 39. ❑Management or control Redrot is often referred as cancer of sugarcane and no effective method for its control is available yet. However, the diseases can be managed by adopting integrated red rot management practices. • Cultivation of resistant varieties like Co 89003, Co 98014, Co 0118, Co 0238, Co 0239, Co 0124, etc will contain the disease. • The disease spread through infected setts. Therefore, always select seed canes from a disease-free healthy crop. Any setts showing reddening at the cut ends or at the nodal region should be discarded. • Raise seed crop from the seed canes treated in moist hot aerated therapy unit at 54°C for 1 hour or soak the setts overnight in Thiophanate Methyl (ROKO)+Pseudomonas. • Resort to crop rotation with paddy and green manure crops. Avoid ratooning. • During rainy season, the disease spreads fast. Bunding of affected field may be done to avoid movement of pathogen through rain or floodwater. • Roguing of diseased plants showing spindle leaf infection early during May-June and disinfecting soil around the diseased clumps with 0.1% Carbendazim solution.
- 40. Citrus canker Disease: Citruscanker Causal organisms: bacterial pathogen, Xanthomonas citri (Hasse) Dows.
- 41. Symptoms: Citrus canker causeslesions on citrus leaves, stems, and fruit. Characteristic lesions are raised and brown, have water-soaked margins, and usually have a yellow halo surrounding the lesion. Older lesions appear corky.
- 42. Management or Control: •Sanitation: Destruction of all affected trees by burning. Pruning of infected parts, particularly during dry season reduces source of inoculum. • Spraying of Fungicides: Spraying of fungicides like Bordeaux mixture and lime-sulphur is often very effective to protect the fruits against infection. It should be done during the first three months of the development of fruits. • Use of Disease Resistant Varieties: There is a possibility that cultivation of disease resistant citrus varieties may produce good results.
- 43. White rust ofCrucifers Disease: White rust Causal organisms: Albugo candida
- 44. Symptoms: Signs and symptomsof infection include chlorosis on leaf surfaces, white blister-like growths on the underside of leaves and on the stems of the plant and swelling of the roots. In addition, abnormalities in the growth of the host can occur with more serious infections. Management or control: Ploughing or disking diseased plants and plant parts results in rapid decomposition of infected tissues and helps to significantly reduce future white rust infection. Crop rotation with non-cruciferous host plants is also effective. Weed control and other sanitary methods are necessary
- 45.