1. PPA 601: PLANT DISEASES & THEIR MANAGEMENT LECTURE 1
Mr.Esava.Tabua

2. LESSON OBJECTIVE
Judge economic importance, symptoms and causal agents, disease cycle and management of diseases of Rice, Sorghum, Pearl Millet, Maize and Wheat.

3. WHAT ARE CEREALS?
Cereal is an actual grass, usually cultivated for the edible starch components of its grain.
Botanically, this grain is a type of fruit known as a caryopsis, which contains three parts such as the endosperm, germ, and bran.
Cereals belongs to the monocot family Poaceae and is grown in larger quantities and provides more food energy and carbohydrate for the entire world than any other type of crop.
Considered as staple crops in some countries around the world.
Rich source of macronutrients (carbohydrates, fats, oils, and protein) and micronutrients (vitamins, minerals) as well as bioactive phytochemicals (polyphenols, flavonoids, anthocyanin, carotenoids, etc.).

4. Example of Cereal (Wheat) (Source: Jayalath, 2014)

5. What is a Plant Disease? A plant disease refers to abnormal growth or dysfunction of a plant. or Diseases are the result of some disturbance in the normal life process of the plant. Diseases may be the result of living and/or non-living causes. Biotic diseases are caused by living organisms (e.g., fungi, bacteria, and viruses).

6. ECONOMIC IMPORTANCE OF DISEASES
Disease infestations can cause epidemics which brings loss to every farmer as most striking damage will produce.
Disease usually influence the economic development of certain countries, and have led frequently to acute distress and famine.

7. Rice Diseases (Sheath Blight)
Sheath blight is a fungal disease caused by Rhizoctonia solani.
Symptoms: Usually observed from tillering to milk stage in a rice crop. It occurs throughout the rice- growing areas in temperate, subtropical, and tropical countries. Rice sheath blight is found in all rice production areas, and is decreasing rice production especially in intensified production systems. Studies at IRRI showed that sheath blight causes a yield loss of 6% across lowland rice fields in tropical Asia. (IRRI)
Rice Diseases (Sheath Blight)

8. The initial infection occurs on the stem near the water line and appears as a water soaked oval lesion which often dries and turns tan.
The fungus moves over resistance mechanisms (Dark bands around the lesion)and from plant to plant by surface or aerial hyphae.
Lesions vary in appearance due to wetness, age, host resistance. and fungicide use. Lesions tend to be darker on resistant plants and after fungicide use.
Leaf lesions usually develop the characteristic snake skin like pattern.
All plant parts are susceptible to infection except the roots

9. R. solani can infect rice from the seedling stage to harvest maturity.
In some place however the disease usually develops after tillering.
The pathogen overwinters as small seed like structures called sclerotia or as mycelium in infected plant debris. This material floats in the first flood and comes in contact with the rice plants. It tends to accumulates toward one side of the field due to wind.

10. Sheath blight tends to develop in circular areas in the field and cause what are called bird nests. The earlier this happens the more damage is done to the rice crop.
Sclerotia are formed on the plant surface and start as white bean like structures that turn dark brown to black. They fall into the flood water and sink. Cells develop air pockets and can then float or they are incorporated into the soil and can survive up to 20 years.
Sheath blight development is favored by thick stands and high nitrogen rates which increase canopy thickness resulting in higher moisture levels. Rice following rice or soybeans is more likely to be affected.
Resistance to sheath blight is available but resistance tends to be associated with taller and later maturing plant types. Rice breeders are actively trying to find and incorporate resistance into current varieties.

11. Disease Cycle

12. Management Practices
Plant varieties less susceptible to sheath blight.
Plant as early as possible within the recommended planting period.
Avoid late planting.
Avoid excessive plant stands.
Do not over fertilize with nitrogen.
Apply a fungicide if necessary.

13. RICE BLAST DISEASE # 2

14. CAUSAL AGENT Imperfect stage(anamorph): Pyricularia oryzae
Imperfect stage(anamorph):
Pyricularia oryzae
Perfect Stage: Magnaporthe grisea

15. P. oryzae can infect rice from the seedling stage to harvest.
develops during tillering (leaf blast) and at heading (panicle blast) maturity.
The pathogen overwinters as spores in infected plant debris. The fungus produces new spores in the spring that reinfects rice.

16. Spores are carried by wind and splashing rain
Spores are carried by wind and splashing rain. Movement can be over long distances.
The fungus infects the plant by the spore germinating and forming an aspersorium (a thick fungal cell) on the plant surface and then exerting a hostoria (feeding structure) into the plant cells. A minimum of 8 hours is needed for infection to occur.

17. Most plant parts are susceptible to infection except the roots.
The initial infections occurs on leaves usually around tillering and appear as diamond, football, or spindle shape lesion with pointed ends. Lesions start as small water soaked areas on young leaves and enlarge into diamond shape with a blue gray cast which are the fungal spores. Lesions often dry out and turn tan with a brown border. Lesion shape and size can vary.

18. Head infections usually develop at the joint just below the head (neck blast)or on individual panicle branches (panicle blast).The head can break off at neck lesion can cause what is called rotten neck blast.

19. After stem elongation nodes can be infected causing node blast
After stem elongation nodes can be infected causing node blast. Symptoms usually appear as white heads and unexplained lodging.

20. The fungus produces many spores ,on stalk like structures called sporangia, in the presence of a favorable environment and a susceptible host and causes numerous new infections in the field and neighboring fields. They are carried by wind and water over long distances.
Blast development is favored by thick stands and high nitrogen rates which increase canopy thickness resulting in higher moisture levels but is most severe under upland or drained conditions. Other conditions that favor blast are sandy soils and fields lined with trees.

21. Resistance to blast is available but resistance tends to break down over time as the fungus adapts to new resistant varieties. Resistance to leaf blast is not always correlated to panicle resistance.

22. Blast Reactions
Susceptible Moderately Susceptible Moderately Resistant Resistant
Cheniere Jupiter
Cocodrie CL CL Catahoula CL161 Trenasse Neptune Cypress
Wells Pirogue
CL151
Bengal

23. Losses due to blast include severe reductions in yield, milling, and the cost of applying fungicides. Unlike most rice diseases blast is very explosive and can completely destroy a crop in a very short time.

24. Scouting or Determining Need
Varieties with low levels of resistance should be scouted for leaf blast during the vegetative stages of growth. There are no predictive systems for rotten neck blast. Since significant damage is already done when rotten-neck or panicle blast are first detected, preventive sprays are required on susceptible varieties when blast has been detected in the area.
A number of other rice diseases can be confused with blast.

25. Fungicides are available to control blast
Fungicides are available to control blast. Unless plants are dying, leaf blast is not treated with a fungicide. Fungicide applications are typically applied at boot (2-4 inch panicle in the flag leaf sheath) and 50 70% heading. If only one application can be made the heading growth stage is the most effective timing. Fungicides must be applied no later than 50 70% heads emerging to be effective.

26. MANAGEMENT PRACTICES Plant varieties resistant to blast.
Avoid late planting.
Plant as early as possible within the recommended planting period.
For leaf blast, reflood if field has been drained. Maintain flood at 4 -6 inches to ensure soil is covered.
Do not over fertilize with nitrogen.
Apply a fungicide if necessary.

27. Bacterial Leaf Streak Disease:
Pathogen: This is a bacterial disease, caused by a bacterium Xanthomonas oryzae pv. oryzicola.

28. Symptoms
Initially, small, dark-green and water-soaked streaks are seen on interveins from tillering to booting stage.
These streaks are dark-green at first and later enlarge to become yellowish gray and translucent.
Numerous small yellow beads of bacterial exudates appear on surface of lesions under humid conditions.
Brown to greyish white lesions may develop and sometimes yellow halo develop around the lesions.
The affected leaves become bleached and greyish white and brown and finally these leaves dry up.

29. Management
The disease can be controlled by proper application of fertilizers, proper planting spacing, and hot water treatment of seeds.
Field sanitation is important. Ratoons, straws and volunteer seedlings left after harvest can be destroyed to minimize the initial inoculum at the beginning of the season. Providing good drainage system especially in seedbeds can also manage this disease.
Seed treatment with streptocycline (1g) + carbendazim 50 W.P. (20g) for 8– 10 kg of seed in 10 litres of water for 12 – 15 hours.
Spray the crop 3–4 times with the mixture of copper oxychloride (500 g) and streptocycline (7.5g) in 500 litres of water for one ha at 12–15 days intervals.  

30. Bacterial Leaf streak Disease

31. Stem Rot Disease
Pathogen: This disease is caused by a fungus Sclerotium oryzae.

32. Symptoms
Initial symptoms of the disease are small, irregular black lesions on the outer leaf sheath near water level.
These lesions expand as the disease advances and severely infected stems rot.
Numerous tiny white and black sclerotia and mycelium inside the infected culms are visible.
Infected culm collapses and plant lodges.
If the diseased tiller is opened, profuse mycelial growth and large number of sclerotia can be seen.
The sclerotia may be seen in the stubbles after crop harvest. The disease causes unfilled panicles and chalky grain. Severe infection causes death of tillers. The disease aggravates lodging of plants.

33. Stem rot disease

34. Management
Burning straw and stubble or any crop residue after harvest or allowing the straw to decompose and draining the field can reduce sclerotia in the field.
Balanced use of fertilizers or split application with high potash and lime to increase soil pH reduces stem rot infection.
Deep ploughing in summer is helpful to reduce the inoculum level for next crop season.
Avoid standing water in the field for a long period and improve drainage facility in the fields where disease occurs in endemic form. Avoid flow of irrigation water from infected fields to healthy fields.
5. Spray fungicides like mancozeb or 1.5–2.5g/litre. Chemicals such as fentin hydroxide sprayed at the mid-tillering stage, thiophanate-methyl sprayed at the time of disease initiation can reduce stem rot incidence in the rice field. The use of validamycin–A is also effective against the fungus.

35. The end!!
Any Questions