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Common diseases of Cassava and diseases assessment in west Africa

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Cassava diseases
Plant Diseases

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Common diseases of Cassava and diseases assessment in west Africa

  1. 1. www.iita.orgA member of CGIAR consortium COMMON DISEASES OF CASSAVA AND DISEASES ASSESSMENT IN WEST AFRICA Presented by Oguntade Oluwole Laboratory Manager, Germplasm Health Unit IITA, NIGERIA
  2. 2. www.iita.orgA member of CGIAR consortium Summary of Presentation  Introduction  Constraints Plant diseases and it importance  Disease symptoms  Disease Assessment/Rating
  3. 3. www.iita.orgA member of CGIAR consortium Cassava Production Cassava, Manihot esculenta Crantz (Euphorbiaceae) is a starchy root crop that is among the most important tropical food crops. It has the ability to produce economic yields under marginal production conditions, this crop helps to alleviate problems of hunger and carbohydrate intake deficiency, and thus its importance in terms of food security in African continent cannot be over-emphasized. Cassava constitutes the principal carbohydrate source for more than 800 million people in developing countries. About 80% of the cassava produced is consumed by humans, while the remaining 20% is used for animal feeds and agro-industrial purposes. Introduction
  4. 4. www.iita.orgA member of CGIAR consortium Constraints  Despite the importance of this crop the production is constraint by Insect pests and plant diseases which reduce cassava yields substantially, posing a threat to food security throughout the developing world.  While agricultural scientists have recognized these threats, assessments of cassava pests and diseases can only be done if the various symptoms caused by the different disease can be identified.
  5. 5. www.iita.orgA member of CGIAR consortium Is an impairment of the normal state of plant that is interrupts or modifies Its vital functions Plant Diseases
  6. 6. www.iita.orgA member of CGIAR consortium Two types of plant disease • Abiotic diseases/disorder are cause by noninfectious agents such as weather, stress, nutrient deficiency, chemical injury, soil factors e.t.c • Biotic diseases/disorder are caused by infectious agent such as virus, fungi, bacteria and nematodes
  7. 7. www.iita.orgA member of CGIAR consortium Abiotic disease • Don’t spread from plant to plant • Causes -adverse environment - chemical injuries -Adverse soil condition -Soil structure -Soil fertility
  8. 8. www.iita.orgA member of CGIAR consortium Biotic/infectious disease Disease triangle Pathogens Host Environment -Fungi -Bacteria -Nematode -viruses Species Cultivar Age Temp, RH, wetness
  9. 9. www.iita.orgA member of CGIAR consortium Symptoms and sign Symptoms: Expression of a disease by plant Sign Visible presence of a pathogen
  10. 10. www.iita.orgA member of CGIAR consortium
  11. 11. www.iita.orgA member of CGIAR consortium
  12. 12. www.iita.orgA member of CGIAR consortium Virus symptoms
  13. 13. www.iita.orgA member of CGIAR consortium Bacterial symptoms
  14. 14. www.iita.orgA member of CGIAR consortium Symptom on Stem
  15. 15. www.iita.orgA member of CGIAR consortium 15 Symptom on root Wet Rot Complex
  16. 16. www.iita.orgA member of CGIAR consortium Sclerotium tuber rot
  17. 17. www.iita.orgA member of CGIAR consortium Disease incidence (%) = Number of symptomatic plants X 100 Total number of plants Disease severity = Is the overall of degree damage caused by a disease symptom to a plant part e.g. leaf stem or root. For example anthracnose disease severity rating of 1-5 where; 1 = Symptomless leaves, 2 = 1-25% leaf spot/blight/mosaic 3 = 26-50% leaf spots /blight/mosaic 4 = 51-75 leaf spots/blight/mosaic 5 = Plant with severe leaf symptoms and chlorotic, covering more than 75% of the leaf area. *Generic scale Disease rating and assessment of cassava disease symptoms DISEASE ASSESSMENT: is the amount of disease that is present. This can be measured as the proportion of a plant community that is diseased (disease incidence) or as the proportion of plant area that is affected (disease severity).
  18. 18. www.iita.orgA member of CGIAR consortium To know the prevalence and extent of damage caused by a disease Importance of disease assessment and measurement  To develop effective management strategies  Help in taken good decision during certification
  19. 19. www.iita.orgA member of CGIAR consortium CASSAVA PESTS AND DISEASES EVALUATION
  20. 20. www.iita.orgA member of CGIAR consortium Cassava mosaic disease (CMD) Brief description First reportedinEast Africa in 1894 it is the most commoncassava disease inAfrica. The etiology of cassava mosaic was confirmed beyonddoubt in 1983; though it was postulated in1906 that the causal organism was a virus. The causal organism, CMV, is a geminivirus (paired or bondedvirus particles) averaging 20X30 nanometers. VECTOR: Whitefly (Bemisia tabaci)
  21. 21. www.iita.orgA member of CGIAR consortium 21 1. = No visible symptoms (highly resistant) 2: 3: 4: 5: =mild chlorotic patterns on entire leaflets or mild distortion at base of leaflets, rest of leaflets appearing green and healthy (moderately resistant). = strong mosaic patterns on entire leaf, and narrowing and distortion of lower one-third of leaflets (tolerant) = severe mosaic, distortion of two-thirds of leaflets and general reduction of leaf size (susceptible). = severe mosaic, distortion of four-fifths or more of leaflets, twisted and misshapen leaves (highly susceptible)
  22. 22. www.iita.orgA member of CGIAR consortium 22 CASSAVA BACTARIAL BLIGHT (CBB )
  23. 23. www.iita.orgA member of CGIAR consortium 23 EVALUATING FOR CASSAVA BACTERIAL BLIGHT (CBB) 1 2 3 4 5 = No visible symptom (Highly resistant) = lesion around one point of inoculation on the leaves (Moderately resistant) = extension and appearance of new lesions on the stem and beginning of first leaves to wilt (Tolerant) = extensive leaf wilt and defoliation and stem die- back(Susceptible). = extensive leaf wilt , defoliation, stunting and die back forming candle stick (Highly susceptible).
  24. 24. www.iita.orgA member of CGIAR consortium 24 Cassava Anthracnose Disease (CAD)
  25. 25. www.iita.orgA member of CGIAR consortium 25 EVALUATING FOR CAD 1 2 = many deep cankers on stems followed by distortion (Tolerant) 4 = many oval lesions on stems (Susceptible) 5 = No visible symptoms (Highly Resistant) = few shallow cankers on woody stems, late in the growing season (Moderately Resistance). = many lesions on stems and severe necrosis at leaf axils, followed by wilting and severe defoliation (Highly Susceptible) 3
  26. 26. www.iita.orgA member of CGIAR consortium 26 CASSAVA GREEN SPIDER MITE
  27. 27. www.iita.orgA member of CGIAR consortium 27 EVALUATING FOR CGM 1 2 3 4 5 = apparently no visible symptoms = slight reduction in leaf size and internode length = serious reduction in leaf size and internode length = severe bunch top symptoms; obvious reduction of internode length and severe reduction in leaf size and leaf area = candlestick appearance; internode length reduced, young portion of shoot curved and completely defoliated
  28. 28. www.iita.orgA member of CGIAR consortium Field inspection scoring sheet for quality control in cassava seeds system Observation Comments Field Ref. No. GPS information Variety Type of seed (select on) • Pre-basic • Basic • Certified Date of planting Total size of the farm Isolation distance Spacing between plants Inspectors Field details Note: Maximum thresholds for pests and diseases. Fields exceeding these values for any parameter are rejected. Parameter Basic seed Certified Off type 10% 20% *CMD (mosaic) 10% 20% *CAD (Anthracnose) 10% 20% *CBB (bacterial blight) 10% 20% *CM (mealybug) 10% 20% *CGM (green mite) 10% 20% Scale insects 0% 20% *Refers to percent plants with mean severity score of ≥3
  29. 29. www.iita.orgA member of CGIAR consortium Scoring Sheet Scring sheet   Name of the evaluator:   Ref. No. Field size   Date/Time Crop stage (Age in weeks)   Location name Varieties   District   Region Intercrops   Agro-ecology   Latitude Crops in neighbouring fields   Longitude   Altitude (m) Researcher (farmer)   Summary Percent infection: Average severity: Severity range: Row number Number of plants Number of virus infected plants (Score 1) % healthy- looking plants Number of virus infected plants (>score 3) % infected plants Number of anthracnose ‘blight’ affected plants (>score 3) % infected plants
  30. 30. www.iita.orgA member of CGIAR consortium Thank you

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