Common diseases of Cassava and diseases assessment in west Africa
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Transcript of Common diseases of Cassava and diseases assessment in west Africa
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
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Summary of Presentation
Introduction
Constraints
Plant diseases and it importance
Disease symptoms
Disease Assessment/Rating
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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
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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.
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Is an impairment of the normal state of plant
that is interrupts or modifies Its vital functions
Plant Diseases
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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
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Abiotic disease
• Don’t spread from plant to plant
• Causes
-adverse environment
- chemical injuries
-Adverse soil condition
-Soil structure
-Soil fertility
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Biotic/infectious disease
Disease triangle
Pathogens Host
Environment
-Fungi-Bacteria-Nematode-viruses
SpeciesCultivarAge
Temp, RH, wetness
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Symptoms and sign
Symptoms:Expression of a disease by plant
SignVisible presence of a pathogen
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Virus symptoms
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Bacterial symptoms
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Symptom on Stem
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Symptom on root
Wet Rot Complex
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Sclerotium tuber rot
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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).
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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
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CASSAVA PESTS AND DISEASES
EVALUATION
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Cassava mosaic disease (CMD)
Brief description
First reported in East Africa in 1894 it is the most common cassav a disease in Africa.The etiology of cassava mosaic was confirmed beyond doubt in 1983; though it was postulated in 1906 that the causal organism was a virus.
The causal organism, CMV, is a geminivirus (paired or bonded virus particles) averaging 20X30 nanometers.VECTOR: Whitefly (Bemisia tabaci)
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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)
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22
CASSAVA BACTARIAL BLIGHT (CBB )
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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).
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Cassava Anthracnose Disease (CAD)
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EVALUATING FOR CAD1
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
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26
CASSAVA GREEN SPIDER MITE
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EVALUATING FOR CGM1
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
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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
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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
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Thank you