diagnosis of plant disease chapter 3. objective identify common plant diseases cause by...
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Diagnosis of Plant DiseaseDiagnosis of Plant Disease
Chapter 3Chapter 3
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Objective
Identify common plant diseases cause by microorganismObserving the symptoms and sign developedCapable to relate Koch’s Postulate principles
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Symptoms and Signs
Symptoms : The visible response of a plant to a causal agent over time.
Dead spot in leaves or bark
Unnatural colour or shapeSwelling on root or branches
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Dead Spot on Leaves Swelling on Branches
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Signs : The pathogen or its parts that seen on a host plant
Observable structure of agent that cause the disease
Fungal spores
Insects on plant
Symptoms and Signs
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Fungal Spores Aphids on Plant
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Categories of Symptoms
Symptom changes of colour
Symptom death of cell
Hypertrophy & Hyperplasia
Hypotrophy & Hypoplasia
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Example of Plant Disease
SymptomsSymptom Changes of Colour
Chlorosis
Etiolation
Mosaic
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Chlorosis
Yellowing of leaves due to:
Loss of chlorophyll pigment/lack of active chlorophyll
Nutrient deficiencies
Toxicity of material (pesticide)
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Etiolation
Symptom of yellowing & elongation of stems/leaves
Due to the lack of light (under dark condition)
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Mosaic
Formation of light and dark green/yellow mosaic pattern on leaves
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Symptom Death of Cell Necrosis
General necrosis Local necrosis
Soft rot
Dry rot
Vascular wilt
Leaf spots
Anthracnose
Downy mildew
BlightPowdery mildew
Canker
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General Necrosis
Local Necrosis
Occur in the whole plant that causes rot
of plant / tissue
The necrosis sites are limited
Only involved a part or few plant cells /
tissues
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General Necrosis –
Soft RotOccur to the fruit &vegetable that cause by the bacteria (Erwinia carotovora)
The infected part become rot and watery
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General Necrosis -
BlightThe fast and overall death of plant tissue such as shoot or leaves
Pathogens kill the cells / tissues with which they are in close contact and become generally distributed.
Example - Potato late blight (Phytophthora infestans)-fungus
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Local Necrosis – Leaf Spots
Spot of death cell or the presence of small necrotic areas on leaves
Might caused by virus, fungal, bacteria, insect bites, etc.
Example :
Bacteria leaf spot – Xanthomonas campestris pv. vesicatoria
Septoria leaf spots - fungus
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Bacteria Leaf Spot on Pepper Septoria Leaf Spot
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Local Necrosis - Anthracnose
Normally infected by imperfect fungi or Ascomycetes
Produces blackish lesions on fruits, stem & leaf
Blackness being due to the presence of dark spores, mycelium or both
Example –
Mango : Colletotrichum gloeosporioides
Cucurbit : Colletotrichum lagenarium
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Necrosis – Cankers
Sunken areas in wood
Death of plant parts
Most are caused by fungi (Ascomycetes), but - a few bacterial cankers
Example – Durian cankers = Phytophthora palmivora (fungus)
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Necrosis-Powdery Mildew
The appearance of powdery spots on the leaves
Example - Powdery mildew on cucurbit =Erysiphe cichoracearum (fungus)
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Local Necrosis – Downey Mildew
The occurrence of yellowish rectangular spot on the leaves
Example – Downey mildew on cucurbit - Pseudoperonospora cubensis, (fungus)
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Symptom of Hyperplastic Deformation
Hypertrophy Hyperplasia
Gall
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Hyperplastic Deformation : Abnormal outgrowths of the plant host
Hypertrophy : Overgrowth of plant organ or plant size because the increasing of cell sizes
Hyperplasia : Overgrowth of plant organ or plant size because the increasing of cell numbers or cell multiply rapidly.
Both gave the same results to the plant where the size of plant tissue or plant organs increased than usual (abnormal size)
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Gall
Localized swellings of plant organ
May caused by various pathogens such as bacteria, fungi, nematodes and insects.
Examples –
Crown gall = Agrobacterium tumefaciens (bacteria)
Root knot = Meloidogyne spp (nematodes)
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Bacteria Crown Gall- affect root & stem
Root Knot – attack root
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Witches' Broom
Appear as a cluster of small shoots
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Curls
The leaves become twisted and curled
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Symptom of Hypoplasia
Retardation
DwarfingOne or more members
of a plant are significantly smaller than standard members
of their species
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Hypoplasia
The underdevelopment of plant tissue and organs due to the smaller production than normal cells
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Hypotrophy : the under-development of plant organ or plant size because the reducing of cell sizes
Hypoplasia : the under-development of plant organ or plant size because the reducing of cell numbers
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Principle of Koch’s
Postulates4 criteria designed to verify that the microorganism is the causal agent for the disease.
4 rules / steps:
The suspected pathogen must be consistently associated with the diseased plant
The microorganism must be isolated from the diseased organism and grown in pure culture.
The cultured microorganism should cause disease when inoculated into a healthy organism.
The microorganism must be reisolated from the inoculated plant and grown in a pure culture. The microorganism should have the same characteristic with the original culture.