Diagnosis of Plant Disease

1. Diagnosis of Plant Disease Chapter 3

2. Objective • Identify common plant diseases cause by microorganism • Observing the symptoms and sign developed • Capable to relate Koch’s Postulate principles

3. 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 shape • Swelling on root or branches

4. Dead Spot on Leaves Swelling on Branches

5. Symptoms and Signs 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

6. Fungal Spores Aphids on Plant

7. Categories of Symptoms • Symptom changes of colour • Symptom death of cell • Hypertrophy & Hyperplasia • Hypotrophy & Hypoplasia

8. Symptom Changes of Colour Chlorosis Etiolation Mosaic Example of Plant Disease Symptoms

9. Chlorosis Yellowing of leaves due to: • Loss of chlorophyll pigment/lack of active chlorophyll • Nutrient deficiencies • Toxicity of material (pesticide)

10. Etiolation • Symptom of yellowing & elongation of stems/leaves • Due to the lack of light (under dark condition)

11. Mosaic • Formation of light and dark green/yellow mosaic pattern on leaves

12. Symptom Death of Cell Necrosis General necrosis Local necrosis Leaf spots Soft rot Anthracnose Dry rot Downy mildew Vascular wilt Powdery mildew Blight Canker

13. 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

14. General Necrosis – Soft Rot • Occur to the fruit &vegetable that cause by the bacteria (Erwiniacarotovora) • The infected part become rot and watery

15. General Necrosis - Blight • The 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

16. 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

17. Bacteria Leaf Spot on Pepper Septoria Leaf Spot

18. 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

19. 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)

20. Necrosis-Powdery Mildew • The appearance of powdery spots on the leaves • Example - Powdery mildew on cucurbit =Erysiphe cichoracearum (fungus)

21. Local Necrosis – Downey Mildew • The occurrence of yellowish rectangular spot on the leaves • Example – Downey mildew on cucurbit - Pseudoperonospora cubensis, (fungus)

22. Symptom of Hyperplastic Deformation • Hypertrophy • Hyperplasia Gall

23. 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 ofcell numbersor 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)

24. 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)

25. Bacteria Crown Gall- affect root & stem Root Knot – attack root

26. Witches' Broom • Appear as a cluster of small shoots

27. Curls • The leaves become twisted and curled

28. Symptom of Hypoplasia Retardation Dwarfing One or more members of a plant are significantly smaller than standard members of their species

29. Hypoplasia • The underdevelopment of plant tissue and organsdue to the smaller production than normal cells

30. 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

31. Principle of Koch’s Postulates • 4 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.