Practical 8: Plant Virology

OBJECTIVES

1.      To learn how to conduct mechanical inoculation on plant.

2.      To learn what is the symptoms of the plant that affected by virus.

INTRODUCTION

Viruses are sub-microscopic , infectious particles that are multiplied only inside living host cells. The basic shape of plant viruses are  elongate, cylindrical rod and spherical. The two main components of viruses are protein coat and nucleic acid. The infectious component of viruses is the nucleic acid. Viruses are obligate parasite which they must live in a living tissue before they can reproduce themselves. Viruses infect the plant cell through wounds. Usually they disseminate by biological agent such as nematode , insects and humans.

MATERIALS

-          Diseased leaf

-          Test host plant

-          Mortar and pestle

-          Carborundum

-          Distilled water

METHODS

A) Mechanical Inoculation.

    I.            The virus inoculum was prepared by crushing the diseased leaf using mortar and pestle until uniform extract obtained. 0.5-1 ml of distilled water are added to the extract.

II.            The leaf surface of the host plant are rubbed with Carborundum to cause injury and make opening on the leaf surface. Only a small amount of carborundum are used.

 III.            The leaves are washed using the distilled water to remove the excessive lea pieces and sap from the leaf surface.

 IV.            The virus inoculum are applied on the injured leaves by gently wiping the inoculum 3-4 times across the upper epidermis by using soft piece of cloth or forefinger to the leaves.

Diseases leaf, mortar and pestle, distilled water, test host plant and carborundum.	The diseased leaf are crushed with mortar and pestle.
Carborundum are rubbed onto the leaf surface.	The leafs are washed with distilled water.
The virus inoculum are put on the leaf.	The virus inoculum on leaf.
Health plant vs Inoculated plant	After 1 week. The leaf show the symptom.

B) Disease symptoms.

    I.            The symptoms of the affected plant are observed.

RESULT

Disease	Symptoms	Causal agent
Chlorosis	·         Yellowing of the foliage. ·         Leaf tissue become yellowing.	Cucumber mosaic virus (CMV)
Necrosis	·         Death of cell tissue ·         Wilted	·         Tobacco necrosis virus ·         Cymbidium mosaic virus
Mosaic	·         Discoloration of leaves ·         Distortion of leaves ·         Stunting	·         Cucumber mosaic virus (CMV)
Ringspot	·         Ringspot on leaves or fruit ·         Stunted	·         Papaya ring spot virus (PRSV)
Veinclearing	·         Discoloration on leaves and fruits ·         Quick decline on the whole tree.	·         Citrus Tristeza