The below mentioned article provides a practical experiment on the test of plant viruses.
Requirements:
1. TMV infected tobacco plant.
2. Healthy tobacco plant of the same age as that of the infected plant.
3. Homogenizer.
4. Filtration apparatus.
5. K2HPO4 – 1 % or (0.057M).
6. Distilled water, Carborundrum powder, etc.
7. Pipette, brush and spatula.
8. Glass-door chambers.
Procedure:
TMV infected tobacco leaves are collected from an infected plant and then about 10 gms of infected leaves are homogenized. The homogenization is made by glass homogenizer apparatus. The filtrate is collected and 25 ml. of 1% K2HPO4 is then added. The sap is then diluted with distilled water to give a dilution of 1/10,000.
Now a healthy potted tobacco plant is taken and the upper surfaces of the leaves are dusted with carborundum powder except one or two leaves.
Then with the help of a poster brush, spatula or by finger rubbing method, the diluted inoculum is rubbed on all the leaves, whether dusted by powder or not. Immediately after inoculation, the leaves are washed by water spray and finally the plant is kept in a shaded place devoid of insects.
Observation:
Local lesions will appear on the leaves, particularly those which were dusted with powder.
Inference:
Plant virus can be extracted in sap and then can be mechanically transmitted. Rubbing the inoculum on the dusted leaves causes light injury, which helps penetration of the virus.