Friday, March 29, 2013

Fancy plants may be carriers of virus


Moses-in-a-boat (Rhoeo discolor) exhibits dimorphic coloration: healthy plants are green and robust, while the infected ones are pink and stunted pink (center). Such suspicious characteristic should be referred to specialists to prevent further spread.  Humans are the most common agents of transmission of viral and other diseases. 
 Tomato infected with mosaic virus may display unusual colors of fruits and leaves thought to be associated with soil nutrient deficiency and varietal characteristics.  The virus is cosmopolitan, and infects not only the members of the Family Solanaceae such as eggplant, tobacco, pepper, Irish potato, but a host of other plants belonging to other families. More than a hundred field crops are susceptible to the virus. 
Yellowish and stunted, the plant continues to grow, reproduce and complete its life cycle while carrying a virus that cause the bunchy top appearance of the plant - rosette arrangement of the leaves.  Local folks unaware of the condition of the plant just regard it as fancy, which then favors its spread in the banana plantation   
Red pepper (Capsicum annuum), healthy (left) and infected with mosaic virus (early stage) may appear the same, but plant pathologists can easily detect the difference. The virus does not kill the plant, it exaggerates the mosaic and chlorotic patterns as fancy characteristics.  This exacerbates the spread of the disease starting with touch to insect bite to plant-to-plant contact in the field. 

 
  "Frog eye" spots and chlorotic venation, including stunting and early defoliation are attributed to a complex of pathogens, with the virus as among the primary causes.  Host is Terminalia catappa   



Facts about plant viral diseases.

1. Viruses in general cannot be seen with the naked eye. Not even the laboratory light microscope. With the electron microscope we can see and study them.

2. The largest group are mosaic viruses.  They cause yellow and green spotting of leaves, stems blossoms and fruits.

3. Mosaic destroys chlorophyll, resulting to stunted growth, and therefore poor harvest, and may lead to the death of the plants usually in the later stage. 

4. Another group of viruses is called yellows, that causes yellowing, leaf curling and dwarfing.Mode of attack is to block the plant's vascular system, preventing water and nutrients to pass through. Infected plants show no symptoms, and therefore transmit the disease without detection. 

5. Plant viruses enter the cells directly through wounds caused by weather, humans, and vectors like aphids, whiteflies, and leafhoppers, mealy bugs, and other organisms which pierce the plant and such its sap. Horticultural practices like grafting and inarching direct transfer the virus.  

6. Viral infected plants cannot be cured.  It is through prevention that can stop the disease from being introduced or from spreading.

7. Foremost is quarantine.  Second is to plant only virus free seeds, because viral disease is systemic, that is, all parts of the plant carries the virus.

8. Rouging infected plants and burning them is a common method on the farm. Eliminate volunteer crops as these may serve a continuing or alternate host of the virus.

9. Crop rotation and fallowing (allowing the farm to rest) breaks the life cycle of the disease.

10. Tobacco mosaic caused by a virus, Marmor tabaci, is cosmopolitan.  It is known to infect more than 150 types of plants which include vegetables, flowering plants and weeds. 

11. The most important plants infected belong to Family Solanaceae which is composed of commercial crops valued at billions of dollars in world agriculture and trade - tomato, tobacco, eggplant, pepper, Irish potato.

12. Virus-infected plants are mistaken for overdose in pesticide spray, side effect of herbicides, pollution in various forms, but the most confusing likeness is deficiency in  minerals like iron, zinc, and boron, although these are needed by plants in trace quantities.  Ferrous deficiency causing chlorosis and stunting, often thought to be incipient viral signs.

13. Viruses differ from fungi and bacteria in that they do not produce spores or other structures capable of penetrating plant parts. Viruses enter through wounds, and spread through farming practices.

14. Tobacco virus survives manufacturing process - drying, redrying and making cigars and cigarettes.  It remains dormant up to 20 years .  Then it resurrects on a healthy tobacco plant or any member of the solanaceous family – by the mere touch of a smoker – and the virus in no time spreads like fire infecting field after field.
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15. On entering a host the virus begins to multiply by inducing host cells to produce more of its kind. Viruses do not cause disease by consuming or killing cells but by taking over the metabolic cell processes, resulting in abnormal cell functioning. 

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