Plant Hormones and Diseases

Plant Hormones and Diseases

1. Auxins

Auxin was discovered by Darwin in the year 1880. This is the hormone which controls the growth of plants. Its formation takes place in the apical parts of the plants.

Main functions are –

• It prevents the separation of the leaves.

• It destroys the straws.

• It saves the crops from falling.

2. Gibberellins

It was discovered by a Japanese scientist, Kurosawa, in the year 1926.
The growth hormone gibberellin was first extracted from fungus in 1938 by Yabuta and Sumiki.

Main functions are –

• It turns the dwarf plants into long plants. It helps in creating flowering.

• It helps in breaking the dormancy of the plant.

• It motivates the seeds to sprout.

• It increases the activity of cambium in the wooden plants.

• Large-sized fruits and flowers can be produced by its scattering.

3. Cytokinins

It was discovered by Miller in the year 1955, but it was named by Lethem.

Main functions are –

• It naturally works in coordination with auxins.

• It helps in cell division and development in the presence of auxins.

• It helps in breaking the dormancy of seed.

• It is helpful in making RNA and protein.

4. Abscisic Acid (ABA)

This hormone was initially discovered by Carnes and Adicote and later on by Waring.

Main functions are –

• This hormone is against growth.

• It keeps the seeds & bud in a dormant condition.

• It plays the main role in the separation of leaves.

• It delays the flowering of long-day plants.

5. Ethylene

This is the only hormone found in gaseous form. In 1962 Burg proved it as a hormone.

Main functions are –

• It helps in the ripening of the fruits.

• It increases the number of female flowers.

• It motivates the separation of leaves, flowers and fruits.

• Gas used for artificial ripening of fruit is ethane or ethylene.

6. Florigens

• It is formed in leaves but helps in the blooming of the flowers. Therefore, it is also called the flowering hormone.

7. Traumatin

• This is a type of dicarboxylic acid. It is formed in injured cells by which the injury of the plant is healed.

Other Important Botanical Concepts

• The concept of tissue culture was introduced by Haberlandt.

• The plant growth regulators are small, simple molecules of diverse chemical composition. They are indole compounds, adenine derivatives, carotenoids, and terpenes.

• Growth of plants without soil is known as hydroponics.

• For the growth of a plant, sodium is not an essential component.

• Growth of a plant is measured by the device crescograph, invented by Jagadish Chandra Bose.

Plant Diseases

1. Viral Diseases

a. Mosaic Disease of Tobacco:

• Leaves get shrunk and small.

• The chlorophyll of leaves gets destroyed.

• The factor is Tobacco Mosaic Virus (TMV), known as Bacteriophage.

• Control – Affected plants should be burnt.

b. Bunchy Top of Banana:

• Caused by banana virus.

• Plants become dwarf, and all the leaves get accumulated like a rose on the branch.

c. Yellow Vein Mosaic of Bhendi:

• Caused by a virus affecting okra plants.

• Transmitted by insects and whiteflies.

2. Bacterial Diseases

a. Wilt of Potato:

• Also known as ring disease because a brown ring is formed on the xylem.

• Caused by Pseudomonas solonacearum bacteria.

• Affects the conduction system of the plant.

b. Black Arm of Cotton:

• Caused by Xanthomonas bacteria.

• Water-soaked brown spots form on leaves.

c. Bacterial Blight of Rice:

• Caused by Xanthomonas oryzae.

• Yellow-greenish spots appear on both sides of leaves; vascular bundles get blocked.

d. Citrus Canker:

• Caused by Xanthomonas citri bacteria.

• Originated in China. Affects leaves, branches, and fruits.

e. Tundu Disease of Wheat:

• Caused by the Corynebacterium tritici and Anguina tritici nematode.

• Lower parts of leaves fade and turn yellow.

3. Fungal Diseases

• Rust of Wheat – caused by Puccinia.

• Damping Off of Seedling – caused by Pythium debaryanum.

• Red Root of Sugarcane – caused by Colletotrichum falcatum.

• Sahu Disease of Wheat – caused by insects.

Diseases Caused Due to Deficiency of Elements

Some Important Facts in Botany