(a) Discuss briefly the rosette disease of groundnut under the following headings: (i) causal organism: (ii) symptoms (iii) method of transmission; (iv) dam...

Answer Details

(a) Rosette disease:

(i) Causal organism: Rosette disease is caused by a virus called Groundnut Rosette Virus (GRV). It is transmitted from plant to plant by an insect vector known as the groundnut aphid (Aphis craccivora).

(ii) Symptoms: Infected plants show symptoms such as excessive branching, development of small leaves, and the formation of rosettes (bunches of small leaves at the top of the plant). The pods are also small and poorly developed.

(iii) Method of transmission: The groundnut aphid is the vector that transmits the virus from plant to plant. It feeds on infected plants and carries the virus to healthy plants.

(iv) Damage done: The virus causes significant yield losses in groundnut production. Infected plants have reduced growth, low yields, and poor-quality pods.

(v) Preventive and control measures: The following measures can be taken to prevent and control the spread of Rosette disease: planting of disease-resistant varieties, crop rotation, intercropping with non-host crops, destruction of infected plants, and use of insecticides to control the groundnut aphid vector.

(b) Calculation of plant population:

To calculate the plant population expected in a portion of land measuring 60 m x 30 m with a spacing of 30 cm x 30 cm, we need to convert the dimensions of the land into centimeters. 60 m x 30 m = 6000 cm x 3000 cm.

Next, we calculate the area of the land in square centimeters: 6000 cm x 3000 cm = 18,000,000 square centimeters.

To calculate the number of plants per square meter, we need to divide the area of each plant (30 cm x 30 cm = 900 square centimeters) by the area of one square meter (100 cm x 100 cm = 10,000 square centimeters).

So, the number of plants per square meter is: 10,000 square centimeters / 900 square centimeters = 11.11 plants per square meter.

Finally, to calculate the plant population expected in the portion of land, we multiply the number of plants per square meter by the total area of the land: 11.11 plants per square meter x 18,000 square meters = 199,980 plants.

Therefore, we can expect a plant population of approximately 199,980 in a portion of land measuring 60 m x 30 m with a spacing of 30 cm x 30 cm.