(a) State each of the disease condition observed on specimens J (MAIZE PLANT) and K (CASSAVA LEAF) and their causative agents. (b) Explain the mode of trans...

(a) Disease condition and causative agent

• Specimen J (maize plant): the leaves show a mottled mosaic pattern, the disease is maize mosaic disease, and its causative agent is a virus.
• Specimen K (cassava leaf): the leaf shows brown circular spots, the disease is cassava leaf spot, and its causative agent is a fungus.

(b) Mode of transmission

• Specimen J: the virus is transmitted from plant to plant by an insect vector, the aphid.
• Specimen K: the fungus is airborne and is also spread by water and rain splash.

(c) Two effects and two control measures of each disease

Specimen J (maize mosaic) effects: it reduces the photosynthetic area of the leaf and causes stunted growth with a reduction in yield. Control: use resistant varieties and practise early planting; also eradicate the insect vectors and remove and burn infected plants.

Specimen K (cassava leaf spot) effects: it reduces the photosynthetic area of the leaf and lowers the rate of growth and yield of the crop. Control: apply fungicides and use resistant varieties; also remove and burn infected plants and practise crop rotation.

(d) Two other diseases of specimen K (cassava)

• Cassava mosaic disease.
• Cassava bacterial blight.