Agrobacerium rhizogenes in apple causes hairy root disease.

This is correct.

Seed rot-seedling blight is caused by Bacillus subtilis while anthracnose leaf blight is caused by Colletotrichum graminicola in maize.

In coffee, warty berry disease is caused by Botrytis cinerea.

Yellow rust disease of Triticum is caused by Cochliobolus sativus. Wheat’s false eyespot disease is caused by Hymenula cerealis.

Xanthomonas campestris causes fucous blight disease in beans.

This option is correct. Both the black pit and blast diseases in citrus are caused by the bacteria Pseudomonas syringae.

Both Schizothyrium pomi and Zygophiala jamaicensis causes fly speck disease in citrus.

Scalybutt (citrus exocortis) is a disease of citrus plants, caused by the citrus exocortis viroid (CEVd). It can cause stunted growth and reduced yields in affected plants.

In apple, Diplocarpon mali and Marsonia coronaria cause ‘Marsonia blotch’ disease.

Aerolate leaf spot in citrus is caused by Rhizoctonia solani.

In apple, cotton root rot disease is caused by Phymatotrichum omnivorum, coral spot is caused by Tubercularia vulgaris, silver leaf disease is caused by Chondrostereum purpureum and quince rust disease is caused by Gymnosporangium clavipes. Hence, the sequence of codes A - 2, B - 5, C - 3, D - 1 is correct.

Kernel blight disease is caused by bacteria Pseudomonas syringae pv. syringae and basal glume rot is caused by bacteria Pseudomonas syringae pv. atrofaciens. Anthracnose, dwarf bunt and leaf rust are caused by fungal pathogens Collectotrichum cereale, Tilletia controversa and Puccinia hordei, respectively.

Grain rot is a bacterial disease caused by Burkholderia glumae and symptoms of this disease appear on seedlings and spikelets. Seedlings raised in boxes turn brown and rot. The glumes (lemma) of infected spikelets are discoloured. Initially dirty gray, they turn yellow-brown, then become dark brown and shrunken, ultimately dry. In mild infections, only the palea discolour. Brown bands can be seen distinctly over the belly of the infected kernel.

The fungus Lasiodiplodia theobromae causes black kernel rot disease in maize, leaf scald disease is caused by Rhynchosporium oryzae in rice, crown sheath rot disease is caused by Gaeumannomyces graminis and eyespot disease is caused by Drechslera gigantea. Hence, the correct answer using the codes is P - 2, Q - 4, R - 1, S - 3.