We need to match common plant diseases with the vegetable crops they typically affect.
(A) Purple blotch: Caused by the fungus Alternaria porri, this is a significant disease of Allium species, including onion and Garlic (I).
(B) Black rot: Caused by the bacterium Xanthomonas campestris pv. campestris, this is a major disease of cruciferous vegetables like cabbage, broccoli, and Cauliflower (II).
(C) Anthracnose: Caused by fungi of the genus Colletotrichum, anthracnose affects a wide range of crops. It is a serious disease of Chilli (III), causing fruit rot and leaf spots.
(D) Powdery mildew: Caused by various species of erysiphaceous fungi, this disease appears as a white powdery coating on leaves and other plant parts. It is a common and widespread disease affecting many crops, including Pea (IV) (Erysiphe pisi).
Therefore, all the direct matches are correct:
(A) - (I)
(B) - (II)
(C) - (III)
(D) - (IV)
This corresponds to option (1).
(A) - (I), (B) - (II), (C) - (III), (D) - (IV)