Correct option is D
Explanation:
Apple scab (A) is caused by the fungus Venturia inaequalis (IV), which produces scab lesions on apple leaves and fruits.
Ergot of cereals (B) is caused by the fungus Claviceps purpurea (I), which infects grains and produces toxic alkaloids.
Fire blight (C) is caused by the bacterium Erwinia amylovora (II), leading to wilting and necrosis of shoots and blossoms in apple and pear trees.
Root-Knot (D) is caused by the nematode Meloidogyne spp. (III), which induces galls (knots) on roots, impairing nutrient uptake.
Information Booster:
Apple scab is a major fungal disease managed by fungicides and resistant varieties.
Ergot disease causes contamination with toxic ergot alkaloids, posing food safety risks.
Fire blight is a serious bacterial disease requiring pruning and chemical control.
Root-knot nematodes are soil-borne pests affecting root systems of many crops worldwide.
