Which one of the following is a Protozoal disease

Correct option is D

Several plant diseases caused by protozoa or protozoa-like organisms affect important crops. Empty root of cassava, heart rot of coconut, and phloem necrosis of coconut are all associated with protozoal or phytoplasma-type infections. Therefore, all the listed diseases fall under the category of protozoal diseases.
Information booster: Protozoal and protozoa-like diseases often affect the vascular tissues, leading to systemic symptoms in plants. Such diseases are commonly transmitted by insect vectors, making their management more complex. Symptoms usually include wilting, internal decay, and degeneration of conductive tissues. Control measures mainly focus on vector management and removal of infected plants.
Why other options are incorrect: (a) This option is incomplete because empty root of cassava is not the only protozoal disease listed. (b) This option is incorrect because heart rot of coconut alone does not cover all protozoal diseases given. (c) This option is incorrect because phloem necrosis of coconut is only one among several protozoal diseases.