Ergot of rye is caused by a species ofa. Clavicepsb. Phytophthorac. Uncinulad. Ustilago

The correct answer is a. Claviceps.

Explanation: Ergot of rye is a fungal disease caused by the species Claviceps purpurea. This fungus infects the flowers of rye and other cereal crops, producing toxic compounds known as ergot alkaloids. These alkaloids can cause a condition known as ergotism when consumed by humans or animals. Ergotism can lead to symptoms like convulsions, hallucinations, and gangrene.

Here’s a brief description of the other options:

b. Phytophthora is a genus of water molds that causes diseases like late blight in potatoes.
c. Uncinula is a genus of fungi that causes powdery mildew diseases on various plants.
d. Ustilago is a genus of smut fungi that affects cereals and grasses, but it does not cause ergot.
Thus, Claviceps is the correct genus responsible for ergot of rye.