ABSTRACT
Onion, also known as the bulb onion or common onion, is a vegetable and is the most widely cultivated species of the genus Allium. Onion is cultivated and used around the world. The onion plant is characterized by a fan of hollow, bluish-green leaves, and its bulb at the base of the plant begins to swell when a certain day length is reached. A variety of diseases and disorders affect onion crop. During the early stages of bulbing, onions are highly susceptible to leaf blight. White spots surrounded by a greenish halo disease is more prevalent in the densely populated crops of onion in the United Kingdom but more destructive in the temperate regions of the world. Onion neck rot caused by a necrotrophic fungus named Botrytis aclada is a post-harvest disease. The pathogen enters the onion bulb through the succulent necks when the tops are removed or through wounds and matured leaves.
