Lettuce big-vein disease causes leaf distortion and ruffling in affected lettuce

Lettuce

Lettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important...

 plants.

This disease was first associated in 1983 with a rod-shaped virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 Lettuce big-vein associated virus, which is transmitted by the obligately parasitic soil-inhabiting fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

, Olpidium brassicae

Olpidium brassicae

Olpidium brassicae is a plant pathogen. In 1983, the Alsike, Alberta area's clover was struck by a fungus epidemic of Olpidium brassicae, previously not seen in Canada.- External links :* *...

. However, in 2000 a second virus Mirafiori lettuce virus was found in lettuce showing big-vein symptoms. Furthermore, since the lettuce infected with this virus alone developed big-vein symptoms, it is considered to be a main agent of the big-vein disease.