Onion yellow dwarf virus

Introduction

A virus with flexuous filamentous particles c. 775 nm long. Readily transmitted by several aphid species in the non-persistent manner and by inoculation of sap, mainly to certain Allium species. It is probably distributed world-wide. Selected synonyms are

• Allium virus 1
• Marmor cepae

Main Diseases

Causes onion yellow dwarf: stunting of first-year onion (Allium cepa) plants, with the leaves showing irregular yellow striping to almost complete yellowing, downward curling, flattening, crinkling and flaccidity also causes deterioration during storage and premature sprouting of onion bulbs. In onion seed plants, the virus causes striping, curling and distortion of flower stems, reduction in the number of flowers and seeds, and impairment of seed quality.

Geographical Distribution

Reported from most countries where onions are cultivated.

Transmission by Vectors

Several aphid species have transmitted the virus experimentally, and may do so in the field when briefly probing in passing, because none is prevalent on Allium crops. Acquisition and inoculation is in short feeding times and aphid infectivity is rapidly lost. Myzus ascalonicus may spread the virus among onion bulbs and sprouts during storage.

Particle Structure

Particles are flexuous filaments, 722 nm long and 16 nm in diameter, or over 800 nm long. They can easily be detected in extracts of diseased onion leaves chopped in phosphotungstic acid, and often occur in aggregates.