VIRUSES AND VIRUS DISEASES OF ALLIUM SPECIES

Onion was among the first crops found to suffer from a damaging 'mosaic disease', but the identity of the causal 'onion yellow dwarf virus' remained uncertain until the recent detection of the related, but distinct, leek yellow stripe virus. Research on the two potyviruses revealed the existence of shallot latent virus. Garlic seems to be riddled with a number of poty- and carlaviruses but research on them, though going on in many laboratories, is still fragmentary, and their identity and relationships to the three Allium viruses above remain uncertain.

Eight other viruses, seven of them mainly known from other plant species, have also been reported from Allium species, but information on their importance is limited.

Some Allium viruses are of recognized economic importance but the role of the carlaviruses seems to be underestimated. Some of the virus diseases of Allium crops can be easily controlled through hygienic measures, but others may require breeding for resistance. Promising results have been obtained in freeing garlic from virus(es) by tissue culture. Application of this technique to free shallot from shallot latent virus deserves further attention.

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