ISHS Acta Horticulturae 88: III Conference on Epidemiology and Control of Virus Diseases of Vegetables
THE ECOLOGY OF YELLOWING VIRUSES |
| Author: | J.E. Duffus |
| Abstract:
After a brief historical survey of major diseases caused by yellowing viruses, i.e. the agents of disorders characterized by stunting of infected plants, accompanied by rolling, yellowing, reddening and brittleness of affected leaves, some aspects of their ecology are reviewed. Virus inducing yellowing diseases have special affinities to the phloem. They fall into three distinct groups: viruses transmitted by whiteflies; semipersistent aphid-transmitted viruses with flexuous, filamentous particles and persistent aphid-transmitted viruses. Disease agents transmitted by whiteflies can be placed into three separate groups. One of the groups induces color deviations of the variegation type on affected leaves. Another group induces leaf curl type symptoms, with crinkling, vein etching and leaf enations. The third group, transmitted by Trialeurodes sp. instead of Bemisia sp., induces typical yellowing type symptoms with rolling and brittleness of affected leaves. The semipersistent aphid-transmitted viruses with long, flexuous, filamentous particles are a small but economically significant group. There is no evidence of serological relationships between members of the group tristeza virus and beet yellow stunt virus. They closely resemble each other in vector relationships, particle morphology, symptomatology, including yellowing and necrosis, and in difficulty of sap inoculation. The persistent aphid transmitted viruses have been categorized into four groups: The luteovirus group, pea enation mosaic group, sowthistle yellow vein group; and carrot motley dwarf group. Pea enation mosaic, which induces mosaic and enation symptoms and is readily mechanically transmitted, should probably remain in a separate group. Sowthistle yellow vein, lettuce necrotic yellows and Brassica necrotic yellow with distinctive bacilliform particles, which are propagative in their insect vectors, should also be a separate group. Carrot mottle virus is probably incorrectly categorized as a persistent aphid transmitted virus since it is not transmitted by aphids except in presence of the persistent aphid-transmitted virus carrot red leaf. The most important and widespread viruses are those of the luteo virus group: beet western yellows, barley yellow dwarf and some members of the potato leafroll complex. Some isolates of potato leafroll virus may differ in two important ways. Virus replication in the aphid vector has been reported and some isolates appear to contain DNA not RNA; a | |
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