General Overview

Viruses are small submicroscopic particles whereas phytoplasmas are much larger and resemble bacterial cells without a cell wall or distinct nucleus. Both require a living host and cause similar disease symptoms which include: a general dwarfing of the plant, lack of proper chlorophyll production resulting in a mottled appearance on foliage, yellowing and in some cases rings on leaves or fruit as well as necrotic (dead) areas. Symptoms may mimic those caused by 2,4-D damage or other disease organisms or even environmental problems. The disease can be spread by feeding insects or mites, or mechanically through hands and tools.

Images

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Ringspot virus on toad lity leaf (Tricyrtis)
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Virus ring spot on leaves of a moth orchid (Phalaenopsis)
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The yellow mottling on the inner, newer leaves of this summer squash (Cucurbita pepo 'White Bush Scallop') was caused by a virus; while the white patches on the outer, older leaves indicate powdery mildew
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A virus is suspected of stunting these bush beans (Phaseolus vulgaris) because of some of the leaves of the affected plants are crinkled and mottled.
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Ringspot virus on coleus (Solenostemon)
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Virus on bean (Phaseolus); note, mottling
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Virus on rose (Rosa)
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Possible virus on ruellia (Ruellia); note, bleached patterns on leaves
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Possible ringspot virus on toad lily (Tricyrtis formosana 'Gilt Edge')
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Yellow flecks on hackberry leaves (Celtis) caused by hackberry island chlorosis, a benign virus
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Note the lack of chlorophyl and deformity in the leaves of this seed-grown avocado (Persea americana), possibly caused by a virus
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Mosaic virus on rose (Rosa)
 
 
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Virus on birch (Betula)
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Suspected tobacco ringspot virus (TRSV) on astilbe (Astilbe); note circular bleached pattern on foliage
   
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Tobacco rattle virus (TRV) on peony (Paeonia). A. Phibbs, DATCP, Bugwood.org
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Virescense of hydrangea