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Viruses that Enhance the Aesthetics of Some Ornamental Plants: Beauty or Beast?

Microbes including fungi, bacteria, and viruses commonly cause diseases in humans, animals, and plants. Nevertheless, there are many beneficial microbes. Recently, researchers proved that a phytoplasma is the biological agent causing free-branching in poinsettias which is an economically beneficial trait for their producers. Beneficial viruses for plants have been discovered as well. Symptoms due to virus infections include foliar mosaic, mottle, ring spots, necrosis, malformation, curling/rolling, yellow vein, flower and/or foliage variegation, fruit malformations, and overall plant stunting. However, interactions between plant viruses and their hosts do not always result in disease. There are other viruses that can cause desirable effects in their hosts, and infected plants have been selected or in some cases used by ornamental horticulturists to enhance their aesthetics. Plants with unusual foliage and/or flowers are highly sought by horticulturists and many ornamental plant enthusiasts. Selections of many ornamental plants exhibiting green leaves with other colors such as white, yellow, or red, alone or combined (generally known as variegations) have been propagated and commercialized as distinct cultivars. Similarly, this practice has been conducted with flowers exhibiting desirable aesthetic value, usually in the form of flower breaking (flowers in which petals are variegated due to the irregular distribution of pigment). Plant viruses can cause symptoms that mimic genetic variegations and vein discolorations. In this paper, we discuss some viruses that enhance natural beauty of certain ornamentals and increase their commercial value, and we discuss potential drawbacks and repercussions associated with their use.