Virus diseases of Prunus species—Tomato ringspot virus
Tomato ringspot virus causes damage that varies with the virus strain. The virus has numerous hosts including almond, nectarine, peach, Mahaleb and Mazzard cherry, and Myrobalan plum. Note that Prunus species can be affected by numerous other viruses and their importance varies in part depending on the particular host, such as with cherry viruses.
Identification
Depending on the combination of scion wood and virus strain, either prunus stem pitting or yellow bud mosaic may develop. Because the pathogen is spread from tree to tree by soil-dwelling, root-feeding nematodes, where groups of susceptible hosts grow together the symptoms tend to appear on trees in one area then spread outward.
Prunus stem pitting. This disease affects cherry, nectarine, peach, and plum. Infected trees leaf out later than normal. Foliage appears pale green or yellowish and wilted in early summer. In late summer, foliage may prematurely develop reddish or purple fall coloration. Fruit size and yield are greatly reduced. Affected fruit may drop before it is mature.
Foliage and fruit symptoms are caused by a reaction at the graft union that interferes with the flow of water and nutrients. This results in poor water availability in the scion. This causes foliage symptoms similar to those caused by Armillaria root rot, Phytophthora root and crown rot, and crown- and root-chewing rodents such as pocket gophers. A distinguishing characteristic of this viral disease is abnormally thick and spongy bark at the base of the tree just above and below the soil line. The wood underneath is deeply grooved and pitted. The wood may be weakened to the point that the tree falls over.
Yellow bud mosaic. This disease primarily affects almond, cherry, nectarine, and peach. Apricot and plum can be infected, but they are not significantly damaged. Viral infection causes foliage to become distorted and pale green to yellowish. Newly flushing leaves may remain undersized and become bright yellow, resulting in the yellow bud symptom. Foliage symptoms slowly spread throughout the canopy as the virus moves up into scion wood.
On cherry trees, a bare-limb appearance starts at the bottom of branches and moves upward as the virus kills small branches, spurs, and twigs. Affected leaves develop prominent, whitish veins at right angles to the midrib. Leaflike growths (enations) may develop along the midrib on the underside of these leaves.
Life cycle
Tomato ringspot virus is spread by budding and grafting with infected wood and by soil-dwelling, root-feeding dagger nematodes, Xiphinema species. The virus is seedborne in dandelion, Taraxacum officinale. Other weed hosts include bristly oxtongue, chickweed, lambsquarters, little mallow, mullein, plantain, spurge, and white clover.
The nematode vector acquires the virus by feeding on the roots of infected hosts. Xiphinema larvae remain infective until they molt. Adults remain infective for 3 to 8 months after acquiring the virus. Disease spread from tree to tree may follow the movement of water in soil because the nematodes move with water. Cultivation of nematode-infested soil and irrigation help to spread the nematode vectors.
Solutions
Tomato ringspot virus management requires a combination of methods. Use pathogen-free planting stock obtained from a reputable commercial supplier. Plant virus-resistant rootstocks such as Colt. Use good sanitation to avoid spreading nematode-infested soil. Prevent water runoff from areas of diseased trees to where healthy trees are growing. Control weeds because some species are hosts of the virus and its pathogen-vectoring nematodes.
Promptly remove diseased trees, especially those growing near healthy hosts. After cutting down infected trees consider promptly treating the stumps with a systemic herbicide registered (labeled) to kill stumps, which includes certain glyphosate formulations such as Roundup Weed and Grass Killer Super Concentrate. This prevents the roots from continuing to support the nematode vectors.
Adapted from Integrated Pest Management for Stone Fruits and Pest Management Guidelines: Cherry, University of California Statewide Integrated Pest Management Program (UC IPM). |
Stone fruit leaves distorted and yellowed by the yellow bud mosaic strain of Tomato ringspot virus.
Yellow, undersized peach leaves (top left), the symptom for which the yellow bud mosaic strain of Tomato ringspot virus is named.
Stone fruit foliage that is reddish in August (photo right) due to infection by the prunus stem pitting strain of Tomato ringspot virus.
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