What is Tobacco rattle
Tobacco rattle virus (TRV), previously referred to as Peony ringspot virus or Peony mosaic virus, is one of the most widespread viruses of peonies. There have been reports of this virus throughout Asia, Europe, New Zealand, and North America. TRV can infect both herbaceous (Paeonia lactiflora) and tree (Paeonia suffruticosa) peonies.
Although first described in tobacco, TRV has a wide host range of over 400 species, including: aster (Aster spp.), barley
(Hordeum vulgare), beans (Phaseolus vulgaris), beets (Beta vulgaris), brassicas (Brassicaceae), cocklebur (Xanthium spp.), common chickweed (Stellaria media), corn (Zea mays), cucumber (Cucumis sativus), faba beans (Vicia faba), gladiolus (Gladiolus spp.), iris (Iris spp.), lambsquarters (Chenopodium album), daffodil (Narcissus spp.), oat (Avena sativa), onion
(Allium cepa), peas (Pisum sativum), petunia (Petunia x atkinsiana), pepper (Capsicum spp.), pigweed (Amaranthus spp.), potato (Solanum tuberosum), purslane (Portulaca oleracea), rye (Secale cereale), shepherd’s purse (Capsella bursa-pastoris), spinach (Spinacia oleracea), sunflower
(Helianthus annuus), tulip (Tulipa spp.), and wheat (Triticum spp.). Many of these hosts are symptomless. TRV infection of potato can cause stunting, foliar symptoms (mottling, yellow ringspots or line patterns), stem mottling, as well as tuber deformation and symptoms known as corky ringspot, or spraing (necrotic flecks, arcs, or rings). As such, TRV in potato is of economic importance as corky ringspot may lower the value of a potato shipment, or make it unmarketable. The virus often remains localized to the roots of infected hosts, but in the case of peony and potato may express in the leaves. Some of these hosts can play an important role in the epidemiology of the pathogen on peony.
Tobacco rattle virus particles are rod-shaped and are composed of two single-stranded RNAs. Lengths of both particles are variable, depending on the isolate. RNA-1 is 185 to 196nm long, and RNA-2 is approximately 50 to 115nm long. The diameter of both particles is approximately 23nm. Given that a nanometer (nm) is one-billionth of a meter, these particles are extremely small and can only be seen with an electron microscope. The number of nucleotides is related to particle length, and as such, is variable. RNA-1 is approximately 7000 nucleotides long, and RNA-2 varies from 2000–4500 nucleotides. There are different methods for
What are the symptoms of TRV in peony?
TRV in peonies is most commonly expressed as ringspots of alternating green and yellow concentric circles (Figure 1) or a yellow-green mottle or mosaic. Symptoms can also appear as yellow line patterns (Figure 2) or chevrons and symptomatic tissues can turn purple or red in certain conditions (Figure 3, Figure 4). These symptoms can affect marketability of a whole plant or stems if present during flower harvest. There are no known symptoms of TRV expressed in the flower and it is unclear how the virus affects plant productivity; however, observations suggest there is no marked reduction in the vigor of infected plants.
Symptom expression of TRV in peonies, like many viruses, is highly dependent on environmental conditions. Symptoms will often appear during cooler parts of the growing season and are largely absent during the warmer months. Symptoms may also only be apparent in part of the plant while the remainder of the plant appears healthy (Figure 5; Figure 6). Even if symptoms are not visible, if any parts of the plant show or have ever shown symptoms of TRV, it is likely that the entire plant is infected with the virus. It is not possible to remove only infected plant parts or cure a peony of TRV (see “What do I do about my TRV-infected plants?”). Peonies are also susceptible to other viruses, such as Tomato spotted wilt virus (TSWV), the symptoms of which can resemble TRV. TSWV can also cause economic damage to peony and many other host species, but requires different management strategies than TRV.