Spindle Tuber Of Potato Crops: Treating Potatoes With Spindle Tuber Viroid

Spindle Tuber Of Potato Crops: Treating Potatoes With Spindle Tuber Viroid

By: Amy Grant

Potatoes with spindle tuber viroid were first reported as a disease of potatoes in North America, but the disease was first spotted on tomatoes in South Africa. In tomatoes, the disease is referred to as tomato bunchy top virus, while the common name with regards to spuds is spindle tuber of potato or potato spindle tuber. Today, spindle tuber viroid has been detected in potatoes throughout most of the world, with strains running from mild to severe.

Symptoms of Potatoes with Spindle Tuber Viroid

Spindle tuber of potato disease is a pathogen whose main host is potatoes but which may also affect tomatoes and solanaceous ornamentals. No obvious symptoms are observed in potatoes with mild strains of the disease, but severe strains are another story.

With severe infections, potato foliage will be spindly with overlapping leaflets, sometimes upward rolling, often twisted and wrinkled. Leaves at ground level are often in an upright position rather than those in healthy plants which rest on the ground.

Overall, plants will be stunted. Tubers may have any one of the following abnormalities:

  • elongation, cylindrical, spindle, or dumb-bell shape
  • prominent eyes
  • surface cracking
  • small size

Some cultivars with potato spindle tuber develop swellings or knobs and are severely deformed. With each generation, the foliage and tuber symptoms become more pronounced.

Symptoms of spindle tuber viroid in potatoes may be confused with those of nutrient imbalances, insect or spray damage, or other diseases. Symptoms of the disease are more obvious during warm weather combined with full sun exposure.

How to Control Spindle Tuber Viroid in Potatoes

In order to learn how to manage this disease, it helps to know how it is transmitted – usually by contact between healthy and diseased plants via mechanical equipment like tractors or garden tools, and animal or human interaction with the plant.

The initial infection of the viroid into the potatoes is through infected seed tubers. The secondary infection occurs through contact mentioned above. Transmission can also occur through pollen but only to pollinated seeds, not to the parent plant. Aphids may also transmit the viroid, but only when potato leafroll virus is present as well.

To control spindle tuber of potato, use only certified tuber seed. Practice good crop sanitation. Wear sanitary gloves of vinyl or latex when handling infected plants and then dispose of them before moving on to healthy plants. Remember, plants may be infected but not showing symptoms. They are still disease carriers, so practicing sanitary garden habits should be consistent.

Garden tools should be sanitized in a 2% solution of sodium hypochlorite or a similar disinfectant. Clothing can pass the infection from plant to plant, so be sure to change your clothing and shoes if you have been working amongst diseased plants.

There are no biological or chemical controls for spindle tuber of potatoes. Potatoes that are infected with the disease and plants nearby that may be infected should be removed and either burned or buried deeply.

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What Is Potato Spindle Tuber - Learn About Spindle Tuber Viroid In Potatoes - garden

VIROIDS are the smallest replicating pathogenic agents known 1 . Composed entirely of RNA, they have genome sizes in the range of 330-380 nucleotides 2 , 10 times smaller than the smallest bacteriophage of Escherichia coli 3 . Although there is no evidence for the existence of a protective protein coat for viroids, they infect a wide variety of plants and in many produce severe disease symptoms 1,4 . The molecular mechanisms by which viroids replicate and interact with their hosts are not yet understood. In its most severe form, the disease 5,6 caused by potato spindle tuber viroid (PSTV) causes general stunting of potato plant growth, deformity of the upper foliage, and production of disfigured potatoes 5 . Mild strains of PSTV which produce barely detectable symptoms have also been isolated 7 . Furthermore, plants infected by mild strains are somehow protected from developing symptoms following subsequent inoculation with severe strains 8,9 . This biological protection phenomenon has been called cross-protection 7 . As the only known component of viroids is RNA, mild and severe strains must differ in nucleotide sequence. The study described here aimed to determine the extent of this difference.

An outbreak of Potato spindle tuber viroid in tomato is linked to imported seed

In 2011, an outbreak of the quarantine-regulated pathogen Potato spindle tuber viroid (PSTVd) occurred in a commercial glasshouse-grown tomato crop in Queensland, Australia. Phylogenetic studies showed that the genotype of this isolate grouped in a cluster of PSTVd genotypes from tomato and Physalis peruviana, and exhibited an interesting mutation (U257→A) that has previously been linked to lethal symptom expression in tomato. Transmission studies showed that the viroid could be mechanically transmitted from crushed fruit sap, but not from undamaged fruits. A low rate of asymptomatic infection was determined for plants in the affected glasshouse, demonstrating the efficacy of using symptoms to detect PSTVd infections in tomato. No PSTVd infections were detected in solanaceous weeds located outside of the infected glasshouse, excluding them from playing a role in the viroid epidemiology. Monitoring and subsequent testing of new tomato crops grown in the facility demonstrated successful eradication of the pathogen. A trace-back analysis linked the outbreak of PSTVd to an infected imported tomato seed-lot, indicating that PSTVd is transmitted internationally through contaminated seed.

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Due to the lack of capsid proteins, we cannot use serological techniques (E.L.I.S.A., in particular) suitable for detecting the virus S. The detection method makes use of molecular techniques or electrophoresis.

PSTVd is a quarantine organism in most areas, e.g. the European Union, and is therefore subject to mandatory control measures.

The control of PSTVd basically consists of planting certified seed potatoes which are derived from seed tubers that have been tested and are free of PSTVd. Most certification schemes include strict controls on the introduction of plant material (general trade and genetic resources). As ornamentals may be symptomless reservoirs, it is also important to take care with the introduction of ornamental solanaceae coming from infected areas (South America, Asia, Central Europe, etc.) and to avoid movement of personnel, equipment or plant materials into potato fields from susceptible host plants (ornamentals or horticultural crops such as tomato).

In case of an outbreak of PSTVd, it is important to apply stringent hygiene procedures:

  • wash and disinfect equipment, surfaces and tools before moving to another field or planting another seed lot
  • plant whole seed tubers rather than cut pieces
  • control insects, especially aphids and chewing species
  • carefully inspect, remove and destroy infected as well as suspicious plants
  • apply a strict and thorough viroid testing programme.

Viroids Disease and Examples

Some example of plant viroids are

  • Potato spindle tuber viroid (potatoes)
  • Citrus exocortis (citrus plants) (sometimes called “scalybutt”) this can also infect tomato plants (sometimes called “tomato bunchy top disease”)
  • Citrus gummy bark viroid
  • Grapevine viroid
  • Dapple peach fruit disease viroid
  • Citrus cachexia viroid
  • Cucumber pale fruit viroid
  • Dapple plum and peach fruit disease viroid
  • Cadang-cadang is a disease caused by Coconut cadang-cadang viroid (a lethal viroid of Coconut)
  • Peach latent mosaic viroid (present in all peach- and nectarine-producing areas of the world)
  • Eggplant latent viroid.

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