Potato spindle tuber viroid
Encyclopedia
The Potato spindle tuber viroid ("PSTVd") was the first viroid
to be identified. PSTVd is a small, circular RNA
molecule closely related to the Chrysanthemum stunt viroid. Present within the viroidal RNA is the Pospiviroid RY motif stem loop
. The natural hosts are potatoes (Solanum tuberosum) and tomatoes (Lycopersicon esculentum). All potatoes and tomatoes are susceptible to PSTVd and there is no form of natural resistance. Natural infections have also been seen in avocado
s and infections in other solanaceous crops have been induced in the laboratory.
Long distance spread of PSTVd usually occurs via infected seeds but transmission via aphid
s (Myzus persicae) also occurs but only in the presence of PLRV (potato leaf roll virus). Mechanical transmission also occurs once it has been introduced to an area.
s.
The nucleotides which are highlighted are found in most other viroids.
, Canada
, Russia
and South Africa
. It causes quite severe losses and in some regions, it is one of the most destructive diseases of potatoes (solanum tuberosum). The Potato spindle tuber viroid (PSTVd) was the first viroid to be identified. Natural infections have also been seen in avocados and other solanaceous crops. It attacks all varieties, spreads rapidly, and often occurs in combination with virus diseases. It also attacks tomato but seems to be of little economic importance in that crop. So far PSTVd has not been detected in New Zealand
potato crops, but it is possible that infection may occur if growers do not take care. With this in mind this broadsheet describes how they spread and can be controlled and damage and symptoms they cause in potatoes.
As reported by George N. Agrios infected potato plants appear erect, spindly, and dwarfed. The leaves are small and erect and the leaflets are darker green and sometimes show rolling and twisting in figure 1. Once potato plants are mature, symptoms can be more obvious on tubers as shown in (figure 2). Affected tubers can be small, narrow or spindle-like and may develop knobs and swellings. In some varieties, eyes are numerous, shallow and more prominent and tubers are often cracked as shown in (figure 3). Yield losses of up to 64% have been recorded in potato crops infected by PSTVd.
The pathogen Potato Spindle Tuber Viroid(PSTV) is the first recognized viroid. PSTV is infectious RNA of low molecular weight, approximately 100,000 Daltons
. The RNA is single stranded molecule of 359 nucleotides with extensive regions of base pairing. Under the electron microscope, purified but denatured PSTV appears as short strands about 50 nm long and thickness of double stranded DNA.
PSTV is mechanically transmissible and is spread primarily by knives used to cut healthy and infected potato “seed” tubers and during handling and planting of the crop. PSTV seems to also be transmitted by pollen and seed and by several insects including some aphids, grasshoppers, flea beetles and true bugs. The transmission by insects is apparently nonspecific and incidental, that is on contaminated mouth parts and feet of insects visiting the plants.
Apply hygiene procedures if there has been an outbreak of PSTVd. Wash equipment (knives, cutters, sprayers, cultivators) with sanitizers before moving to another field or sowing another seed-line. Viroids are resistant to heat sterilization so sometimes freezing or chemical treatments are more effective. So equipment, surfaces and tools can be disinfected with sodium or calcium hypochlorite
(bleach) and 2% sodium hydroxide. Chemicals such as Virkon
and quaternary compounds such as Dermasan can be used.
Viroid
Viroids are plant pathogens that consist of a short stretch of highly complementary, circular, single-stranded RNA without the protein coat that is typical for viruses. The smallest discovered is a 220 nucleobase scRNA associated with the rice yellow mottle sobemovirus...
to be identified. PSTVd is a small, circular RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
molecule closely related to the Chrysanthemum stunt viroid. Present within the viroidal RNA is the Pospiviroid RY motif stem loop
Pospiviroid RY motif stem loop
The Pospiviroid RY motif stem loop is an RNA element found in Pospiviroids such as potato spindle tuber viroid . The RY nucleotide sequence motif in PSTVd, is thought to bind with the tomato protein Virp1. The exact function of this motif and the significance of Virp1 binding is unknown...
. The natural hosts are potatoes (Solanum tuberosum) and tomatoes (Lycopersicon esculentum). All potatoes and tomatoes are susceptible to PSTVd and there is no form of natural resistance. Natural infections have also been seen in avocado
Avocado
The avocado is a tree native to Central Mexico, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel...
s and infections in other solanaceous crops have been induced in the laboratory.
Strains
Different strains of PSTVd exist and symptoms range from mild to severe. Mild strains produce no obvious symptoms. Symptoms in severe strains are dependent on environmental conditions and are most severe in hot conditions. Symptoms may be mild in initial infections but become progressively worse in the following generations. Common symptoms of severe infections include colour changes in the foliage, smaller leaves and spindle like elongation. Sprouting also occurs at a slower rate than in unaffected potatoes. Infected tomatoes are slower to show symptoms which include stunted growth with a ‘bunchy top’ caused by shortened internodes. Leaves become yellow or purple and often become curled and twisted. Necrosis eventually occurs in the veins of the bottom and middle leaves and the top leaves don’t die but are reduced in size. Fruit ripening is also affected leading to hard, small, dark green tomatoes.Long distance spread of PSTVd usually occurs via infected seeds but transmission via aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s (Myzus persicae) also occurs but only in the presence of PLRV (potato leaf roll virus). Mechanical transmission also occurs once it has been introduced to an area.
Primary and secondary structure of the PSTVd viroid
The PSTVd viroid has 359 nucleotideNucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s.
| Primary Structure |
1 CGGAACUAAA CUCGUGGUUC CUGUGGUUCA CACCUGACCU CCUGAGCAGA AAAGAAAAAA 61 GAAGGCGGCU CGGAGGAGCG CUUCAGGGAU CCCCGGGGAA ACCUGGAGCG AACUGGCAAA 121 AAAGGACGGU GGGGAGUGCC CAGCGGCCGA CAGGAGUAAU UCCCGCCGAA ACAGGGUUUU 181 CACCCUUCCU UUCUUCGGGU GUCCUUCCUC GCGCCCGCAG GACCACCCCU CGCCCCCUUU 241 GCGCUGUCGC UUCGGCUACU ACCCGGUGGA AACAACUGAA GCUCCCGAGA ACCGCUUUUU 301 CUCUAUCUUA CUUGCUUCGG GGCGAGGGUG UUUAGCCCUU GGAACCGCAG UUGGUUCCU |
| Secondary Structure |
 |
The nucleotides which are highlighted are found in most other viroids.
Identity name: Potato Spindle Tuber
The potato spindle tuber disease occurs in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. It causes quite severe losses and in some regions, it is one of the most destructive diseases of potatoes (solanum tuberosum). The Potato spindle tuber viroid (PSTVd) was the first viroid to be identified. Natural infections have also been seen in avocados and other solanaceous crops. It attacks all varieties, spreads rapidly, and often occurs in combination with virus diseases. It also attacks tomato but seems to be of little economic importance in that crop. So far PSTVd has not been detected in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
potato crops, but it is possible that infection may occur if growers do not take care. With this in mind this broadsheet describes how they spread and can be controlled and damage and symptoms they cause in potatoes.
Figure 1: Foliar infection of potato spindle tuber viroid
Showing stiff upright growth habitFigure 2: Tuber infection of potato spindle tuber viroid
Showing spindle shaped tubers (right)Figure 3: Tuber infection of potato spindle tuber viroid
Showing cracked tubersAs reported by George N. Agrios infected potato plants appear erect, spindly, and dwarfed. The leaves are small and erect and the leaflets are darker green and sometimes show rolling and twisting in figure 1. Once potato plants are mature, symptoms can be more obvious on tubers as shown in (figure 2). Affected tubers can be small, narrow or spindle-like and may develop knobs and swellings. In some varieties, eyes are numerous, shallow and more prominent and tubers are often cracked as shown in (figure 3). Yield losses of up to 64% have been recorded in potato crops infected by PSTVd.
The pathogen Potato Spindle Tuber Viroid(PSTV) is the first recognized viroid. PSTV is infectious RNA of low molecular weight, approximately 100,000 Daltons
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
. The RNA is single stranded molecule of 359 nucleotides with extensive regions of base pairing. Under the electron microscope, purified but denatured PSTV appears as short strands about 50 nm long and thickness of double stranded DNA.
PSTV is mechanically transmissible and is spread primarily by knives used to cut healthy and infected potato “seed” tubers and during handling and planting of the crop. PSTV seems to also be transmitted by pollen and seed and by several insects including some aphids, grasshoppers, flea beetles and true bugs. The transmission by insects is apparently nonspecific and incidental, that is on contaminated mouth parts and feet of insects visiting the plants.
Method to control disease
Potato spindle tuber can be controlled effectively by planting PSTV-free potato tubers in fields free of diseased tubers that may have survived from the previous year’s crop. Plant whole seed tubers rather than cut pieces. Avoid contact with leaves (either by staff or equipment) during field operations. Control insects, especially aphids and chewing species. Carefully remove the infected plants from the healthier plants, bag them and burn plants that are suspected of being infected well away from production areas. Monitor the crop carefully.Apply hygiene procedures if there has been an outbreak of PSTVd. Wash equipment (knives, cutters, sprayers, cultivators) with sanitizers before moving to another field or sowing another seed-line. Viroids are resistant to heat sterilization so sometimes freezing or chemical treatments are more effective. So equipment, surfaces and tools can be disinfected with sodium or calcium hypochlorite
Calcium hypochlorite
Calcium hypochlorite is a chemical compound with formula 2. It is widely used for water treatment and as a bleaching agent...
(bleach) and 2% sodium hydroxide. Chemicals such as Virkon
Virkon
Virkon is a multi-purpose disinfectant. It contains oxone , sodium dodecylbenzenesulfonate, sulphamic acid; and inorganic buffers. It is typically used for cleaning up hazardous spills, disinfecting surfaces and soaking equipment...
and quaternary compounds such as Dermasan can be used.