Peach latent mosaic viroid

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...

is a type species from the genus Pelamoviroid, which belongs to the family Avsunviroidae

Avsunviroidae

The Avsunviroidae are a family of viroids. At present three members are known of. They consist of RNA genomes between 246-375 nucleotides in length. They are single stranded covalent circles and have intramolecular base pairing. All members lack a central conserved region.-Replication:Replication...

. This family is characterized as having chloroplastic viroids with hammerhead ribozyme

Hammerhead ribozyme

Hammerhead RNAs are RNAs that self-cleave via a small conserved secondary structural motif termed a hammerhead because of its shape. Most hammerhead RNAs are subsets of two classes of plant pathogenic RNAs: the satellite RNAs of RNA viruses and the viroids. The self-cleavage reactions, first...

s. Peach latent mosaic viroid is a 336-351nt

Nucleotide

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...

 circular RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 which has a branched formation. This branched formation is stabilised by a pseudoknot

Pseudoknot

A pseudoknot is a nucleic acid secondary structure containing at least two stem-loop structures in which half of one stem is intercalated between the two halves of another stem. The pseudoknot was first recognized in the turnip yellow mosaic virus in 1982...

 between two kissing loops. Peach latent mosaic viroid was first described in the 1980s in Spain by a group of scientists. It is present in all peach

Peach

The peach tree is a deciduous tree growing to tall and 6 in. in diameter, belonging to the subfamily Prunoideae of the family Rosaceae. It bears an edible juicy fruit called a peach...

- and nectarine-producing areas of the world including Europe, Asia, North America and South America and the frequency of naturally occurring infection is high. Before the development of symptoms the disease is latent in peach trees for approximately 5-7 years. The symptoms of the disease include necrosis

Necrosis

Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...

 of buds, delayed shoot development, necrotic branches, premature ageing of trees, flower streaking, ripening deformations, enlarged rounded stones, circular discoloured areas on the fruit skin and in some cases mosaic, blotch, vein banding or calico appearance on infected leaves. Peach latent mosaic viroid is horizontally spread from plant to plant across a field by propagation of infected buds, pruning tools and green peach aphid

Myzus persicae

Myzus persicae, known as the green peach aphid, is a small green aphid. It is the most significant aphid pest of peach trees, causing decreased growth, shriveling of the leaves and the death of various tissues...

s. Vertical transmission of peach latent mosaic viroid through seeds can not occur.