Sharka disease

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Sharka disease on an apricot

Scharka (or Scharka disease ) is a plant disease of stone fruit caused by the Scharka virus ( plum pox virus, PPV) . It particularly affects plums / plums and also peaches / nectarines and apricots and is their most important disease, which has spread in Germany since the 1960s and is now present across the board.

As a result of the disease, the commercial cultivation of plums / plums in particular is affected by a decline in yield and poor fruit quality.

Sharka virus

Sharka virus genome

The causative agent of Scharka is a thread-like, 20 x 764 nanometers wide (+) ssRNA virus from the genus of potyviruses , are known from the four strains (D, M, C, and EA). These virus strains lead to different manifestations of the symptoms and also vary in the choice of host plants. The 750 nm long pathogen can be detected using the ELISA or the PCR method.

Symptoms

Leaf symptoms
Fruit symptoms

Infection with the Sharka virus leads to various symptoms, the severity of which can vary depending on the variety. In spring (May / June), light olive-green to olive-green rings form on the leaves of plums / plums, which can develop into black dots from dead tissue. Smallpox-like or linear depressions appear on the fruit, below which the flesh (up to the stone) takes on a reddish color and a rubbery consistency. As a result of the infestation, the fruit may fall off prematurely.

The symptoms appear particularly frequently and clearly in the case of warmth and drought during the growing season .

Origin and transmission

The symptoms caused by this virus were first observed in Bulgaria in 1917, and Sharka was first described by Dimitar Atanasov in 1933 and recognized as a viral disease. Sharka can now be found in almost all of Europe.

Aphids (especially green peach aphid , large plum aphid , green plum aphid and hop aphid ), which have ingested the pathogen on an infected tree, act as vectors ( vectors ) at short distances . Over greater distances, it is spread through refinement with infected rice or documents .

Combat

Sharka-resistant (genetically modified) plum variety

The Sharka virus and the symptoms of Sharka disease caused by it cannot be combated directly.

Only the spread can be avoided / reduced by:

  • Control of the transmitting insects
  • Clearing infected plants
  • Use of virus-free documents and travelers
  • Use of low virus susceptibility / resistant varieties and rootstocks

Based on the Sharca Ordinance, the responsible authorities can order the clearing and destruction of infested plants.

Stone fruit in infested areas can only be grown with suitable varieties. Attempts are currently being made to breed Scharka-resistant or Scharka-tolerant plum / plum varieties. As the first (and so far only) completely Scharka-resistant variety, the variety " Jojo " was bred at the University of Hohenheim in 1981 . However, there are a number of varieties that are not resistant but are only slightly damaged by the Sharka virus.

Reporting requirement

According to the "Ordinance to Combat Sharka Disease", the disease is subject to mandatory notification , and control measures are also regulated.

Sharka susceptibility / tolerance / resistance

The different types of stone fruit are - depending on their individual, genetically determined resistance - differently susceptible to Sharka disease. There are

  • susceptible varieties - the tree shows severe symptoms, is badly damaged, and the fruits are not marketable. In part, a differentiation is made here according to the degree of susceptibility (also depending on environmental factors such as drought).
  • Tolerant varieties - the tree shows no symptoms, or only a few or few symptoms, may be slightly damaged, but the fruits are marketable ("fruit shark tolerance"). In part, a differentiation is made here according to the degree of susceptibility (also depending on environmental factors such as drought).
  • resistant varieties - the tree cannot be infected or an infection is warded off

Individual evidence

  1. ↑ Ordinance to combat Sharak disease
  2. ↑ http://www.artus-group.de/jojo.html

literature

  • Manfred Fischer: Color Atlas of Fruit Types (2nd edition), Stuttgart 2003 (among other things, classification of the types according to susceptibility to poultry)
  • Walter Hartmann : Color Atlas of Old Fruit Types. Eugen Ulmer, Stuttgart 2003 (including classification of varieties according to susceptibility to sharps)

Web links

Commons : Sharka  - collection of images, videos and audio files