Apple scab
| Apple scab | ||||||||||||
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Infested apple |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Venturia inaequalis | ||||||||||||
| ( Cooke ) G. Winter |
The apple scab ( Venturia inaequalis ) is one of the most important apple tree diseases worldwide and is caused by the hose fungus Venturia inaequalis . The secondary crop form is called Spilocaea pomi .
features
The infestation shows itself on the leaves with dull olive green, later brown or blackish spots, which can flow together and form larger necroses as a result, which leads to premature leaf loss of the trees. The fruits usually have darker colored spots, in which mostly star-shaped cracks appear, which serve as a gateway for putrefactive agents such as Monilia . This affects the shelf life of the fruit . However, the fruits themselves can be consumed without hesitation. Young shoots can also be infected.
The primary infection of the host takes place in spring from the sick leaves of the previous year lying on the ground, on which the pseudothecia had formed up to the time of the leaves appearing . They have small dark hairs around the opening and contain pseudo paraphyses . When the weather is good, such as high humidity, eight two-celled ascospores are actively ejected from the asci and reach the host with the wind. There the ascospores germinate under favorable conditions (10 to 20 hours of wetness at 10 to 20 ° C), for example on wet leaves, and infect the host. The first symptoms appear after one to three weeks.
The fungus and thus the disease spread in summer through the conidia , which are formed in large numbers in the area of the spots and necroses. They are primarily splashed by the rain.
ecology
The apple scab needs a high level of moisture and therefore attacks leaves and fruits with a lot of rainfall, especially in spring and summer . A precise infestation forecast is possible. This means that the time for the prophylactic use of fungicides to prevent the disease can be optimally determined.
infection risk
Whether an infection occurs depends on the temperature and time.
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activities
In cultivation
In addition to choosing the variety, there are a number of preventive measures that can at least reduce the infestation. On the one hand, the fallen leaves are reduced by spraying the leaves with leaf fertilizers or by breaking up the fallen leaves by mulching . On the other hand, good ventilation and faster drying of the leaves are ensured by the way in which the tree canopy is cut and the way it is raised, which influences the infection conditions of moisture and temperature. By promoting the early termination of shoots, new infections on young, sensitive leaves are prevented well into late summer. In organic farming are as direct actions sulfur and copper compounds such as copper oxychloride as pesticides approved.
Resistance breeding
Classic breeding
The susceptibility to scab depends on the variety. Several mono- and polygenic resistance genes are known. Efforts have been made since the middle of the 20th century to cross the cultivated apple with resistant Malus varieties and to use them to breed scab-resistant varieties. In scab, the sources of resistance from Antonovka (Va), Hansen's baccata (Vb), Malus baccata jackii (Vbj), Malus floribunda (Vf), Malus micromalus (Vm) and Malus pumila (Vr) are known. Up to now, Malus floribunda has been the main tool for this purpose . Resistant apple varieties such as “ Florina ”, “ Liberty ”, “ Rewena ”, “ Retina ”, “ Reanda ”, “ Remo ”, “ Topaz ” and others come from these breeding programs . The often crossed monogenic Rvi6 (formerly Vf) resistance gene comes from the wild apple line Malus floribunda 821 . In individual cases, its resistance has already been broken by the pathogen. Modern breeding is therefore based on pyramidizing several uninterrupted resistance genes in order to ensure a more stable, long-lasting resistance. It does this by re-crossing an offspring of a susceptible variety and a resistant variety with a resistant variety whose resistance is based on a different gene. After several backcrosses with good quality varieties, a new variety with two or more resistance genes can be produced, which meets the quality requirements on the market. However, due to the long juvenile phase of the apple, this process takes up to 25 years. Up to 2009, 600 different apple varieties were tested for susceptibility to scab in a research project in Switzerland.
Genetic engineering
Both cisgenic and transgenic methods are used to shorten the breeding of new robust varieties . With the cisgenic method, resistance genes from wild apples are inserted directly into existing varieties (e.g. Royal Gala ). Because this resistance gene comes from a natural cross partner, the cisgenic variety could also be bred by classic breeding. The genome of these varieties therefore comes completely from the apple. By using the cisgenic method, the cultivation time can be significantly reduced. The second method that is used is transgenic flowering early. A birch gene is used in the breeding material, which causes the apple tree to flower a few months after sowing. As a result, the juvenile phase and the breeding time are shortened by up to 95 percent. The cultivated variety does not contain the transgene in the end, since in the last step after crossing transgenic with normal apples only genotypes are selected that do not flower prematurely.
proof
- Venturia inaequalis. In: Wood diseases in words and pictures. Faculty of Forest Science and Resource Management at the Technical University of Munich, archived from the original on June 10, 2007 ; Retrieved February 20, 2010 .
- Wolfgang Kreckl: Apple scab (Venturia inaequalis). In: Articles from the Institute for Plant Protection. Bavarian State Research Center for Agriculture, accessed on September 18, 2015 .
Remarks
- ↑ Fruit growing manual of the fruit growing research institute Jork , 2011
- ↑ Defense mechanisms and resistances in pome fruit. In: Fachinformationen. State teaching and research institute for viticulture and fruit growing in Weinsberg, online at LVWO-bw.de, accessed on February 9, 2017.
- ↑ Bernhard Koller, Cesare Gessler et al .: Technological consequences of the use of genetically modified disease-resistant crops - part apple. Technical study of the consequences of technology apple. Eidgenössische Forschungsanstalt für Obst-, Wein- und Gartenbau Wädenswil, Zurich October 12, 1995, from BATS.ch, accessed on February 9, 2017 (PDF; 351 kB).
- ↑ Hans-Jakob Schärer, Markus Kellerhals: Scab breakthrough in Vf-resistant apple varieties? In: Swiss journal for fruit and wine growing. Edition 7, 2000, on Agroscope.admin.ch, accessed on February 13, 2017 (PDF; 224 kB), pp. 124–126.
- ^ M. Kellerhals, T. Székely, C. Sauer, JE Frey, A. Patocchi: Pyramidization of scab resistance in apple breeding . In: Commercial fruit growing . tape 51 , no. 1 , February 2009, p. 21–28 , doi : 10.1007 / s10341-009-0078-3 ( PDF ).
- ↑ T. Visser: Juvenile Phase and Growth of Apple and Pear Seedlings . In: Euphytica . tape 13 , no. 2 , 1964, doi : 10.1007 / bf00033299 ( PDF ).
- ↑ Claudia Rindt: The guardians of the fruit rarities. In: Südkurier. September 29, 2007, from Suedkurier.de, accessed on February 13, 2017.
- ↑ Scab-resistant apples - With genetic engineering to the "organic apple"? At Pflanzen-Forschung-Ethik.de, accessed on February 13, 2017.
- ↑ Henryk Flachowsky, Pierre-Marie Le Roux, Andreas Peil, Andrea Patocchi, Klaus Richter, Magda-Viola Hanke: Application of a high-speed breeding technology to apple (Malus × domestica) based on transgenic early flowering plants and marker-assisted selection . In: New Phytologist . tape 192 , no. 2 , October 2011, p. 364 , doi : 10.1111 / j.1469-8137.2011.03813.x (English, libgen.io [PDF; 1,2 MB ; accessed on February 13, 2017]).
