Alternaria alternata
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Alternaria alternata with the typical pear-shaped conidia |
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| ( Fr. ) Keissl. (Fr.) |
Alternaria alternata is a fungus in the genus Alternaria . The species is a widespread decomposer ( saprophyte ) of organic materials in the soil . In addition, it can appear as a weak parasite on numerous wild and cultivated plants or as a mold colonize building materials and living spaces. As a pathogen he is z. B.relevantfor potatoes (spray stain disease) or cereals ( blackening fungi ).
biology
Alternaria alternata reproduces, like all species of the genus Alternaria, exclusively asexually. The mycelium forms septate conidial carriers individually or in small groups, which are somewhat shorter and thinner than in A. solani . The conidia form in long, partly branched chains, are darkly colored by melanin deposits and have a short beak that is no more than a third as long as the spore itself. Their shape is pear-shaped. In each conidia there are a maximum of eight transverse and several longitudinal septa.
The fungus as a household mold
Like many other saprophytes, Alternaria alternata can cause damage in buildings as a “mold”. It is one of many fungi that infest food, textiles, and wallpaper (wall mold). The mold toxins ( mycotoxins ) released in the process can cause allergies and damage to health. A. alternata forms, among other things , tenuazonic acid , Altenuen , tentoxin and alternariol .
Black fungus on cereals
The pathogen appears on cereals in interaction with other fungi such as Cladosporium or Epicoccum as a so-called black fungus. These do not infest vital plants, but colonize dead or ripened parts, where they feed on the already dead tissue. Significant symptoms are blackening (mold) of the affected areas. The damaging effect consists primarily in the formation of mold toxins, which can get into the crop and thus reduce its quality. Black fungi are combated with targeted fungicides.
Spray stain on potatoes
A. alternata often occurs in potatoes together with the closely related species Alternaria solani , which causes the symptomatically very similar dry spot disease. In the literature, both pathogens are usually treated together under the generic term "Alternaria disease in potatoes".
The pathogen has been known as a pathogen in potatoes for decades. Serious damage caused by him and A. solani has only occurred in Germany since the beginning of the 21st century. Since around 2010 (in NRW), large-scale monitoring projects and laboratory analyzes have been carried out in Germany to differentiate between the two pathogens.
Both pathogens have similar temperature requirements and development cycles. In conventional plant cultivation, they are usually combated with the standard treatment against late blight .
Symptoms
A typical symptom of the disease are numerous, tiny (maximum 5 mm) chocolate-brown necroses on the leaves (spray spots) that hardly grow after their formation. If the infestation is severe, the leaf mass is destroyed by the large number of spots. The spots are round to angular and always clearly demarcated from healthy tissue. The concentric ring structures typical of A. solani are hardly recognizable due to the small area of the spots.
The susceptibility of potatoes to A. alternata is very dependent on the variety. Since the disease often sets in in early summer, it has a damaging potential for all maturity dates.
Differentiation from dry spot disease
A. alternata and A. solani are often closely related and often occur simultaneously. The symptoms are also very similar, which is why a laboratory analysis is necessary for an accurate differentiation. In the field, however, the two species can be separated on the basis of a few characteristics: The dry spot disease generally occurs later. The main infection period usually begins, depending on the weather, from the end of August and thus up to eight weeks after the onset of A. alternata (from the end of May / beginning of June). In addition, infections by A. solani tend to form a few larger leaf spots (up to 2 cm) rather than many smaller ones. A. alternata does not attack the potato tubers, but has a much larger host of plants than A. solani , which is mainly restricted to species of the nightshade family .
research
The extract of Alternaria alternata shows in vitro antibacterial activity.
literature
- Horst Börner: Plant diseases and plant protection. (= UTB 518). 8., newly revised. and act. Edition. Verlag Eugen Ulmer, Stuttgart 2009, ISBN 978-3-540-49067-8 .
Web links
- lfl Bavaria, assessment of the harmful potential of Alternaria on potatoes , accessed on February 12, 2016
- lfl Bayern, Profile of Alternaria Disease in Potatoes , accessed on February 12, 2016
- Information on Alternaria Disease in Potatoes , accessed February 12, 2016
Individual evidence
- ↑ [1] , accessed on February 13, 2016.
- ↑ [2] , accessed on February 13, 2016.
- ↑ [3] , information from the North Rhine-Westphalia Chamber of Agriculture, accessed on February 12, 2016.
- ↑ Janeš, D., Umek, A., Kreft, S. (2006). Evaluation of antibacterial activity of extracts of five species of wood-colonizing fungi. J. Basic Microbiol., 46, 3: 203-207