Soot Spot Disease

from Wikipedia, the free encyclopedia
Apples with soot stain. The fruit at the bottom right also shows an infestation by the fly pollution disease.

The sooty blotch is a plant disease of fruit. It is caused by a number of fungi and occurs worldwide in all regions with a humid climate during the growing season . In temperate and humid regions, it is one of the most common fungal diseases on apples . It develops its harmful effect by lowering the marketing value of the fruit.

description

The name of the disease is based on the appearance of the infected fruits: a black-green coating initially forms in individual spots on the skin. As the disease progresses, these spots can expand and cover the entire surface of the fruit until harvest. It is also possible to intensify the black coloring.

The damage pattern is similar to that of fly pollution, but it is caused by the fungus Schizothyrium pomi . In addition, both diseases often occur together on the same fruit. In English-speaking countries, they are usually addressed and treated together as sooty blotch and flyspeck (SBFS) or apple summer disease. Even in the German-language research literature, the name "Regenfleckenlkrankheit" is used both as a middle name for both clinical pictures and as a self-term for their combined occurrence.

It is unclear whether similar diseases in pears, bananas , papaya and persimmons are caused by the same mushrooms.

Pathogen

In research, numerous hose fungi are named as the causative agent of soot spot disease, including Phyllosticta solitaria , Peltaster fructicola , Geastrumia polystigmatis , Leptodontium elatius , Phyllachora pomigena , Gloeodes pomigena , Phialophora sessilis , Tripospermus camelopospermati and Tripospermus myrti . It has not yet been possible to clarify whether the fungi can individually cause the disease or whether they need to work together. Up to 60 pathogens are now associated with the disease. A large part of them is assigned to the class Dothideomycetes within the hose fungus, so they are closely related to the causative agent of apple scab .

A series of tests carried out by the Competence Center Fruit Growing - Bodensee in 2010 indicates that Peltaster fructicola is the main causative agent of soot stain and all other fungi associated with it could be insignificant.

Course of infection

Soot stain, like many other fungal diseases, is favored by damp weather with temperatures between 10 and 25 degrees Celsius. The first infections are observed in Central Europe shortly after flowering, but continue to occur throughout the summer. For the fungi to develop, the fruit needs about four hours of adhesive moisture. The dark coating becomes visible to the naked eye 30 to 40 days after infection.

A number of other plants are thought to be vectors. Pathogens were detected on apples from the previous year as well as on maple , linden and willow. Both the primary infection and the secondary infection between the fruits of an already infected plant occur via conidia and parts of the mycelium that are spread by wind and rain. The spatial expansion on individual fruits seems to be caused by rainwater running down, because the coating usually develops from top to bottom on the apple and in strips along drip channels. Older apple trees and varieties with only slightly colored skin (such as Golden Delicious ) appear to be particularly susceptible. Scab-resistant apple varieties are also affected by the soot stain disease.

The disease only affects the wax layer on the apple peel. There the fungus lives saprovor , i.e. exclusively on dead organic material, possibly on small amounts of fruit juice that escape through the skin. The gray spots appear around 20 to 25 days after infection, under weather conditions that are particularly favorable for the fungus with persistently high humidity and temperatures of around 20 degrees Celsius after around ten days.

Economical meaning

Soot spot disease has no impact on the health of the plant, nor on the development and food quality of the fruit. However, the covering, which can only be partially removed mechanically, means that the apples can hardly be sold in retail outlets.

Combat

As a preventive measure, choosing a sunny location away from typical foggy locations and an airy cut of the tree can reduce the moisture inside the tree canopy. A sufficiently large distance between the fruit trees and other trees make primary infection more difficult. Infested apples should be quickly removed from the crop by removing windfalls and fruit mummies and quickly transporting the harvest away. Because of the comparatively long time span between infection and visible occurrence, the economic damage is usually less for apple varieties with an early harvest date.

Fungicides that work against apple scab also fight soot stain. The covering can be partially removed by brushing and washing, thus improving its marketability. In countries where this is permitted, agents containing chlorine are added to the washing water.

A series of tests by the Competence Center Fruit Growing - Bodensee resulted in significantly reduced infections by shielding apple trees from the natural weather by means of foil roofs.

Research history

The American mycologist Lewis David von Schweinitz carried out what is believed to be the first microbial study of soot stain disease . In a publication from 1832 he named the pathogen as Dothidea pomigena (later: Gloeodes pomigena, today: Phyllachora pomigena). Since around the 1920s, English-language research has treated soot stain and fly grime together.

Since the end of the 20th century, in particular with the help of DNA sequencing , more and more types of fungus have been linked to the disease in rapid succession.

swell