Apple scab
Afflicted apple
The apple scab (Venturia inaequalis) is one of the most important apple tree diseases worldwide and is caused by the ascomycete Venturia inaequalis. The secondary fruit shape is called Spilocaea pomi.
Features
The infestation is evident in the leaves with matt olive green, brown or blackish spots later that can flow together, and subsequently form larger necrotic tissue, which leads to premature defoliation of the trees. The fruits usually have darker colored spots, where most star-shaped cracks that serve as Monilia rot pathogens as portal of entry. Thus the storage life of the fruit is impaired. However, the fruits themselves can be safely consumed. Even young shoots can be infected.
The primary infection of the host takes place in the spring, of the fallen diseased leaves of the previous year, on which up to the time of sprouting leaves have formed the pseudothecia. They have small dark hairs around the opening and contain Pseudoparaphysen. With favorable weather conditions such as high humidity, eight two-celled ascospores from the asci are actively ejected and go with the wind on the host. There, the ascospores germinate under favorable conditions (10 to 20 hours wetness at 10 to 20 ° C), for example, wet leaves and infect the host. The first symptoms appear after one to three weeks.
The propagation of the fungus, and thus the disease occurs in summer by the conidia formed in the area of stain and necrosis in large numbers. They are sprayed primarily through the rain.
Ecology
The apple scab requires high humidity and therefore affects particularly in the early years and summers with lots of rainy leaves and fruits. An accurate forecast infestation is possible. Thus the time for the prophylactic use of fungicides to prevent the disease can be determined optimally.
Measures
In cultivation
Besides the choice of the variety, there are a number of preventive measures that can reduce the infestation, at least. On the one hand, the fall foliage can be reduced by foliar spraying with fertilizers or shredding of fallen leaves by mulching. On the other hand, is backed by cutting education and form a good aeration and rapid drying of the leaves, the infection conditions of moisture and temperature are affected. By promoting an early conclusion also drive new infections be prevented in young sensitive leaves until well into the late summer. In organic farming are authorized as pesticides as direct actions sulfur and copper oxychloride.
Resistance breeding
Susceptibility to Schorfpilze is dependent on the type. Since the end of the 20th century, we are endeavoring to cross the cultivated apple with resistant Malus varieties, and from this to breed resistant varieties. These previously served mainly Malus floribunda. From these breeding programs are taken from resistant varieties such as Florina, Liberty, Rewena, retina, Reanda, Remo, Topaz, and others. The resistance comes mainly from the wild apple Malus floribunda line 821 In individual cases, however, it was already broken.
Evidence
- Template: Internet resource / maintenance / access date is not in the ISO FormatVenturia inaequalis. Study Faculty of Forest Science and Resource Management at the Technical University of Munich, accessed on 20 February 2010.
- Template: Internet resource / maintenance / access date not in ISO format template: Internet resource / Maintenance / date not in ISO format Wolfgang Kreckl: apple scab (Venturia inaequalis). In: Articles from the Institute of Plant Protection. Bavarian State Research Center for Agriculture, February 2007, accessed on 20 February 2010.