Apple scab

Apple scab is a common disease of plants in the rose family (Rosaceae) that is caused by the ascomycete fungus Venturia inaequalis. While this disease affects several plant genera, including Sorbus, Cotoneaster, and Pyrus, it is most commonly associated with the infection of Malus trees, including species of flowering crabapple, as well as cultivated apple. The first symptoms of this disease are found in the foliage, blossoms, and developing fruits of affected trees, which develop dark, irregularly shaped lesions upon infection.

Although apple scab rarely kills its host, infection typically leads to fruit deformation and premature leaf and fruit drop, which enhance the susceptibility of the host plant to abiotic stress and secondary infection.
The reduction of fruit quality and yield may result in crop losses of up to 70%, posing a significant threat to the profitability of apple producers.
To reduce scab-related yield losses, growers often combine preventive practices, including sanitation and resistance breeding, with reactive measures, such as targeted fungicide or biocontrol treatments, to prevent the incidence and spread of apple scab in their crops.

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Source: Wikipedia · Image: Wikimedia Commons · CC BY-SA 3.0