Apple Scab Biology


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Apple Scab on leaves 

Apple Scab on fruits 

Apple Scab conidia 


Apple Scab Biology 

The disease "Apple scab", which is caused by the fungus Venturia inaequalis is one of the most economically important diseases worldwide. Apple scab occurs in every apple growing area worldwide. V. inaequalis is an obligate parasite, which means that it is only able to survive on green, fresh apple tissue. Under unfavourable conditions (no vegetation, during winter time) it survives in a stage of dormancy (fruit form, called ascocarp, pseudothecium) on leaves on the soil surface. Another form of hibernation of the fungus is in dormant pustules on shoots or buds. 

Pseudothecium (sexuell form) are formed in infected plant tissue at the end of the saison. They are 90-160 µm in diameter and can be seen with the naked eye or with a hand lens. After wintertime the diploid pseudothecium starts to form numerous asci each containing 8 ascospores. These ascospores are discharged by rain, wind and leaf wetness and are responsible for the infection of the green tissue of the apple trees. Water is one of the most important factors for fungal growth and reproduction, ascospores and conidia are germinating in free water. The germination tube forms an appressorium (pressure, enzyme) and enters the cuticle of the plant.  

For detailed information about the Discharge of spores see: See Apple Scab Ascospore discharge model.

For information of the infection by ascospores see: See Ascospore Infection Model and for infection by condia see: See Apple scab Conidia Infection Model. To learn how to use plant disease models for apple scab control read Practical use of the Apple Scab Models.


(c) Dr. Heinrich Denzer, Pessl Instruments GmbH, Weiz, 2007


Created by system. Last Modification: Wednesday 04 of March, 2015 11:00:25 GMT by cpilz.