Molecular detection of Venturia inaequalis in apple to monitor strobilurin resistance and inoculum size in air, leaf and fruit samples

Apple scab, caused by Venturia inaequalis, is the most important disease in apples in temperate climates. Scab not only attacks the tree but also the fruits, which leads to huge economic problems. The management of apple scab today consists of the removal of leaf litter at the end of the season, treatments for fast decomposition of leaf litter and treatments with fungicides. More and more a warning system is being used in which the potential infection risk is calculated. When there is a risk for infection by ascospores (primary infection), warnings are send out. This way farmers can treat their plants when there is an actual risk. Though infections are less severe, farmers still observe scab. This project strives to improve this warning system.  

A first element in this project is to develop a method to assess the potential ascospore dose before the start of the season. On the one hand we do this by quantification of scab in leaves and on the other hand by early induced discharge of spores from leaf material. We will try to correlate this with the actual discharge which is monitored by spore traps on top of leaves sampled at leaf fall and by spore traps in the field. A comparison is made between two different spore traps and between quantification of spores through molecular and microscopic techniques.

A second element of this project is to determine the level of resistance of the initial scab population to strobilurin.

Last but not least we will attempt to understand the evolution of scab, mainly latent scab, in apple and leaf material during autumn and winter.