Epidemiological research on the etiology of scab on pear

Abstract: Apple and pear scab, caused by Venturia inaequalis and V. pirina, respectively, are the key parasites in pome fruit growing. If no control measurements are undertaken, the pathogen can destroy a complete harvest when weather conditions are favourable. The scab fungi on pear and apple are two distinct species. Mostly they are considered to have a similar biological cycle. Despite the similarities, there are also clear differences and these differences are significant for the control of the pathogen. For example, pear scab does not only infect fruits and leaves as apple scab does, but also infects twigs. To better unravel the life cycle of the pear scab fungus and to develop a better control strategy a 4 year IWT (Agency for Innovation by Science and Technology)-funded research project was performed. In this project the etiology of pear scab, the diversity of V. pirina biotypes and their pathogenicity on different plant parts or cultivars and the scab management was investigated. The results of this project indicate that twig scab can be an important factor in the life cycle of pear scab and that plant part or type of cultivar does not always set up a barrier for cross infections with scab conidia. Genetic and molecular studies displayed, amongst others, that lesions are result of an infection of a single spore and that the scab fungus can be present asymptomatically on pear plant parts. Furthermore, our results indicated that infections of fruits occur already early in the season, but that the expression of the symptoms is delayed.