Apple fruit rot can be caused by several fungi. In Northern Europe, the most common storage rot, Bull’s eye rot, is caused by Neofabraea spp., bitter rot by Colletotrichum spp., brown rot by Monilinia fructigena, grey mould is caused by Botrytis cinerea and Fusarium rot by several Fusarium species. Blue mold decay caused by Penicillium expansum is an important disease in several European countries. Incidence of different causal agents may vary depending on cultivar, climate during growing season and agricultural practices. The main objective of the study was to obtain baseline information about apple rot-causing fungi, their incidence during fruit storage and to evaluate the fungicide sensitivity of most of isolated fungal species. The study was performed during the storage period of apples after the growth season of 2013. Rotten apples were sorted in the storage and part of them was brought to the laboratory in order to obtain fungal isolates. Fungi were identified according to the morphological characteristics and sequencing of the ITS1-5.8S-ITS2 region. During storage in February and March the total percentage of rotten apples in various cultivars varied from 3.6 to 58.9%. All post-harvest diseases described in Northern Europe were detected. In part of the storehouses apple rot caused by Cadophora luteo-olivacea was observed. Alternaria spp. and Cladosporium spp. were detected on few apples as secondary infection agents. Using the most often isolated fungal species, sensitivity tests were performed against five commonly used fungicides. In general, the sensitivity of tested fungi to the fungicides was high with exception of several Neofabraea and Alternaria isolates.

The apple scab induced by Venturia inaequalis is an economically significant disease of apples worldwide and is predominantly controlled by multiple fungicide applications. Therefore, resistant apple cultivation is important for long-standing disease control. The knowledge about cultivar resistance is mainly founded on their evaluation in orchard conditions and testing in a greenhouse that is laborious and requires a large space. This study evaluated apple cultivar resistance and the virulence of V. inaequalis strains by inoculating detached leaves and immature fruits. Nine V. inaequalis strains originating from different apple-growing regions and host genotypes were tested on eight apple genotypes. Microscopic and macroscopic symptom development and host tissue reactions were monitored during the experiments. The tested V. inaequalis strains and cultivars showed different levels of virulence and resistance, respectively. Cultivar ‘Lobo’ was scored as partially susceptible, with almost all strains tested. The incompatible interaction with or without host tissue reactions was observed only on the cultivar ‘Priscilla’ with all the strains and field populations tested. The results of this study using detached leaves and immature fruits were concordant with the data obtained in the cultivar evaluation trials in the orchards..