Incidence of races of the apple scab pathogen (Venturia inaequalis) in apple growing districts in Sweden

The incidence of the physiological apple scab races 1-7 was determined in Swedish apple growing districts between 1999 and 2002. Thirteen apple cultivars, selections or Malus species grafted on rootstock B9 were used as indicator plants. The plants were divided into three lots: one was planted in the field, one was used for growth chamber/greenhouse experiments and one was potted and used as a portable screening orchard. Plants in the growth chamber experiments were inoculated with conidial suspensions (2-3x10(5) conidia ml(-1)) from different parts of Sweden. Three weeks after inoculation, the apple scab symptoms were assessed. Race 1 was found in all experiments, while race 5 was absent. Race 4 was only found in samples from the southeastern locations Balsgard and Kivik. The presence of apple scab on Malus baccata jackii was observed in several places for the first time in Sweden. In the orchard trial (Kivik, southeast Sweden, 2001-2002), the trees were interplanted with the susceptible cultivar 'Mutsu'. During the second year, races 1-4 and lesions on M. baccata jackii were found. The portable screening orchard was used as a new method for detection of apple scab races. The indicators were placed in an old, unpruned orchard at Alnarp in 2002. Races 1-3 were observed, plus scab lesions on M. baccata jackii. This method might be feasible for future detection of apple scab races. In conclusion, the apple scab races 1-4 and 6-7 were found in different parts of Sweden while race 5 was absent. Race 7 was observed for the first time in Sweden.