Breeding apples for scab tolerance at Holovousy

Summary

There are 53 apple cultivars registered for commercial growing in the Czech Republic, at present, from which 4 are resistant and 7 tolerant to scab (Venturia inaequalis/Cke/Wmt). There seem to be increasing demands especially for these tolerant cultivars in connection with the spread of integrated fruit growing systems. Therefore a majority of cultivars now released from Holovousy and being given to State Variety Trials belongs to this category. In addition to breeding apples with resistance to scab based on a single dominant gene derived from Malusfloribunda 821, the breeding programme in Holovousy has extensively utilized donors of polygenic resistance to scab for three generations. As donors mostly old and less known cultivars (‘Antonovka’, ‘Emneth Early’, ‘Hagloe Crab’, ‘Hájkova reneta’, ‘Reinette Rouge Étoilée’ and’ spätblühender Taffetapfel’) were used but to a lesser extent also some commercially grown cultivars (‘Bláhova oranžová’, ‘Glockenapfel’,‘James Grieve’, ‘Jonathan’, ‘Mio’, ‘Mother’ and some others). The presented segregation data are from material from three cycles of hybridization comprising 81 crosses and nearly 6,500 seedlings. These seedlings were preselected after early inoculations but the final rating was based on several severe spontaneous scab infections in orchards. No seedling was classified as immune. On average 3% of seedlings were evaluated as field resistant with the highest segregation of 21% in the cross ‘Hagloe Crab’ × ‘Emneth Early’. The group of seedlings rated as ‘tolerant’ (low susceptibility) segregated in frequencies averaging 10%, with a maximum of 41% for a single cross. From the first generations of the breeding programme at Holovousy 6 new apple cultivars (‘Angold’, ‘Julia’, ‘Klara’, ‘Nabella’, ‘Produkta’ and ‘Zuzana’) with a tolerance to scab have been recently released. Short descriptions are given.