INHERITANCE OF PARTIAL RESISTANCE TO APPLE SCAB IN TEN APPLE PROGENIES

Ten apple progenies were created using a 2×5 factorial mating design with the goal of studying the inheritance of partial resistance to apple scab (Venturia inaequalis). Two scab-susceptible breeding selections with good fruit quality (both of ‘Splendour’ × ‘Gala’ parentage) were used as seed parents and the following cultivars were used as pollen parents: ‘Gewurzluiken’, ‘Kardinal Bea’, ‘La Paix’, ‘Lubsk Queen’ and ‘Margil’. One hundred plants per family were planted in a randomized complete block design in a plot with a moist maritime climate at Agassiz, B.C., Canada. Commercial cultivars, parent clones and scab race indicators were included in the planting. No fungicides were applied. Scab severity was low over the whole planting in the first year of data collection (2009), but in 2010 and 2011, the weather was highly conducive to scab infection. Leaf scab symptoms were severe on susceptible commercial cultivars and a high proportion of the progeny plants. All of the pollen parent clones in the plot showed strong resistance to leaf scab each year, but the percentage of resistant progeny varied greatly among crosses. From 43 to 62% of the trees in both families with ‘Lubsk Queen’ as a pollen parent were either symptomless or showed low infection severity in 2010-2011. The results are discussed in the context of breeding for durable scab resistance.