Fire blight resistance from 'Evereste' and Malus sieversii used in breeding for new high quality apple cultivars: strategies and results.

摘要

Apple breeders follow different strategies to bridge the gap of fire blight resistant cultivars with marketable fruit quality. At the research station Agroscope Changins-Wadenswil (ACW) in 2008, the advanced selection 'ACW 11303' was crossed with 'Evereste'. 'ACW 11303' carries resistance to scab (Rvi6, respectively Vf and Rvi4, respectively Vh4) and powdery mildew, and displays partial fire blight resistance and good fruit quality. 'Evereste' is an ornamental cultivar carrying an apple scab (Rvi6) resistance and a fire blight resistance QTL (Fb_E), but having small fruit size and poor fruit quality. Marker-assisted selection was used to screen the progeny for the combination of apple scab resistance genes as well as for Fb_E. Low input fast-track breeding was applied on selected genotypes in order to speed up the generation cycle. The plants were grown in a regular greenhouse establishing optimal growing conditions. Fourteen months after germination first flowers were formed by four plants out of 31. From flowering plants carrying the Fb_E QTL pollen was collected. Trees of the cultivar 'Topaz' were bagged and flowers manually pollinated with the above mentioned pollen at balloon stage and re-bagged until petal fall. Fruit was harvested in autumn, and subsequently seeds were extracted and stratified. The new generation will again be subjected to the low input fast-track breeding approach as soon as available. In order to find new sources of fire blight resistance to include in the Swiss breeding program, 12 Malus sieversii genotypes described as fire blight resistant and originating from Kazakhstan were inoculated with a Swiss strain of Erwina amylovora by injection. The results of the tested cultivars revealed large differences in susceptibility towards fire blight. The most resistant genotypes in the test were selected for crosses in 2010.