PRELIMINARY SCREENING OF APPLE GERMPLASM FOR RESISTANCE TO SILVERLEAFINFECTION

As effective control measures for silverleaf (caused by Chondrostereum purpureum) are lacking, the breeding and selection of resistant culti vars is considered the most effective means of combatting the disease. In this paper the results of preliminary evaluation of apple germplas m for silverleaf resistance are presented. Cuttings of 214 apple (Malu s spp.) cultivars, advanced selections, and rootstocks were artificial ly inoculated with a single isolate of C. purpureum. After 1 month inc ubation in vitro the depth of xylem staining was measured and used as an assessment of resistance. Cuttings of 23 cultivars were unaffected by the fungus, whereas the xylem tissues of cuttings of 24 cultivars a nd sports were fully stained. The wide range of the mean depth of xyle m staining implied that silverleaf resistance is polygenic. However, t he high levels of resistance of the cultivar 'Northern Spy' and some o f its derivatives indicated major gene resistance in the cultivars.