Phenotypic and Molecular Screening of Apple Genotypes to Woolly Apple Aphid Resistance

Abstract

Woolly apple aphid (WAA) is a major pest of apple orchards resulting in significant losses. In the present study, 22 apple (Malus domestica Borkh.) cultivars were tested in the filed for their relative resistance/susceptibility to WAA. These apple cultivars were found to respond differentially to WAA infestation. Based on tree infestation rating, cultivars were ranked into 6 relative resistance/susceptibility groups, as follows: immune - ‘Golden Delicious’, ‘Delbarestivale’, ‘Golden Smoothie’, ‘Red Miracle’ and ‘Harmony’; resistant - ‘Stark Gold’, ‘Early Gold’ and ‘Argi Gala’; moderately resistant - ‘Evanee’ and ‘Black Stayman’; moderately susceptible - ‘Vista Bella’, ‘Jonagold’, ‘Royal Gala’, ‘Jersey Mac’, ‘Granny Spur Type’ and  ‘Summerred’; susceptible - ‘Jonathan’, ‘Nagava 6’, ‘Florina’, ‘Red Chief’ and ‘Gold Iralis’; highly susceptible - ‘Fuji 6’. Eight molecular markers linked to major WAA resistant genes (Er1, Er2, and Er3) were screened in apple cultivars using PCR. The markers NZms_EB145764, NZms_EB106753 and NZsc_E01 were ubiquitous in all cultivars under study, whereas, NZsn_O05 was absent. The results of other markers revealed distinct patterns of amplification among apple cultivars. No clear correlations can be made between the molecular data (marker presence and absence) and the phenotypic results (cultivar ranking). The differences among cultivars regarding WAA infestation can potentially be utilized by apple breeders and commercial growers to achieve effective, environmental-friendly, and low-cost pest control.