Comparing methods to determine European canker resistance in apple tree accessions

Abstract

Pruning cuts made in summer and pruning cuts leaf scars and score wounds made in autumn were inoculated to compare their suitability to discriminate for European canker resistance among apple accessions When pruning cuts were inoculated in summer the mean lesion size varied between accessions with Royal Gala displaying significantly larger lesions than 15 other accessions 17 to 43 days after inoculation (P<0001) Robusta 5 (R5) and M9 had the smallest lesions 43 days after inoculation When pruning cuts were inoculated in autumn R5 displayed the smallest lesions among 12 accessions 4 and 10 months after inoculation while M9 Royal Gala and Granny Smith had significantly larger lesions than R5 (P<0001) Inoculated score wounds of Granny Smith and Jonathan developed significantly smaller lesions than those of M9 (P<0001) When leaf scars were inoculated Jonathan developed symptoms on only 10 of the leaf scars and lesions were significantly smaller than in other accessions (P<0001) Royal Gala had the largest lesions and 56 of leaf scars of M9 developed symptoms This study has shown that the expression of the disease in various accessions differs according to the method and timing of inoculation