SCAB RESISTANCE IN PYRUS GERMPLASM

The 1800 Pyrus clones at USDA-ARS-NCGR-Corvallis represent world diversity for pears. A “core” subset of 31 Asian cultivars, 119 European cultivars, 8 hybrid cultivars, and 45 species selections was evaluated for resistance to pear scab caused by Venturia pirina Aderh. Three potted, grafted trees of each core accession were artificially inoculated in a glasshouse. Orchard trees were evaluated during 10 years for natural fruit scab (FS), and during 3 years for leaf scab (LS). FS was rated on a scale of 1 to 9 (1 = no scab). Only 34 clones produced leaf symptoms following glasshouse inoculation, however 24 of these also rated high for natural LS in the field. All Asian cultivars were nearly free of both FS and LS. No Asian cultivar had a mean FS rating greater than 4, and 42% had no scab or negligible ratings. Thirty-eight percent of European cultivars had mean FS ratings >4, and 8% had no scab or negligible scab. Average LS incidence was 3.4% of leaves for European cultivars compared to 0.4% for Asian cultivars. More than 64% of European cultivars had >1% LS. European cultivars with negligible FS and LS include ‘Arganche,’ ‘Batjarka,’ ‘Brandy,’ ‘Erabasma,’ ‘Muscat,’ and ‘Passe Crassane.’ Incidence of both FS and LS in hybrid cultivars was intermediate between that of Asian and European cultivars. Most species selections had negligible FS, except P. cordata with a rating of 5. Of 23 European cultivars rated high for FS, 21 also had >1% LS. This study has identified pear cultivars that may be grown without chemical scab control, and that may be useful as parents in breeding for resistance.