Submitted to: Acta Horticulturae
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/3/2004
Publication Date: 4/20/2005
Citation: Postman, J.D., Spotts, R.A., Calabro, J.M. 2005. Scab resistance in pyrus germplasm. Acta Horticulturae. 671:601-608. Interpretive Summary: Pear scab, caused by the fungus Venturia pirina, causes economic losses due to unmarketable fruit and increased costs for application of fungicides in most of the world’s pear growing regions. A genetically diverse group of 200 pear varieties was selected from the 1800 that are maintained at the USDA-ARS germplasm repository in Corvallis to be evaluated for resistance to scab. Small potted trees were inoculated with scab spores in the greenhouse, and the incidence of resulting infections was recorded. Orchard trees were also evaluated over a ten year period for natural infections. Some varieties were severely affected by scab, and others were almost entirely free of symptoms year after year. Asian pear varieties in general were found to be very resistant to pear scab in western Oregon. This study has identified pear varieties that may be grown without chemical scab control. These pear varieties may be useful for breeders to use as parents to help develop new pear varieties that are resistant to scab.
Technical Abstract: 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, and grown under greenhouse conditions ideal for infection. Orchard trees were evaluated during 10 years for natural fruit scab (FS), and during 3 years for percent of leaves with leaf scab (LS). FS was rated on a scale of 1 to 9 (1 = no scab). Only 34 clones produced leaf symptoms following greenhouse 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.