Submitted to: Pear International Symposium
Publication Type: Abstract only
Publication Acceptance Date: 1/30/2004
Publication Date: 2/1/2004
Citation: Sardani, M., Spotts, R.A., Calabro, J.M., Postman, J.D. 2004. Evaluation of pyrus germplasm collection for resistance to powdery mildew [abstract]. Proceedings of the Pear International Symposium, February 1-5, 2004, Stellenbosch, South Africa. p. 38. Interpretive Summary: Powdery mildew, caused by the fungus Podosphaera leucotricha, 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 powdery mildew in the greenhouse, and the incidence of resulting infections was recorded. Trees were evaluated the following year following natural inoculations in an orchard. Some varieties were severely affected by mildew, and others were entirely free of symptoms in two different experiments. European pears were found to be more susceptible to powdery mildew than Asian pears. This study has identified pear varieties that may be grown without the use of pesticides to control mildew. We have also identified varieties that will be useful for breeders to use as parents to help develop new mildew resistant pear varieties.
Technical Abstract: Powdery mildew (PM), caused by the fungus Podosphaera leucotricha, occurs in most pear-growing areas of the world. PM causes economic losses due to reduced market value of russeted fruit as well as the increased need for fungicides. A recent study of PM resistance was done using the core Pyrus germplasm collection at NCGR-Corvallis, which consists of about 200 cultivars and species selections identified to represent most of the genetic diversity present of this crop. It includes 29 Asian cultivars (ASN), 107 European cultivars (EUR) as well as hybrids and pear species selections. Trees were evaluated for PM symptoms from natural field infections during 2003, by counting the number of leaves with symptoms on ten current year shoots. In 2001-2003, three trees of each core accession were grafted on potted seedling rootstocks, artificially inoculated in a greenhouse, grown under suitable PM conditions and evaluated for symptoms. EUR were overall more susceptible to PM than ASN, with 47% of EUR and 25% of ASN (field) and 93% of EUR and 43% of ASN (greenhouse) being infected with PM. Average PM incidence in the greenhouse (8% for ASN and 31% for EUR) was much higher compared to field infections (2% for ASN and 6% for EUR). In the field, 33% ASN and 38% of EUR with PM symptoms had a mean PM value of >10 . Symptoms were more severe in the greenhouse, with 62 ASN and 80 of EUR with PM symptoms having a mean PM value of >10 . Cultivars with consistent low PM ratings may have good promise for developing improved PM resistant cultivars in future pear breeding programs.