ISHS Acta Horticulturae 151: III International Workshop on Fire Blight
RECENT ADVANCES IN THE USDA PEAR BREEDING PROGRAM |
| Authors: | R.L. Bell, T. van der Zwet |
| Abstract:
The pear breeding program of the United States Department of Agriculture was originated to develop pear cultivars with a high degree of resistance to fire blight (Erwinia amylovora [Burr.] Winslow, et al.). Current advanced selections are 3–5 generations removed from the original sources of resistance in Pyrus communis L. Additional resistant germplasm has been incorporated from P. ussuriensis, P. pyrifolia, and P. calleryana. Resistance to pear psylla (Psyllapy ricola Foerster) has been added as a major objective of the program. Growth habit studies have been initiated with the goal of breeding for productive scion cultivars of genetically reduced stature. To date, 4400 seedlings from controlled pollinations have been planted in single rows 2×5 m apart. All seedlings are routinely inoculated in the greenhouse in May and screened for fire blight resistance. Only about 10–20% are planted from the greenhouse to the nursery where they are inoculated again in late June. All seedlings with no more than 10% of the plant blighted are transplanted to the field in November. The trees are maintained on a 8-year rotation schedule and data are collected on tree growth characteristics, quality and yield of fruit as well as incidence of fire blight, Fabraea leaf spot and, for selected crosses, pear psylla. A second planting at Wooster, Ohio, is being maintained for an additional screening of cultivars, seedlings, and selections. Today, the 4 most superior advanced selections are under final testing. These selections appear to have a moderate to high degree of fire blight resistance combined with good fruit quality. At the U.S. Plant Introduction Station in Glenn Dale, Maryland, germplasm introductions, collected in Yugoslavia, Romania, and Poland, are under observation for disease and insect resistance. To date, about 10% have been lost to fire blight, whereas about 25 accessions, mainly from Yugoslavia and Romania, appear to have a high degree of resistance to leaf spot and psylla. The most superior germplasm soon will be incorporated into the breeding program. | |
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