Location: National Clonal Germplasm RepositoryTitle: Characterization of cold hardiness in quince: potential pear rootstock candidates for northern pear production regions Author
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2011
Publication Date: 10/31/2011
Citation: Einhorn, T., Turner, J., Gibeaut, D., Postman, J.D., Mota, J., Williams, R. 2011. Characterization of cold hardiness in quince: potential pear rootstock candidates for northern pear production regions. Acta Horticulturae. 909:137-143. Interpretive Summary: Quince is the most widely used rootstock worldwide for producing dwarf pear trees. When pears are grown on trees grafted to quince rootstock, the trees produce fruit at an earlier age and fruit production per acre is much greater than on other rootstocks. Quince rootstocks are not used, however, in the important pear production areas of northern Oregon and Washington because this genus is considered to lack cold hardiness. This study evaluated the cold hardiness of a large and diverse collection of quince varieties maintained at the USDA clonal genebank in Oregon. Quince cuttings were collected monthly from September through March, and stem pieces were subjected to freezing temperatures in a growth chamber and then evaluated for damage. While some quince selections were found to be sensitive to winter temperatures just below freezing, others were very hardy and were not damaged by temperatures between -20 and -40 Fahrenheit when fully dormant in mid-winter. Not only were many quince selections much more cold-tolerant than expected, they achieved full hardiness at different times during the season. Some were more cold hardy in November, others in January or February. The diversity of freeze-tolerance found in different quince varieties will help to select and develop improved dwarfing rootstocks for growing pears in colder production areas, and improve fruit production for this crop.
Technical Abstract: The US pear industry lacks a size-controlling, precocious rootstock for pear production. Commercially available selections of quince (Cydonia oblonga Mill.) have been reported to possess insufficient cold tolerance for northern latitude sites. Fifty in-situ clonal quince accessions with diverse origins, and seven Pyrus clones, located at the USDA clonal genebank in Oregon were screened monthly (Sept – March) to characterize their response to acclimation/de-acclimation conditions, determine minimum hardiness level, and identify tissue-specific sensitivity limits to sub-zero temperatures. One-year-old shoot pieces were loaded into a programmable freeze chamber, and subjected to freezing at a rate of 4° C per hour. Samples were removed following one hour at each of five treatment temperatures (0, -10, -20, -30, and -40 °C), incubated at 20 °C for one-week, sectioned transversely, and observed under a stereomicroscope. Individual tissue zones (phloem, cambium, and xylem) were rated according to the degree of oxidative browning. The lowest exposure temperature sustained with minimum observable tissue injury (< 25 % browning) was used to report minimum hardiness level. Ambient temperatures (minimum and mean) recorded at the genebank gradually declined throughout early fall, providing good conditions for onset of cold acclimation and development of hardiness. Following cold acclimation, 25 quince accessions were capable of withstanding -30 °C without detectable levels of freeze injury. Thirteen of those were categorized as having low levels of tissue browning (likely survivability) following exposure to -40 °C. Under our climatic conditions, none of the pear accessions tested, including four previously reported cold-hardy accessions, appeared capable of withstanding -40 °C. Sensitivity to sub-zero temperatures was similar among xylem, phloem and cambial tissue, though phloem tended to possess slightly greater hardiness during December (peak hardiness period). Several quince clones exhibited freeze tolerance equal to or greater than the current ‘Old Home’ x ‘Farmingdale’ Pyrus clones widely used today in the US.