CHARACTERIZATION OF COLD HARDINESS IN QUINCE: POTENTIAL PEAR ROOTSTOCK CANDIDATES FOR NORTHERN PEAR PRODUCTION REGIONS
The USA 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 in the USA and Canada. Fifty in-situ clonal quince accessions with diverse origins, and seven Pyrus clones, located at the USDA clonal genebank have been screened monthly (September-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 × Farmingdale Pyrus clones widely used today in the USA.
Einhorn, T.C., Turner, J., Gibeaut, D. and Postman, J.D. (2011). CHARACTERIZATION OF COLD HARDINESS IN QUINCE: POTENTIAL PEAR ROOTSTOCK CANDIDATES FOR NORTHERN PEAR PRODUCTION REGIONS. Acta Hortic. 909, 137-143
Cydonia oblonga, cold hardiness, pear rootstock, differential thermal analysis