Variation in low temperature exotherms of pecan cultivar dormant twigs

Authors: Volk, Gayle; Waddell, John; TOWILL, LEIGH - Retired ARS Employee; Grauke, Larry

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2008
Publication Date: 4/1/2009
Citation: Volk, G.M., Waddell, J.W., Towill, L., Grauke, L.J. 2009. Variation in low temperature exotherms of pecan cultivar dormant twigs. HortScience. 44:317-321.

Interpretive Summary: Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees native to northern regions are more cold tolerant than those native to and grown in the southern United States. To identify a possible assay for cold hardiness, dormant winter twigs from 112 pecan cultivars were surveyed using differential thermal analyses. Signals that can sometimes be correlated with cold hardiness were identifiable when twigs were stored at -3ºC for up to 120 days after harvest. Thirty-nine percent of the southern pecan cultivars lacked a signal and the remaining southern cultivars had temperature signals of -32.9 ºC. In contrast, only 11% of the northern pecan cultivars lacked the temperature signal and the remaining cultivars had a significantly lower temperature signals -35.4ºC, even though twig samples were collected from trees grown in the same Texas orchard, suggesting that there is a genetic component that affects the temperature signals that could predict cold hardiness. Budbreak data was also collected for diverse pecan cultivars, and budbreak occurred earlier in southern cultivars than those that originated in the north. Both budbreak and temperature signal data can be correlated with regional origin, and it is suggested that budbreak may be a preferred indicator to predict relative cold hardiness in pecan.

Technical Abstract: Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees native to northern regions are more cold tolerant than those native to and grown in the southern United States. To identify a possible assay for cold hardiness, dormant winter twigs from 112 pecan cultivars were surveyed using differential thermal analyses. The low temperature exotherm (LTE) from differential thermal analyses was identifiable when twigs were stored at -3ºC for up to 120 days after harvest. Thirty-nine percent of the southern pecan cultivars lacked a LTE, and the remaining southern cultivars had an average LTE of -32.9 ºC. In contrast, only 11% of the northern pecan cultivars lacked the LTE and the remaining cultivars had a significantly lower LTE of -35.4ºC, even though twig samples were collected from trees grown in the same Texas orchard, suggesting that there is a genetic component that affects the temperature of the LTE. Budbreak data was also collected for diverse pecan cultivars, and budbreak occurred earlier in southern cultivars than those that originated in the north. Both budbreak and LTE data can be correlated with regional origin, and it is suggested that budbreak may be a better indicator than DTA to predict relative cold hardiness in pecan.