Differential Thermal Analysis of ‘Elberta’ and ‘Flavorich’ Peach Flower Buds to Predict Cold Hardiness in Georgia

in HortScience

Differential thermal analysis (DTA) has great potential as a quick and convenient cold hardiness determination method in plants. It measures freezing events inside of plant samples by detecting exotherm(s) produced when water changes from liquid to solid phase. DTA is highly sensitive to the experimental conditions and it has been reported to be ineffective among different fruit crops after acclimation of floral buds has occurred. The objective of this project was to establish DTA as a rapid and accurate method to predict peach floral bud cold hardiness from acclimation to deacclimation as compared with the traditional standard artificial freezing test. Floral buds of ‘Elberta’ and ‘Flavorich’ peach cultivars were subjected to DTA and artificial freezing tests throughout the winters of 2015–16 and 2016–17. Before deacclimation, two distinct exotherms, low-temperature exotherms (LTE) and high-temperature exotherms (HTE), were normally detected from floral bud DTA analyses. After deacclimation, DTA tests yielded only a few LTEs. However, incubation of floral buds at −2 °C overnight before the cooling process of DTA tests yielded an increased number of LTEs for both seasons in comparison with samples directly run using DTA without incubation. Similarly, after deacclimation started, the temperature in which LTE occurred was correlated (r = 0.59–0.86) with LT50 (lethal temperature that damaged 50% of floral buds) when DTA samples were treated overnight at −2 °C. In our study, pretreatment of floral buds at −2 °C overcame the inability of DTA to detect LTEs after deacclimation, which improved the ability and reliability of DTA to detect LTEs for more than 50% of the buds used per date per cultivar. DTA is a promising method to predict cold hardiness of peach plants.

Contributor Notes

This project was funded by the Florida Specialty Crop Block Grant USDA/FDACS No. 021759.

This paper is a portion of a thesis by Jun Liu in fulfilling degree requirement for the University of Georgia. The authors thank Malgosia Florkowska and Oliff Weldon for their help, Pearson Farm for allowing us access to their commercial orchards, and the Georgia Peach Council and the Georgia Agricultural Commission for Peaches for their support.

Corresponding author. E-mail: dchavez@uga.edu.

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    Examples of differential thermal analyses (DTA) profiles of one thermoelectric module (TEM) during DTA tests. High-temperature exotherms (HTEs) and low-temperature exotherms (LTEs) can be distinguished by their shapes and locations. HTEs were observed at higher temperature (closer to positive values in the x-axis), and were wider than the LTEs. DTA profiles changed when tests were performed with different cultivars, bud stages, and DTA cooling schemes (with or without pretreatment). Acclimated floral buds of ‘Elberta’ (A, B) and ‘Flavorich’ (E, F) were collected on 26 Jan. 2016, and tested with both “regular DTA” (A, E) and with “pretreatment DTA” (B, F) for each cultivar, respectively. Deacclimated floral buds of ‘Elberta’ (C, D) and ‘Flavorich’ (G, H) were collected on 7 Mar. 2016, and similarly were subjected to both “regular DTA” (C, G) and DTA with “pretreatment” (D, H) for each cultivar, respectively. Symbol * denoted LTE peaks in the DTA profiles. Dmv = differential millivolts.

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    Examples of temperature distribution of exotherm fitted by JMP Pro13. Samples were collected on 26 Jan. 2016. Forty-eight ‘Flavorich’ floral buds were tested for each test. Left: Normal 2 Mixture distribution of exotherms detected by regular DTA. Right: Normal distribution of exotherms detected by pretreated DTA.

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    Variation of critical bud temperature (LT50) and temperatures of LTE from both DTA tests through time. Artificial freezing test and DTA were performed on ‘Elberta’ (A, B) and ‘Flavorich’ (C, D) through the winter season of 2015–16 (A, C) and winter season of 2016–17 (B, D). Temperatures of LTEs from regular DTA were noted as “LTEregular” and temperature of LTEs from pretreated DTA were noted as “LTEpretreated.”

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    Seasonal fluctuation of water content in floral buds of ‘Elberta’ and ‘Flavorich’ in the winter season of 2015–16 (A) and winter season of 2016–17 (B). Bud water content was expressed as percentage of floral bud fresh weight.

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