2017 ASHS Annual Conference

Reduction in fruit production due to cold damage in floral tissues is the biggest single limitation to profitability and ultimately survival in the Colorado peach industry. The physiological mechanisms that impart peach floral buds cold hardiness, and their interaction with weather events are complex and poorly understood. This study aimed to identify the critical temperatures of peach buds during the different phases of dormancy as well as during dormancy release, bud-break and bloom phenology. Cold hardiness, expressed as lethal temperature for 10% (LT₁₀), 50% (LT₅₀), or 90% (LT₉₀) of peach buds was quantified successfully with differential thermal analysis (DTA) and the standard cold exposure method for assessing cold damage based on oxidative browning. Three peach cultivars including ‘Sierra Rich’, ‘Cresthaven’ and ‘Red Haven’ were tested during the late fall to early spring season of 2016-2017. High temperature exotherms (HTE), that created from the freezing event of the super cooled extracellular water and characterized as nonlethal, were identified for the different peach cultivars during the early stages of bud development early in fall. DTA analysis showed that the temperature causing freezing injury was related to the initiation of the low temperature exotherms (LTE’s) after October 21^st. Cold hardiness followed a predictable seasonal pattern in all three cultivars: an acclimation phase in late fall, a period of maximum hardiness in winter (mid December- late January), and deacclimation going into spring. Temperature fluctuations, however, lead to considerable “noise” in this general trend. Sudden freezing events induced hardiness and unseasonal warm temperatures induced temporary deacclimation in peach buds. Differences in hardiness were found for all the peach cultivars that were evaluated as well as between different sampling dates. ‘Sierra Rich’ was the least hardy and showed minimum response to freezing events and deacclimated faster as a response to unseasonal warm temperatures, compared to the other cultivars tested. DTA analysis successfully predicted a 15% bud damage on ‘Sierra Rich’ on January 6^th. During bud swell, DTA was not an effective method for detecting LTE in peach buds. However, incubating buds at -2°C for 12 h before DTA run shifted the LTE appearance and this approach was highly correlated with the LT₅₀ calculated by oxidative browning. During bud-break and bloom phenology cold tolerance was estimated with the standard oxidative browning method. The information that was generated in this study will provide a better understanding of peach cold hardiness and will support growers in decision-making of frost control practices and estimate potential losses.