Revisiting Cold Hardiness of Peaches in Georgia

Temperature plays a leading role in limiting plant distribution on Earth. Critical bud freezing temperature is the temperature at which buds are injured or lethally damaged by low temperature. The knowledge of this critical freezing temperature can help peach growers determine and avoid potential economic loss before and after a freeze. The objective of this study was to revisit the critical bud freezing temperature of two peach cultivars, ‘Elberta’ (850 chill hour) and ‘Flavorich’ (700 chill hour), and to study various techniques to determine the critical bud freezing temperature through the winters of 2014-2015 and 2015-2016 in Fort Valley, GA. A traditional freezing test was used to determine the freezing tolerance of floral buds, vegetative buds, and stems. Samples of excised floral and vegetative buds, 5 cm stems, and 20 cm stems, were evaluated for visual damage after controlled freezing experiments. The controlled freezing test was conducted at a freezing rate of 4°C/h and within a temperature range of -3°C to -27°C. Critical bud freezing temperature was determined as the lethal bud temperature at 50% mortality (LT₅₀). Across the two years, difference in cold hardiness was reported among cultivars (P<0.0001). ‘Elberta’ flower buds were significantly hardier than ‘Flavorich’. Both cultivars developed cold hardiness in the fall during the cold acclimation stage, and reached the maximum levels of cold hardiness around Jan 28 in both years. Cold hardiness decreased after late January, with ‘Flavorich’ cold deacclimation occurring quicker and blooming earlier than ‘Elberta’. Excised flower and vegetative buds had higher critical bud freezing temperature when compared to their counterparts still attached to the stems (P<0.0001). Stem cold hardiness was maintained even after floral buds deacclimated. The results provided will help to better understand the mechanisms that peaches use to survive low temperature. The information presented will aid to compare and to understand new techniques that could be used to better determine the critical bud freezing temperature of peaches and help growers with real time information for upcoming freezing events.