Using the Electrolyte Leakage Method to Determine Freeze Tolerance in Peach Fruitlets

Late freezes cause fruit crop losses worth millions of dollars in the U.S. annually. In many fruit tree crops like peaches, a decrease of a few degrees can mean a complete loss of fruit, and although critical temperatures for the different development stages are well known, there are varietal differences in the temperatures that cause seed abortion and fruit loss. In this study, we set up a protocol to use the electrolyte leakage method for determining in-vitro lethal freezing temperatures of peach fruitlets. We tested three different protocols: 1) using fruitlet slices; 2) using fruitlets cut in half; and 3) using whole fruitlets. For each protocol, we used fruitlets from four different cultivars. Samples were placed in test tubes with deionized water, and immersed in a refrigerated water bath with decreasing temperatures between 0 and -10 C at two-degree intervals. Every hour, we took out three replicate test tubes per cultivar and measured electrical conductivity (EC1). After introducing all the samples in an autoclaved at 121 C for 20 min, electrical conductivity was measured again (EC2). Then, we estimated electrolyte leakage as EC1/EC2 (%) and plotted it against decreasing temperatures. Our results showed that the use of whole fruitlets can be successfully used for determining lethal freezing temperatures and for performing comparisons between different cultivars. However, the test tubes with fruitlet slices or fruitlets cut in half did not performed as well as the ones with the uncut fruitlets.