2017 ASHS Annual Conference

Cold hardiness survival is one of the key limiting factors for growing and breeding woody ornamental plants in the Northern Great Plains. There are three factors involved with cold hardiness: wood hardiness (vegetative structures), flower-bud hardiness (reproductive structures) and root hardiness. Cold hardiness survival of ornamental species including Magnolia have been ongoing by the North Dakota State University Woody Plant Improvement Program (NDSU WPIP). The Magnolia cold hardiness survival evaluations from the NDSU WPIP found that there is a high amount of variability among species and cultivars from the subgenera Yulania for cold hardiness survival. Several cultivars (‘Ballerina’, ‘Merrill’, ‘Leonard Messel, ‘Royal Star’, and ‘Yellowbird’) have survived but have limited performance with regard to either wood or flower-bud cold hardiness. In conjunction with field trials, electrolyte conductivity freeze-tests measure cold hardiness survival based on the rate of electrolyte leakage among different reproductive and vegetative tissues including flower-bud, vegetative-bud, and stem segments. A factorial of species and cultivars (‘Ballerina’, ‘Merrill’, ‘Leonard Messel, ‘Royal Star’, ‘Centennial’ ‘Yellowbird’, and M. xsoulangeana), tissue (flower-bud, vegetative-bud, and stem), and temperature (-24, -32, -36, -40, -44 °C) were used to determine species percent injury by tissue type at each subsequent temperature. Prior to freezing, explants were cut into 5mm segments with 0.2mL deionized water, 2mg silver iodide, and placed in plastic vials. Vials were kept in refrigerator over night at 4°C to create homogeneity. After 24h, vials were placed in a timely programed freeze chamber. Once temperatures (-24, -32, -36, -40, -44 °C) were met, vials were placed on a shaker for 1h and measured electrolyte conductivity. Explants experienced heat kill in a chamber at 95°C for 1.5h, placed on shaker for 1h, and measured electrolyte conductivity. Tissue percent injury was determined by the equation: 100*(CI - CR) / (1 - CR), where CI is the cold injury ratio at each subsequent temperature and CR is the control ratio. Ratios were determined by control, cold injury, and heat kill electrolyte readings. Preliminary data concluded percent injury remains constant for stem, vegetative-bud, and flower-bud segments across temperatures. Flower-bud percent injury shows the least amount of damage followed by vegetative-bud and stem segments. Therefore, flower-bud electrolyte conductivity protocols should be re-established for accurate readings. Magnolia xsoulangeana (M. denudata x M. liliiflora, saucer magnolia) as expected, shows the most damage for each tissue type at all temperatures, concluding electrolyte conductivity tests viable for further research.