Lowest Survival Temperature Estimation in 45 Magnolia Varieties by Controlled Freezing

Abstract

Lowest survival temperature (LST) estimations for 45 varieties of Magnolia from Delaware were obtained over 4 testing dates with some varieties tested on fewer dates due to a shortage of material. Terminal stem cuttings were subjected to a controlled freezing regime, incubated at 100% humidity for 10–14 days and evaluated for injury by visual observation. LSTs were estimated as the lowest temperature at which 100% survival was observed. LSTs were difficult to estimate due to a lack of consistency caused by fungal pathogens. Incubation in moist towels and aluminum foil, post-freeze addition of moist towels following prefreeze sodium hypochloride dip, and dry incubation were employed to eliminate fungal pathogenicity as a source of post-freeze damage. Results show varieties with M. ×loebneri heritage to be the most consistently cold tolerant. Varieties such as M. `Raspberry Ice' and M. `Merril' rated as inconsistent with no definite LST estimated. Direct comparisons of incubation method, date of test, fungal pathogenicity and varietal consistencies will be discussed.