DEVELOPMENTAL STAGES OF WINTERFAT GERMINANTS RELATED TO SURVIVAL AFTER FREEZING

Diaspores of winterfat (Eurotia lanata (Pursh) Moq.) collected from 2 locations in the USA and I in Canada were imbibed at 10 degrees C and grown to 4 different developmental stages (2, 3, 6, and 14 days of inc ubation), then subjected to cooling temperatures as low as -30 degrees C. Differential thermal analysis was used to detect exotherms associa ted with ice crystal formation in germinants, The temperature at which exotherms occurred was recorded, and the subsequent growth and mortal ity of germinants were determined. Only 1 exotherm was observed, and t hat occurred in the low-temperature exotherm range (usually < -10 degr ees C). Changes in the freezing tolerance of germinants from seed to s eedling was a gradual process as indicated by increases in exothermic temperature and mortality with increasing developmental stage. Whether the exotherm indicated a lethal event depended on the developmental s tage of the germinant, Germinant survival was also affected by cooling below the exotherm temperature.