Relationships among bud dormancy status, cold hardiness, and stress resistance in 2+0 Douglas-fir

Abstract

An experiment was conducted to ascertain what relationships might exist among dormancy status, cold hardiness and stress resistance in 2+0 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), seedlings. Seedlings were lifted from a western Washington nursery on six dates spanning the 1980–81 lifting season. On each date samples of seedlings were subjected to the following treatment: (1) tumbling for 5 minutes, (2) desiccation of roots for 30 minutes at 30°C and 2.1 kPa vapor pressure deficit, (3) exposure of shoots to temperatures of −10°C, −15°C or −20°C for two hours and (4) unstressed control. On two lift dates sub-samples of seedlings were placed into −1°C storage and held for two months before the above stress treatments were administered. Bud dormancy status was determined, using a bud break test, on seedlings from each lift date before and after storage.

After one growing season in the field percent survival, vigor, height growth and shoot and root weight were determined on stressed and unstressed seedlings. Survival and vigor were less affected by the stress treatments than were height and weight. Severity of stress was in the order −20°C > −15°C > desiccation > handling > −10°C. Degree of cold injury was directly related to seedling dormancy status whether dormancy status had been attained in the nursery from natural chilling or in frozen storage. Seedlings in a mid-range of dormancy release (between deep rest and quiescence) were most resistant to all imposed stresses.