© 1995 Heron Publishing—Victoria, Canada
Temperature control of the development of frost hardiness in two populations of Leptospermum scoparium
Dennis H. Greer and Linda A. Robinson
Plant Physiology Group, Horticulture and Food Research Institute, Private Bag 11030, Palmerston North, New Zealand / Received March 24, 1994
Summary
Seedlings of Leptospermum scoparium J.R. et G. Forst (manuka) originating from seed from a low altitude coastal site (Auckland) and from a high altitude inland
site (Desert Road) were grown for 96 days in four controlled environments to compare the relationship between growth temperature
and frost hardening. Day/night temperature treatments were 12/6, 12/3, 12/0 and 12/–3 °C. Frost hardiness was determined at
14-day intervals by exposing whole seedlings to temperatures ranging from –2 to –8 °C. Frost damage differed significantly
between the two populations: Desert Road seedlings were less affected than Auckland seedlings. At all growth temperatures,
the time courses of frost hardiness of both populations followed curvilinear relationships reaching a maximum hardiness at
about Day 50, after which the seedlings spontaneously dehardened. The rate of frost hardening increased linearly with decreasing
temperature from 6 to 0 °C, but thereafter, no further increase occurred with decreasing temperature to –3 °C. The frost hardening
process was more sensitive to temperature in the Desert Road seedlings than in the Auckland seedlings, and this difference
may account for the intraspecific variation in frost hardening capacity of this species. Comparisons with Pinus radiata D. Don and Lolium perenne L. indicated that interspecific variation in frost hardening capacity can also be accounted for by differences in the sensitivity
of the hardening process to temperature.
Keywords:
controlled environment, dehardening, manuka, Myrtaceae.
