RESEARCH ON FROST HARDINESS OF PINUS CONTORTA SEEDLINGS GROWN IN CLIMATE CHAMBERS

An artificial testing of hardiness in seedlings of Pinus contorta was performed by means of freezing plants to -10°C following treatment with successively prolonged nights (4 &rarrow; 16 h) and lowered night temperatures (+5°C). The photoperiod was the main factor controlling the hardening process – hardiness increased with increasing night lengths.
However, low night temperatures (below +10°C) also promoted the development of hardiness.

Three characters correlated with hardiness were identified – intensity of anthocyanin colour and dry-matter content in the upper-most 3 cm of shoots, which were positively correlated with hardiness, and elongation of secondary needles, a character that proved to be negatively correlated with hardiness, the latter being used as a criterium of hardiness in early tests.

Twelve populations originating from the latitudinal range 47–63°N showed a clinal variation in hardiness.
After the same photoperiodic treatment, the northern populations attained a higher degree of hardiness than the southern ones.

Good agreement was obtained between the frequency of severely damaged plants after artificial freezing and mortality at 5 years age in field trials, in which populations from the same latitudinal range were included.

Significant differences in frost hardiness among single-tree progenies originating from open pollinated plus trees within one stand at 57°N were revealed.

II Symposium on Winter Hardiness in Woody Perennials

A. Jonsson

https://doi.org/10.17660/ActaHortic.1985.168.10