Frost Resistance in Eucalyptus : a New Method for Assessment of Frost Injury in Altitudinal Provenances of E. viminalis

Abstract

Seedlings of E. viminalis were grown under controlled environment conditions and exposed to single frost treatments between - 1 and -5°C. A new objective method for assessment of frost injury was developed on the basis that killed leaf tissue lost water until equilibrium was established with atmospheric moisture. The percentage ratio of dry weight to wet weight was found to increase &om; 30% for unaffected plants to 85% for killed plants, and intermediate values provided a reliable quantitative assessment of the severity of intermediate injury.

There was no clear relationship between frost resistance and growth rate. Frost resistance increased with increase in altitude of seed source above 1000 ft, but the sea level provenance proved to be as frost-resistant as the provenance at 3600 ft, which suggested that more than an altitudinal cline for frost resistance is involved. Further- more, variation in frost resistance within half-sib families and within provenances was often significant and of the same order as the variation between provenances. Thus frost resistance in E. viminalis appears to involve several different mechanisms. Within-provenance and within-family variability was characterized by a low frequency of plants with intermediate injury, and the implications of balancing selection between susceptible and resistant phenotypes as one possible mechanism for this, are discussed.