Variation in frost tolerance of the 1,8-cineole-rich variants of the peppermint eucalypts, Eucalyptus radiata and E. dives

Abstract

Summary Frost tolerance is a necessary characteristic for the successful establishment of Eucalyptus radiata subsp. radiata Sieber ex DC (1,8-cineole variant) for production of essential oil on frost-prone sites. The frost tolerance of seedlings from six commercial oil- producing provenances of this taxon was examined using the electrical conductivity method. One provenance of E. radiata subsp. robertsonii and two provenances of E. dives Schauer were also included for comparison. To verify the validity of this method, frost tolerance was also assessed in two field trials near Armidale on the New England Tableland of New South Wales where plants at one year from planting were scored for physical damage attributed to the effects of frost, viz. leaf fall and stem splitting. There were consistent and significant differences in modified relative conductivity (RC) between provenances, and between open-pollinated families within provenances, across temperatures. Eucalyptus radiata subsp. radiata from Isabella River, followed closely by provenances from Reedy Creek and Yowrie, were the most cold-tolerant, while the two E. dives provenances and E. radiata subsp. radiata from Alexandra were the least frost tolerant, based on RC values. Rankings of E. radiata subsp. radiata provenances based on scores for stem splitting and leaf fall after their first winter in the field corresponded well to the RC rankings, with Reedy Creek the best performing provenance overall. Apart from limiting frost damage through selection of hardy provenances, the significant within-provenance family variation in frost tolerance, and the substantial variation between individuals within families noted in these trials, suggest good potential for selection and breeding amongst hardy individuals of the best- ranked families to improve frost tolerance.