Genetic variances and covariances for frost tolerance in Eucalyptus globulus and E. nitens

Controlled- and open-pollinated families of Eucalyptus globulus subsp. globulus (referred to here as E. globulus) and E. nitens, were tested for frost resistance at 3 test temperatures (−5.5 °C, −7.0 °C and −8.5 °C) using the electrical conductivity method. Additive, dominance and error variance and covariances were estimated using a derivative-free restricted maximum likelihood (DFREML) procedure and heritabilities, genetic and phenotypic correlations were calculated. E. nitens was more frost tolerant than E. globulus, the former being largely undamaged at −8.5 °C. E. globulus control-pollinated material (GCP) was tolerant to −7.5 °C but was severely damaged at −8.5 °C. Open-pollinated E. globulus from both seed orchards (GSOP) and natural stands (GOP) was severely damaged at −7.0 °C with the 50 % damage criteria probably met at about −6.0 °C. Heritabilities were moderate to high for both species, ranging from 0.29 to 0.50 for GCP and 0.23 to 0.44 for E. nitens control-pollinated material (NCP). It is suggested that estimates of heritability from E. globulus open-pollinated families from native stands (GOP), with values ranging from 0.53 to 0.61, are over-estimated due to the effects of selfing and neighbourhood inbreeding. Estimates of heritability for open-pollinated families from seed orchards in both specics (GSOP and NSOP) were similar to corresponding control-pollinated families (GCP and NCP, respectively) suggesting that removal of selfing and other inbreeding effects have occurred. Genetic correlations between relative conductivity at different temperatures were high, suggesting the same genes arc involved despite differing levels of damage