GENETIC VARIANCES AND COVARIANCES FOR FROST TOLERANCE IN EUCALYPTUS-GLOBULUS AND EUCALYPTUS-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 degrees C, -7.0 deg rees C and -8.5 degrees C) using the electrical conductivity method. A dditive, dominance and error variance and covariances were estimated u sing a derivative-free restricted maximum likelihood (DFREML) procedur e and heritabilities, genetic and phenotypic correlations were calcula ted. E. nitens was more frost tolerant than E. globulus, the former be ing largely undamaged at -8.5 degrees C. E. globulus control-pollinate d material (GCP) was tolerant to -7.5 degrees C but was severely damag ed at -8.5 degrees C. Open-pollinated E. globulus from both seed orcha rds (GSOP) and natural stands (GOP) was severely damaged at -7.0 degre es C with the 50% damage criteria probably met at about -6.0 degrees 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 val ues ranging from 0.53 to 0.61, are over-estimated due to the effects o f selfing and neighbourhood inbreeding. Estimates of heritability for open-pollinated families from seed orchards in both species (GSOP and NSOP) were similar to corresponding control-pollinated families (GCP a nd NCP, respectively) suggesting that removal of selfing and other inb reeding effects have occurred. Genetic correlations between relative c onductivity at different temperatures were high, suggesting the same g enes are involved despite differing levels of damage.