Growth, Form and Quambalaria Shoot Blight Tolerance of Spotted Gum in North-eastern New South Wales, Australia

A young provenance/progeny trial of spotted gums, which are major hardwood plantation species in subtropical eastern Australia, was studied for growth, form, and damage from Quambalaria shoot blight. The trial contained a wide range of genotypes, mainly of Corymbia citriodora subsp. variegata, with between one and 21 families per provenance. Genetic parameters were calculated from 23 provenances with four or more families. Provenances superior for growth included four well-represented C. citriodora subsp. variegata provenances, all from south-east Queensland, which also had a high proportion of superior families. Overall, Queensland provenances had significantly higher mean diameter and height than those from New South Wales (NSW), although there were several superior NSW families. Provenances superior for growth also displayed good straightness and relatively fine branching. Relatively low Quambalaria shoot blight damage was recorded for four Queensland provenances and one coastal NSW provenance, which all had high proportions of families with low damage. Provenances that were putative intergrades between C. citriodora subsp. variegata and C. maculata tended to have high damage levels. However, some mediocre provenances contained superior families potentially useful for breeding. Regressions of Quambalaria damage index (QDI) on latitude, and mean height growth on QDI, were highly significant and moderately strong (0.51 and 0.58, respectively), indicating increasing damage in more southern material, and a retarding effect (although not striking) of damage on growth. Individual heritability estimates were low (zero to 0.14) for growth and form, and moderate for QDI (0.31). The genetic correlations for QDI with growth traits were strong and negative (-0.77 and -0.88), supporting a strategy of selecting vigorous trees for breeding programs from provenances and families superior for these traits.