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

Abstract

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.

Genetic control of flowering in spotted gum, Corymbia citriodora subsp. variegata and C. maculata

“…Shoot blight damage caused by QSB has a major effect on the crowns of planted CCV because the lesions and distortion of new shoots, including stems and expanding leaves, can cause a massive reduction in foliage, or loss of apical dominance in severe cases (Pegg et al 2011). Northern populations were found to be more tolerant to damage caused by QSB in the Bonalbo trial (Johnson et al 2009) and this may account for the larger size of trees from these populations in the current study. However, the productivity of CM is usually greater when it is grown in temperate regions where QSB is unlikely to be significant, due to a drier climate (Arnold et al 2005).…”

“…Evidence is mounting that populations of CCV differ in potentially important adaptive traits such as disease tolerance (Johnson et al 2009;Pegg et al 2011), frost tolerance (Larmour et al 2000), terpene chemistry (Asante et al 2001) and peak flowering time (this study), reflecting natural selection among populations for particular genes and gene combinations. Gene flow between populations may contribute to either mal-adaption (e.g.…”

“…The trial has been described in detail in Johnson et al (2009). In brief, it contained a wide collection of CCV as well as some CM provenances (Fig.…”

“…1). It was established in 1999 on an ex-grazing site with an east-facing aspect and an infertile yellow podzolic soil and receives a mean annual rainfall (MAR) of 1031 mm (Johnson et al 2009; Australian Bureau of Meteorology 2012). It was laid out using a randomised complete block design (RCBD) with five replicates of 196 open-pollinated families planted in five-treeline plots; only four replicates were assessed in this study as one replicate had poor survival by 2009.…”

“…bloodwoods) to gene flow from locally exotic taxa that are inter-fertile (Barbour et al 2008). In recent years, commercial plantations of CCV have been derived from one or a few select provenances in the north of its range, particularly Woondum provenance near Gympie, Qld, which is genetically and adaptively differentiated both from the CCV and CH provenances from NSW including its higher tolerance to Quambalaria shoot blight (QSB) (Johnson et al 2009;Brawner et al 2011).…”