Quambalaria shoot blight resistance in marri (Corymbia calophylla): genetic parameters and correlations between growth rate and blight resistance

Quambalaria shoot blight (QSB) has emerged recently as a severe disease of Corymbia calophylla (marri). In this study, QSB damage and growth were assessed in Corymbia calophylla trees at 4 and 6 years of age in two common gardens consisting of 165 and 170 open-pollinated families representing 18 provenances across the species’ natural distribution. There were significant differences between provenances for all traits. The narrow-sense heritability for growth traits and QSB damage at both sites were low to moderate. The genetic correlation between QSB damage and growth traits was negative; fast-growing families were less damaged by QSB disease. Age-age genetic correlations for individual traits at four and six years were very strong, and the type-B (site–site) correlations were strongly positive for all traits. Provenances from cooler wetter regions showed higher resistance to QSB. The QSB incidence at 6 years was significantly correlated with environmental factors of the provenance’s origin. The QSB incidence at years four and six was not correlated with the QSB expression in 3-month-old seedlings. Based on these results, selection for resistance could be undertaken using 4-year-old trees. There is potential for a resistance breeding program to develop populations of marri genetically diverse and resistant to QSB.