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Several species from the genus Quambalaria (order Microstromatales) cause diseases on eucalypts (Eucalyptus and related genera) both in plantations and natural ecosystems. We developed real-time quantitative PCR (qPCR) assays to rapidly detect and distinguish five Quambalaria species. The design of the species-specific qPCR assay for each species, Q. pitereka (PIT), Q. coyrecup (COR), Q. cyanescens (CYN), Q. pusilla (PUS), and Q. eucalypti (EUC), was based on the ITS region and was evaluated for specificity and sensitivity. The PIT, COR, and CYN qPCR assays could amplify as little as 10 fg µl−1 from pure cultures, whereas PUS and EUC qPCR assays could amplify 100 fg µl−1 of their target species. The PIT, COR, and CYN qPCR assays were further validated using naturally and artificially infected samples of their plant host Corymbia calophylla. These assays will be used for rapid diagnostics and future experiments on the infection process.

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.