Molecular diagnosis of <i>Puccinia psidii</i> (guava rust) – a quarantine threat to Australian eucalypt and Myrtaceae biodiversity

A species-specific, nested polymerase chain reaction (PCR)-based detection assay, using two primer sets designed from the rRNA ITS region, was developed for <i>Puccinia psidii</i>. Detection sensitivities of one urediniospore alone, or one or two urediniospores in the presence of pollen or leaf tissues, respectively, were observed. The assay reliably, accurately and sensitively detected the rust from naturally infected, geographically widespread eucalypt and fruit tree plantation and nursery species from diverse tissues types (e.g. leaves, flowers, fruits, pollen, seeds and woody material) including symptomless or cryptically contaminated plants or plant tissue. Independent testing in Brazil and Australia demonstrated the international inter-laboratory transferability of the <i>P. psidii</i> assay required for germplasm screening, disease monitoring and quarantine and incursion management, towards which the assay has already been employed.