MR BIOLOGY REPORT: Myrtaceae vulnerability

Vulnerability of New Zealand Myrtaceae species to natural infection by Austropuccinia psidii (myrtle rust)

October 2021

Beresford R, Soewarto J, Somchit C, Hasna L, Ramos Romero L. 2021. Vulnerability of New Zealand Myrtaceae species to natural infection by Austropuccinia psidii (myrtle rust). PFR SPTS No. 21702. https://doi.org/10.34721/1v1s-qz14

ABSTRACT

Current knowledge about the vulnerability of New Zealand’s native myrtle species to A. psidii comes from resistance screening of young seedlings performed with artificial inoculation under controlled conditions, from surveillance data collected during the initial incursion response and from field observations. The controlled resistance screening is important because it can potentially reveal the inherent genetic susceptibility of species, whereas surveillance data and field observations may reflect sampling bias and other factors affecting vulnerability, such as presence of new shoot growth, presence of airborne spores (inoculum) and suitability of weather conditions. However, it needs to be determined how well the method of screening young seedlings under artificial conditions represents the effects of myrtle rust on host species in the natural environment.

This research established field trials in Rotorua and Auckland in spring 2019 to compare the artificial inoculation results with myrtle rust development at two sites where inoculum and environmental conditions were relatively uniform. Each trial contained five New Zealand native Myrtaceae species: ramarama (Lophomyrtus bullata), rōhutu (Lophomyrtus obcordata) pōhutukawa (Metrosideros excelsa), mānuka (Leptospermum scoparium) and kānuka (Kunzea robusta) and the exotic species, rose apple (Syzygium jambos), which is highly susceptible worldwide and was included to provide an international comparison.