Fusarium circinatum, the causal agent of pine pitch canker (PPC), is currently one of the most important threats of Pinus spp. globally. This pathogen is known in many pine-growing regions, including natural and planted forests, and can affect all life stages of trees, from emerging seedlings to mature trees. Despite the importance of PPC, the global distribution of F. circinatum is poorly documented, and this problem is also true of the hosts within countries that are affected. The aim of this study was to review the global distribution of F. circinatum, with a particular focus on Europe. We considered (1) the current and historical pathogen records, both positive and negative, based on confirmed reports from Europe and globally; (2) the genetic diversity and population structure of the pathogen; (3) the current distribution of PPC in Europe, comparing published models of predicted disease distribution; and (4) host susceptibility by reviewing literature and generating a comprehensive list of known hosts for the fungus. These data were collated from 41 countries and used to compile a specially constructed geo-database. A review of 6297 observation records showed that F. circinatum and the symptoms it causes on conifers occurred in 14 countries, including four in Europe, and is absent in 28 countries. Field observations and experimental data from 138 host species revealed 106 susceptible host species including 85 Pinus species, 6 non-pine tree species and 15 grass and herb species. Our data confirm that susceptibility to F. circinatum varies between different host species, tree ages and environmental characteristics. Knowledge on the geographic distribution, host range and the relative susceptibility of different hosts is essential for disease management, mitigation and containment strategies. The findings reported in this review will support countries that are currently free of F. circinatum in implementing effective procedures and restrictions and prevent further spread of the pathogen.

Resistance to the pandemic strain of Austropuccinia psidii was identified in New Zealand provenance Leptospermum scoparium, Kunzea robusta, and K. linearis plants. Only 1 Metrosideros excelsa-resistant plant was found (of the 570 tested) and no resistant plants of either Lophomyrtus bullata or L. obcordata were found. Three types of resistance were identified in Leptospermum scoparium. The first two, a putative immune response and a hypersensitive response, are leaf resistance mechanisms found in other myrtaceous species while on the lateral and main stems a putative immune stem resistance was also observed. Both leaf and stem infection were found on K. robusta and K. linearis plants as well as branch tip dieback that developed on almost 50% of the plants. L. scoparium, K. robusta, and K. linearis are the first myrtaceous species where consistent infection of stems has been observed in artificial inoculation trials. This new finding and the first observation of significant branch tip dieback of plants of the two Kunzea spp. resulted in the development of two new myrtle rust disease severity assessment scales. Significant seed family and provenance effects were found in L. scoparium, K. robusta, and K. linearis: some families produced significantly more plants with leaf, stem, and (in Kunzea spp.) branch tip dieback resistance, and provenances provided different percentages of resistant families and plants. The distribution of the disease symptoms on plants from the same seed family, and between plants from different seed families, suggested that the leaf, stem, and branch tip dieback resistances were the result of independent disease resistance mechanisms.

Austropuccinia psidii (myrtle rust) was first detected on mainland Aotearoa (New Zealand) in 2017 and has established in various urban areas and native forests. To understand the spread of this pathogen and its effect on host species, surveillance for myrtle rust on Myrtaceae in native forests was undertaken in central Te Ika a Māui (North Island). In one site, with confirmed A. psidii infection, the rust infected up to 90% of new flush stem and leaves of some ramarama and rōhutu (Lophomyrtus spp.), with the pathogen eventually causing dieback of these shoots. The rust also infected developing fruit, causing it to prematurely drop, and infected all seedlings monitored in the site. It is likely that heavily infected trees will die and natural regeneration of Lophomyrtus spp. is unlikely; localised extinction is probable. Other Myrtaceae species in the stand, white rātā (Metrosideros diffusa) and mānuka (Leptospermum scoparium), were also infected but the severity of infection was less on these species than observed on Lophomyrtus spp. However, the long-term impact on these species from increasing or sustained disease pressure is unknown. Highly infected plants had decreased insect activity and diversity, highlighting the multi-tropic risk this invasive disease poses. A second site, approximately 15 km from known infected areas, which also contained Lophomyrtus spp., remained myrtle rust-free, showing that spread of this disease across landscapes is variable. This is the first monitoring study of myrtle rust on native forests in New Zealand. Continued monitoring is critical to provide information for effective management of this disease.

Austropuccinia psidii, cause of myrtle rust, has spread globally where Myrtaceae occur. Multiple strains of A. psidii have been identified, including a unique strain found only in South Africa. The South African strain is a biosecurity concern for species of Myrtaceae worldwide. This is because preliminary testing of South African Myrtaceae suggests it could have a wide host range, and thus has the potential to be invasive. In this study, we assessed the ability of the South African strain to infect other species of Myrtaceae by testing the susceptibility of New Zealand provenance Myrtaceae. Seedlings of four native New Zealand Myrtaceae species (Metrosideros excelsa, Leptospermum scoparium, Kunzea robusta, and Kunzea linearis) were artificially inoculated in South Africa with a single‐uredinium isolate of the South African strain. Fourteen days after inoculation, uredinia, and in many cases telia, had developed on the young leaves and stems of all four host species, which led to shoot tip dieback in the more severe cases. When comparisons were made between the species, K. robusta was the least susceptible to the South African strain of A. psidii, while L. scoparium and M. excelsa were the most susceptible. While only a limited number of seed families were tested, only a small proportion of the seedlings showed resistance to infection by the South African strain. This preliminary testing highlights the potential invasive risk the South African strain poses to global Myrtaceae communities, including New Zealand Myrtaceae.

Current forest biosecurity systems and processes employed in many countries are, in large, constructs of Western principles, values and science knowledge that have been introduced and integrated internationally. They are often devoid of knowledge, and of the values and principles, held by indigenous people, even those who have an intimate and enduring relationship with their forests. Indigenous people are also often overlooked in policy and decision-making processes, yet are often most affected by biosecurity pests and pathogens that impact native plant species that they may rely on for sustenance, cultural or spiritual purposes. By adopting an inclusive approach, scientists and indigenous people can achieve more comprehensive and robust biosecurity outcomes through a shared diversity of knowledge and at the same time serves to elevate and recognise the importance of indigenous knowledge. A co-innovation approach can also result in more widespread adoption of tools or practices by end-users including indigenous people. Understanding New Zealand Māori and their unique knowledge base can help improve forest biosecurity systems and practices, as can discussions of barriers that can and have prevented adoption of inclusiveness. Here we outline key principles behind indigenous engagement, specifically the need to develop enduring relationships.