Chasing myrtle rust in New Zealand: host range and distribution over the first year after invasion

Abstract

After the detection of the myrtle rust pathogen, Austropuccinia psidii, in New Zealand, a biosecurity response was initiated, including a widespread surveillance programme. Through an intensive public awareness initiative, the general public was highly engaged in reporting myrtle rust infections and added significant value to the surveys by reporting first detections from most of the areas that are now known to be infected. During the first year of the response, Austropuccinia psidii was found in areas that were predicted to be at high infection risk in previous modelling studies. Significant surveillance resources were deployed to different parts of the country and the response surveillance team contributed to most of the new host species finds. Twenty-four species and six hybrids of Myrtaceae have been confirmed to be naturally infected by myrtle rust in New Zealand. Eleven of these are new host records globally and three were previously recorded only as experimental hosts.

Using spatial models to identify refugia and guide restoration in response to an invasive plant pathogen

“…We found L. bullata and M. excelsa share similar climate (precipitation/temperature) tolerances to the disease (Figure 5; Appendix ) and therefore have limited refugia, even under the less‐extensive Scenario 1 (Figure 4a; Appendix ). Other species with limited refugia (<30% of their range) include M. albiflora , M. robusta and S. maire , but observed infection of these species to date is low (Toome‐Heller et al., 2020). Lophomyrtus obcordata has a greater tolerance of cooler temperatures, resulting in a larger proportion of its habitat acting as refugia (Figure 4c), which could be an in situ conservation tool for this species.…”

“…During surveillance immediately following the outbreak, myrtle rust was detected most frequently on L. bullata, L. obcordata and their hybrid, and also on M. excelsa (Toome-Heller et al, 2020); and a recent study found these species have little resistance across genotypes (Smith et al, 2020). We found L. bullata and M. excelsa share similar climate (precipitation/temperature) tolerances to the disease ( Figure 5; Appendix S9) and therefore have limited refugia, even under the less-extensive Scenario 1 (Figure 4a; Appendix S8).…”

“…We found L. bullata and M. excelsa share similar climate (precipitation/temperature) tolerances to the disease ( Figure 5; Appendix S9) and therefore have limited refugia, even under the less-extensive Scenario 1 (Figure 4a; Appendix S8). Other species with limited refugia (<30% of their range) include M. albiflora, M. robusta and S. maire, but observed infection of these species to date is low (Toome-Heller et al, 2020). Assessment to ensure refugia will remain effective under future climates should also be considered (Ashcroft, 2010;Harris, Hobbs, Higgs, & Aronson, 2006), especially for populations marginally outside the risk area that could become vulnerable.…”

“…diminished recruitment rates from reduced seed production, or inability to recover from disturbance following repeat infection of epicormic growth (Pegg et al., 2018). Of the 27 Myrtaceae trees, shrubs and vine species native to New Zealand, the endemic genus Lophomyrtus (two species) is considered most susceptible to infection (Beresford, Smith, Ganley, & Campbell, 2019; Beresford et al., 2018; Toome‐Heller et al., 2020). The genera Syzygium , Metrosideros and Leptospermum are also affected.…”

Monitoring Austropuccinia psidii (myrtle rust) on New Zealand Myrtaceae in native forest

“…Austropuccinia psidii is native to South America (Coutinho et al 1998) but multiple strains of this pathogen have spread worldwide during the last few decades (Stewart et al 2017) and it is now regarded as a globally invasive pathogen threatening native Myrtaceae, Myrtaceae-related economies, and ecosystems (Pegg et al 2017). The pandemic biotype (Stewart et al 2017) of A. psidii was first detected on mainland Aotearoa (New Zealand) in May 2017 in Kerikeri (du Plessis et al 2019; Guy & Barry 2017) but was rapidly found in other regions across Te Ika a Māui (North Island) (Beresford et al 2018;Toome-Heller et al 2020).…”