Importing the rust fungus Uromyces pencanus as a biocontrol agent for Chilean needle grass, Nassella neesiana, into New Zealand – a decade long journey

Abstract

Chilean needle grass [CNG] (Nassella neesiana (Trin. & Rupr.) Barkworth), mostly a pasture weed in New Zealand, outcompetes and displaces pasture species, and can cause major damage to stock. Native to Argentina, CNG is widespread in the New Zealand regions of Hawke’s Bay and Marlborough, with smaller sites in northern Canterbury and Auckland. In 1998, a biocontrol programme for CNG was initiated in Argentina by Australia, followed by New Zealand. A rust fungus, Uromyces pencanus (Dietel & Neger) Arthur & Holw., was identified as the most suitable biocontrol candidate, with strain UP27 shown to be highly host specific. In 2011, the New Zealand Environmental Protection Authority (EPA) granted a five-year permission to import Uromyces pencanus. However, it took over a decade before permission to export the rust fungus from Argentina was finally approved. The holdup was caused by a document called the Convention for Biological Diversity and the Nagoya Protocol, a supplementary agreement to it. By the time a new EPA application was submitted in 2017, further host range testing of Austrostipa species native to Australia resulted in the unexpected production of U. pencanus spores on two non-target Austrostipa species: A. compressa (R.Br.) S.W.L. Jacobs & J. Everett and A. macalpinei (Reader) S.W.L. Jacobs & J. Everett. While neither of these Austrostipa species grow in New Zealand, testing of native Stipoid grasses was recommended. Only three native grasses belonging to the same Stipeae tribe as Nassella are present in New Zealand:Austrostipa stipoides (Hook.f.) S.W.L. Jacobs & J. Everett, Achnatherum petriei (Buchanan) S.W.L. Jacobs & J. Everett and Anemanthele lessoniana (Steud.) Veldkamp. Permission to export the rust fungus out of Argentina was finally granted in September 2021 during the Covid-19 pandemic. Due to a restricted number of flights worldwide, the culture took over three weeks to arrive and was no longer viable. In December 2022, a fresh culture was hand-carried from Argentina to New Zealand and has resulted in the successful establishment of U. pencanus on New Zealand CNG plants. The CNG rust fungus is the first plant pathogen exported from Argentina for biocontrol. The journey from finding a suitable biological control agent for CNG to getting a culture established in New Zealand is discussed.