Ingestion of infected roots by feral pigs provides a minor vector pathway for kauri dieback disease Phytophthora agathidicida

Identifying vectors of soil-borne forest pathogens is crucial in limiting disease spread. Phytophthora agathidicida causes kauri dieback disease, killing kauri (Agathis australis (D.Don) Lindl.), Aotearoa-New Zealand's largest endemic tree. Currently incurable, management focuses on spread prevention. Feral pigs (Sus scrofa) are implicated in spread, through ingestion of infected material; congeneric Phytophthora cinnamomi is known to survive pig gut passage. We investigated P. agathidicida survival of pig gut passage in a captive feeding experiment, and assessed P. agathidicida incidence in feral pig stomachs from DNA. We detected viable P. agathidicida from a kauri root retrieved from captive-fed pig faeces, providing proof of concept that pigs can internally vector P. agathidicida. However, we detected only one positive, despite processing a total of 11.2 m of passaged roots and 800 millet (Pennisetum glaucum (L.) R.Br.) seeds, from 12 pigs. We did not detect P. agathidicida in any of 184 wild-caught feral pig stomachs, but did detect five other Phytophthora species including P. multivora and P. cinnamomi. Ingestion of contaminated material by feral pigs is probably a minor pathway for P. agathidicida, and a higher risk pathway for P. cinnamomi. We highlight the need to test Phytophthora species individually, as pathways of spread may be considerably different between related species.