Potential for dissemination of Phytophthora cinnamomi by feral pigs via ingestion of infected plant material

Abstract

Feral pigs have long been implicated as potential vectors in the spread of the devastating plant pathogen Phytophthora cinnamomi due to their rooting and wallowing activities which may predispose them as vectors of infested soil. In this study, we aim to determine whether feral pigs have the potential to act as vectors of plant pathogens such as P. cinnamomi through their feeding activity. The typically omnivorous diet of feral pigs may also lead to the passage of P. cinnamomi infected plant material through their digestive system. This study investigates the potential for feral pigs to pass viable P. cinnamomi in their faeces following the ingestion of millet seeds, pine plugs and Banksia leptophilia roots inoculated with P. cinnamomi. Recovery rates of P. cinnamomi from the millet seeds, pine plugs and B. leptophilia roots following a single ingested bolus were 33.2, 94.9 and 10.4 %, respectively supported by quantitative PCR analysis. These results demonstrate that P. cinnamomi remain viable within infected plant material following passage through the pig digestive tract, although the digestive processes reduce the pathogen’s viability. An inverse relationship was observed between the viability of infected material and passage time, suggesting that partially digested plant material provides protection for P. cinnamomi against the adverse environmental conditions of the pig digestive tract. Phytophthora cinnamomi remained viable for up to 7 days in larger pieces of colonised woody plant material such as the pine plugs. A plant infection trial using passaged P. cinnamomi colonised pine plugs showed that even material that remained in the digestive tract for 7 days was capable of infecting and killing healthy plants, susceptible to P. cinnamomi. This study provides compelling evidence that feral pigs have the ability to transport viable P. cinnamomi in their digestive tract.