White-baiting is a common pastime in Canterbury waterways. Fishing for the small delicacy requires a fine meshed net and a lot of patience. Lincoln University MSc student, Ashika Prasad, is fishing for even smaller creatures, fungal-like microorganisms called Phytophthora that, like whitebait, swim in our waterways. 

Phytophthora are notorious plant pathogens and, although small, can be devastating to New Zealand’s introduced and native plants. The kauri dieback pathogen, P. agathidicia, is a major threat to our iconic kauri trees and associated kauri forest ecosystems. Overseas there are increasing reports of the devastating impacts that exotic Phytophthora species, such as P. cinnamomi, P. kernoviae and P. ramorum, inflict on native ecosystems in Australia, Europe and North America. These pathogens also cause enormous economic losses on agricultural crops by causing agents of collar rot of apple, avocado root rot and late blight of potatoes (responsible for the Irish potato famine). 

Unlike true fungi, Phytophthora species produce motile spores, called zoospores, and are dependent on water for a significant part of their lifecycle, including their dispersal. Waterways, including rivers and streams, act as a potential pathway for invasion by these pathogens into new ecosystems. Along with colleagues at Manaaki Whenua – Landcare Research and funded by the Brian Mason Scientific and Technical Trust, Ashika is investigating the diversity of Phytophthora species in Canterbury waterways. 

Nets containing Phytophthora ‘food’, rhododendron leaves, cedar and pine needles, have been placed in waterways to attract the Phytophthora swimming spores. Disease lesions which developed on the plant leaves/needles, as a result of infection by the swimming spores, were isolated and allowed to grow to identify the type of Phytophthora present.

A large number of Phytophthora species were recovered, belonging to eight Phytophthora species and numerous Phytophthora sp. hybrids. Phytophthora lactustris was the most commonly isolated species followed by P. gonapodyides with 62 isolates. All but one of the Phytophthora species recovered have been previously reported from New Zealand. Interestingly, over 50% of the isolates recovered were hybrids of two Phytophthora species, whilst the parent strains were either not recovered or only at low occurrence. 

Many of the Phytophthora species detected are pathogenic on tree species living by waterways. They are likely weak pathogens since, although ubiquitous in waterways, there is a lack of diseased plants or trees in these areas. However, this needs to be confirmed along qith just how infective the Phytophthora hybrids recovered are to New Zealand native and cultivated crop plants.

The study has demonstrated the potential risk of waterways to spread potential micro-organism pathogens into new areas. Something to ponder on your next white-baiting trip.

Article written by Associate Professor Eirian Jones who helped to supervise this research.