Inoculating potted Japanese knotweed plants with the pathogen for the experimental field trial

Infection with M. polygoni-cuspidati under greenhouse conditions

Natural field infection of Japanese knotweed with M. polygoni-cuspidati in Japan

Natural field infection of Japanese knotweed with M. polygoni-cuspidati in Japan

Fungal mycelium of M. polygoni-cuspidati in liquid culture

Natural field infection of Japanese knotweed with M. polygoni-cuspidati in Japan

Experimental field trial with Mycosphaerella polygoni-cuspidati set up in the grounds of CABI UK

Experimental field trial with Mycosphaerella polygoni-cuspidati set up in the grounds of CABI UK

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Project Overview

So, what’s the problem

Japanese knotweed (Fallopia japonica) is a highly invasive species in the UK, mainland Europe, North America and parts of Oceania.

Introduced from Japan in the mid-19^th century as a prized ornamental, the plant species soon became problematic in its entire exotic range exerting detrimental impacts on both biodiversity and local infrastructures.

Due to its ability to form dense monocultures and to regrow from tiny fragments of rhizome, Japanese knotweed is often governed by special legislation in individual countries, like in the UK where it is illegal to cause it to grow in the wild (Wildlife and Countryside Act 1981).

Currently, the weed can be partially controlled using chemicals however, this is costly and considered unsustainable due to the ease of spread of the invasive, and the increasing restrictions on using herbicides in many countries.

Classical biological control programmes targeting Japanese knotweed were initiated in the UK and the USA in 2000, shortly followed by Canada in 2007. From the suite of natural enemies associated with Japanese knotweed in its centre of origin, the psyllid, Aphalara itadori, and the fungal leaf-spot pathogen, Mycosphaerella polygoni-cuspidati, were selected as having the highest potential as biocontrol agents. The psyllid has already been released as a classical agent in the UK, USA and the Netherlands, whilst the leaf-spot pathogen has been undergoing evaluation as a potential mycoherbicide agent.

What is this project doing?

The fungal leaf-spot, Mycosphaerella polygoni-cuspidati, is a damaging pathogen of F. japonica which is common and widespread on its host in the native range.

A thorough evaluation showed that the pathogen is not suitable as a classical biocontrol agent for Japanese knotweed as it can cause restricted disease symptoms on a couple of UK and North American non-target plant species under quarantine greenhouse conditions. However, the pathogen is thought to hold promise as a mycoherbicide due to its genetic and biological properties.

Such a potential mycoherbicide would be based on an isolate of only one mating type out of the two complementary types required by the pathogen for reproduction, persistence and spread in the field. This would allow targeted application while minimizing the risk to non-target species.

To protect this idea, international patent applications held in the name of the Secretary of State for Environment, Food and Rural Affairs, UK (DEFRA) have been filed and published, and a European patent has already been granted.

Building on previous work, the aim of this project is to undertake “proof of concept” research into the potential mycoherbicide in collaboration with the private sector to assess the scope for, and, hopefully, ultimately develop a product which could be applied in much the same way as a herbicide.