Dangerous as... mistletoe
Common mistletoe, which most of us associate with Christmas, is in fact a semi-parasitic plant that in recent years has been spreading rapidly in Europe and increasingly threatening silviculture. Some researchers list around 450 plant species as hosts for mistletoe. It causes massive damage to forests, orchards and plantations of crops. Until recently, mistletoe was mainly observed on deciduous trees such as poplars and lindens; however, in recent years a serious expansion of this parasite has also been observed on coniferous trees, i.e. pines and firs
– explains Dr Małgorzata Ruszkiewicz-Michalska from the Department of Algology and Mycology.
Foresters are sounding the alarm, especially as pine is the main tree grown in our country. Scientists suspect that the expansion of mistletoe into coniferous trees is related to climate change.
The development of mistletoe on pine trees leads to their death, as the parasite not only draws water and mineral salts from the host tree, but also facilitates access for other pathogenic organisms, as well as bark beetles. At the same time, mistletoe removal is very difficult. In the world, mechanical removal methods and chemical agents are used to combat it but unfortunately, they are only partially effective
– explains mgr Sebastian Piskorski from the Department of Algology and Mycology.
Fungi for rescue
In many countries biological methods of pathogen control using parasites have been recognised as beneficial and environmentally safe. To date, more than a dozen species of microscopic fungi have been identified that parasitise mistletoe. However, none of these have been sufficiently tested and used to develop a biological control agent for this semi-parasite.
In the spring of last year, researchers from the Faculty of Biology and Environmental Protection at the University of Lodz and the Institute of Forest Sciences at the Białystok University of Technology started a research project entitled "Grzyby ograniczające wzrost jemioły pospolitej" [Fungi limiting the growth of common mistletoe]. – This is the first stage of the project that involvs the search for fungal species that will be pathogenic to mistletoe and thus, limit its growth and spread – explains Dr Ruszkiewicz-Michalska. We collect mistletoe plants from all over the country and check for disease symptoms. If they are caused by fungi, we grow them on artificial media under laboratory conditions in order to subject them to a microscopic analysis and genetic studies – adds mgr Sebastian Piskorski, who is involved in the project.
A whole new species
In the course of the research, the scientists succeeded in discovering and describing a new species of the microscopic fungus Septoria krystynae Ruszk.-Mich., Janik-Superson, Piskorski & Wolkowycki. This fungus, found by Marek Wołkowycki (Institute of Forest Sciences of Bialystok University of Technology) in the Białowieża Forest, is a parasite of the common mistletoe and causes a disease called septoria leaf spot. – Whether the newly described species can be effective in controlling mistletoe in Polish forests depends on a number of factors – emphasises Dr Ruszkiewicz-Michalska. – Firstly, the pathogenicity conditions of this fungus and its effectiveness using different application methods should be investigated.
More effective than spraying?
– It is important to remember that fungus is not a chemical that you apply and get 100 per cent effectiveness. Fungi are living organisms that can mutate and adapt to new conditions – emphasises Dr Ruszkiewicz-Michalska. – Relatively recently, scientists have discovered that fungi can 'borrow' gene fragments from other organisms (bacteria, plants, animals and other fungi) and build them into their own DNA. This phenomenon is called horizontal gene transfer. This ability allows fungi to adapt more easily to the physiology of these organisms and parasitise them more effectively. However, it is easy to imagine that this ability can also be dangerous. Detailed research is therefore required before fungi can be used for parasite control.
– So far, Turkish scientists have identified two ubiquitous, polyphagous fungal species – Alternaria alternata and Acremonium kiliense – as effective mistletoe pathogens in laboratory studies – says mgr Sebastian Piskorski. When mistletoe was sprayed (the most practical method in the environment) with these fungal species, the plants demonstrated strong disease symptoms. Unfortunately, in order for a biological method of semi-parasite control to be effective, the used pathogens must be specific, i.e. they must have a narrow host range. Only then will the mycopreparation be safe for other plants and other organisms.
The next stage of the research
As part of their research, scientists from the University of Lodz and Białystok University of Technology plan to learn about the entire mycobiota of the common mistletoe that develops on trees in Polish forests. Thanks to the comprehensive results of these observations, it will be possible to test the pathogenicity of different fungal species against mistletoe.
Source: Faculty of Biology and Environmental Protection, University of Lodz
Text: Justyna Kowalewska (3PR Consulting)
Photos: dr hab. Małgorzata Ruszkiewicz-Michalska, Marek Wołkowycki