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Fungal root diseases

Plants are most susceptible to fungal root diseases during germination and growth of the seedlings. Both coniferous and deciduous species are affected during production of transplants in tree nurseries.

Damping-off is the most common disease in forest nurseries causing one third of the losses due to diseases in nurseries. Often, seedlings are completely lost. A complex of various fungal pathogens can be involved in damping-off; Fusarium spp., Phytophthora spp., Rhizoctonia spp. and Pythium spp. are considered to be the major cause of damping-off in forest nurseries.

What are the symptoms of fungal root diseases?

Damping-off fungi cause disintegration of stem and root tissues, wilting and collapsing and seedling death.

What are the economic consequences of fungal root diseases?

Damping-off is the most important cause of losses during transplant production. The disease may cause disruption in the continuity of nursery production and losses must be supplemented by purchasing suitable material from an external source. As much manual work is involved in the production of seedlings the economic importance is high.

How can these diseases be controlled?

Preventive treatments include measures of good agricultural practice. Use of high quality seeds can reduce problems as well as avoiding the use of contaminated soil and irrigation water. Soil with higher pH can also contribute to prevent damping-off. Currently, chemical fungicides are registered and used for seedling protection against fungal diseases in forest nurseries. The development of biological methods to protect seedlings and their implementation in nurseries will be an alternative component of an integrated pest management strategy in forest nurseries.

Use of pesticides

A prolonged process of obtaining authorization and certification to use specific chemical pesticides, including fungicides, in forestry is needed, especially in FSC certified forests (info.fsc.org).  The amount of chemical treatments to be used against damping-off during the growing season is also restricted. There is a considerable environmental impact of pesticides: negative side-effects on non-target species, danger to users/animals/native species, accumulation in the environment, and drift from the original point of application.
Less restrictions are expected when environment-friendly BCAs will be used.

BIOCOMES biological control agent

Biological control agents based on microbial antagonists will be tested. Bacterial or fungal antagonists can provide several beneficial effects against damping-off diseases. The microbials can have direct effects on the pathogenic complex reducing their growth and preventing establishment in the rhizosphere. Fungal antagonists like Trichoderma spp. can even parasitize plant pathogenic fungal mycelium. Most of the biological agents promote growth of the young plants which reach a non-susceptible developmental stage earlier than non-treated transplants. A so-called disease-escape effect is the consequence of using growth-promoting micro-organisms.

Biological control agents can be used to treat seeds of forest plants. After germination the microorganisms establish themselves in the rhizosphere (rhizosphere-competence) and compete with pathogens for space and nutrients thus preventing the establishment of damping-off fungi. Another beneficial effect of biological control agents is their potential to induce systemic resistance in the forest plants making them more resistant to pathogen attack. The use of biological control agents is more target-specific and hence has fewer negative effects on non-target organisms or even beneficial organisms in the rhizosphere. Biological control agents with rhizosphere competence are self-sustaining, growing with the plant roots, and can provide long-term protection.
With further restrictions on chemical fungicides forestry managers lack effective preparations against soil-borne fungal pathogens causing root diseases. Currently,  only one biological control agent is registered for control of damping-off in Poland. Many fungicides are registered for other crops but not for forest plants as the market is often not justifying high registration costs, resulting in restricted access to fungicides against root infection in forest nurseries. This means that there is a strong need for biological control agents as alternatives for damping-off control in forest nurseries.

Photo: Quercus robur.
Seedlings infected with damping-off fungi (Fusarium sp., Rhizoctonia sp., Pythium sp. and Phytophthora sp.). Infected plants have slightly sunken brown lesions on the stem at or below the soil line. The rotted roots are brown or black and water-soaked. The outer portion of the root can easily be separated from the inner core. Foliage of infected plants is discoloured and falls prematurely starting with the oldest leaves. Picture: IBL.

Katarzyna Sikora
Katarzyna Sikora
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Biological Control Agents

At the end of the project several biological control agents will have been successfully used in agricultural applications. The project will test whether we find comparable successful control of damping-off also in forestry plants.

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Current stage of the Biological Control Agent

75%

Month 36: Results of greenhouse trials for at least 3 BCAs against important diseases of at least 3 tree species, and recommendations for inoculation methods
Month 48: Report on efficacy of BCAs for disease suppression in forest nurseries

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