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It is vital to manage pathogenic fungi in forest nurseries

Published: 06 May 2024
Greenhouses with pine seedlings in front. Photo.

Increased knowledge about pathogenic fungi in nurseries can improve the measures used to protect the tree seedlings. Therefore, in her doctoral thesis, Rebecca Larsson has studied the occurrence of pathogenic fungi on spruce, pine, and larch seeds; healthy pine needles, as well as fungal spores in the air around the nurseries.

Fungal diseases can result in economic losses in forest nurseries. In Sweden, primarily Scots pine and Norway spruce are densely cultivated in trays consisting of small pots and the same tree species is grown over a large area. The tree seedlings are taken care of mechanically with high-tech equipment.

Preventing fungal damages

These conditions can favour a rapid spread of disease-causing fungi among the tree seedlings. To prevent fungal infections, various methods are applied, such as keeping the equipment and greenhouses clean, removing infected plants, or reducing moisture around the seedlings. When an infection occurs and there is a risk of extensive damage, nurseries use chemicals to prevent the fungus from further spreading.

– To minimise the use of chemicals, the nurseries primarily work preventively. But these preventive practices could be improved if there were better knowledge about the disease-causing fungi occurring in nurseries. This could for example involve understanding when and where different species of fungi occur, says Rebecca.

Fungal communities in five nurseries were investigated

In her doctoral thesis, Rebecca has studied the occurrence of common fungi known to cause serious infections, as well as the presence of new potentially disease-causing fungi. Her research focused on studying fungal communities from commercial seeds of spruce, pine, and larch, healthy pine needles and finally from fungal spores dispersed in the air around the nurseries. A total of five nurseries were included in the studies.

– My results showed that seedborne fungal communities were distinguished between the seed surface and the seed tissue, where fungi from the seed surface showed a strong host-affinity and regional dependence. Moving seeds between different geographic regions could be a potential source of the spread and introduction of fungal species, says Rebecca.

The foliar and airborne fungal communities comprised high species richness and showed clear temporal shifts over the seedling growing seasons.

– I also tested biological treatments that can work against pathogenic fungi and stimulate plant growth, but they did not show any effect in my studies.

Common fungi and Diplodia sapinea was found

All fungal communities in the studies showed a high prevalence of nursery fungal pathogens, for example Cladosporium sp., Botrytis cinerea, Phoma herbarum, and Sydowia polyspora. Rebecca also found infections caused by the relatively unknown fungus Diplodia sapinea in pine seedlings. There was also some presence of D. sapinea on the seeds and from the airborne spores.

– My findings contribute to developing disease management strategies in forest nurseries. It is important to manage fungal pathogens to maintain healthy tree seedling production, concludes Rebecca.