Spruce’s genes determine the spread of the root rot

Heterobasidion-root rot causes major damage in coniferous forests across Europe and is one of the most economically costly forest diseases in Sweden. About twenty years ago, researchers at Skogforsk showed that different clones of spruce had different resistance to root rot caused by natural infections of the root rot fungus, Heterobasidion annosum s.l. Professor Malin Elfstrand says that this was an important breakthrough:

– However, it raised the questions: do more resistant spruces all react and protect themselves in the same way and whether resistance differs depending on which genotype of H. annosum that is attacking the tree? 

Genetic variation is the most important factor

In a study recently published by Hernán Capador-Barreto and his colleagues in BMC Plant Biology, the researchers wanted to try to answer just those questions. They used ten of the most resistant spruce clones from the previous study that were inoculated with four genetically different individuals of H. annosum s.l. 

– The results showed that variation in the spruce's resistance is the most important factor behind how much the fungus spreads and damages the spruce– not the interaction between specific spruce and fungus combinations. It was primarily the spruce's own genes that determined how far the disease spread, says Hernán Capador-Barreto.

By analyzing the gene activity in both the spruce bark and H. annosum, the researchers were able to see that different spruce clones reacted in different ways when infected, even though they appeared to be equally resistant to H. annosum. The gene expression patterns also differed to some extent depending on which fungal genotype the spruce interacted with.

A swift response gives the spruce the upper hand against the fungus

The gene activity of the less resistant spruces showed small changes at the beginning of the infection and very large changes in gene expression later during the infection. While the more resistant trees changed gene expression of key genes early during the infection. 

– A particularly interesting discovery was that genes encoding receptors – proteins that recognize attacking organisms and activate defenses – were strongly activated in the most resistant spruce clone early during the interaction. At the same time, such genes were less active in the most sensitive clone. The study therefore shows that the course of the infection is determined early in the interaction and that different spruce genotypes can use different defense strategies to achieve similar levels of resistance, says Malin Elfstrand.

Link to the study: https://doi.org/10.1186/s12870-025-07438-1