Crops have a high nutritional value, which makes them essential to people. However, this also makes them attractive to harmful microorganisms, such as bacteria or fungi. In fact, most pathogens can only attack specific plants and there has been extensive research to try to discover how fungi locate their host plants. Until now, it was thought that host plants stimulate fungal spores in soil to germinate by releasing specific sugars, amino acids and other compounds from their roots - known as -root exudates- - thereby unwittingly triggering their own infestation. Researchers at the University of Göttingen have now shown that this is not the primary mechanism for triggering spore germination that leads to root infection. Instead, the activity of the spores is influenced by a combination of different abiotic factors and particular soil bacteria communities. The results were published in PLOS Pathogens.
The researchers found that sterile root exudates did not stimulate clubroot spores to germinate, and there was no difference between host and non-host plants. Experiments in the laboratory showed that the presence of soil bacteria as well as nitrate and certain sugars and amino acids is essential for triggering germination. The composition of the bacterial microbiome changed when nitrate and a suitable carbon source were available at a certain soil moisture: at this point, the proportion of stimulating bacterial groups increased and this triggered spore germination. It is still unclear which bacterial groups are required and the exact mechanism which ultimately breaks spore dormancy.
Original publication: Wang, Y.; Zheng, X.; Sarenqimuge, S.; von Tiedemann, A. The soil bacterial community regulates germination of Plasmodiophora brassicae resting spores rather than root exudates. PLoS Pathogens 19(3) 2023. DOI: 10.1371/journal.ppat.1011175 .
