Friend or Foe? Biocontrol interactions of Pythium oligandrum within the potato cropping system

Abstract

The potato crop is a valuable but vulnerable food source on a global level. It is under constant pressure from destructive plant diseases such as early and late blight. Traditionally to control these diseases farmers have relied heavily on synthetic fungicide use. It is evident that the use of agrochemicals such as synthetic fungicides can cause unwanted effects on the environment, and human health. Thus, there is a need for a more sustainable approach to control diseases in the potato cropping system. One approach could be to use biological control agents, (BCAs) such as mycoparasitic Pythium species to control the disease. However, to utilize these BCAs in the best way we need to increase our fundamental knowledge about their biology and interactions within potato cropping systems. Therefore, the aim of this thesis is to broaden our fundamental knowledge of the mycoparasitic Pythium species, Pythium oligandrum and Pythium periplocum, and how they differentiate from their phytopathogenic counterparts. Further, the thesis also pinpoints characteristics that determine mycoparasitism in these two Pythiums, and how this relates to their biocontrol abilities, at the molecular level. This was elucidated using comparative genomics, transcriptomics. The result showed that ABC transporters, AVH-like RXLR effectors, and an expanded CAZyme among other things, are conserved and important for mycoparasitism, by P. oligandrum and P. periplocum both when preying on phytopathogens but also in comparison to closely related plant pathogens. This thesis also explores if P. oligandrum can be used as an antagonist against early blight disease on potato plants. The results showed that P. oligandrum did induce disease suppression in potato in controlled greenhouse environments, however in the field trials when the disease pressure was high the effects disappeared. The thesis also explores if and how P. oligandrum interacts with the potato plants. The results showed that P. oligandrum induced biostimulation in potato both in controlled environments and field studies, although the biostimulation was in a plant-genotype dependent manner. Finally, the thesis investigates the impact on the resident rhizosphere microbiome of field grown potato plants when P. oligandrum was applied. The results showed that P. oligandrum has a very limited impact on the diversity and community structure in the rhizosphere of potato. Overall, the work in this thesis has generated a deeper understanding of the fundamental biology of the mycoparasitic Pythium species and how they differ from plant pathogens. An increased understanding of the environmental consequences and how P. oligandrum can be utilized as a BCA in the potato cropping system has been elucidated. This work also contributes with pivotal knowledge about how P. oligandrum can be utilized in an IPM strategy in the potato agricultural cropping system.

Alternative strategies to treat potato early blight

“…The mode of action of these substances varies with the product but includes outcompeting the pathogen, infecting, feeding on or producing toxins to kill the pathogen. An alternative treatment, or "bioprotection", can also work as a plant resistance inducer (PRI) by activating plant innate immunity or producing plant hormones that further protect the plant from pathogen attack (Stenberg et al, 2021;Andersen, 2023). In Paper II, four different alternative substances were evaluated in greenhouse and field trials for their effects on the rate of disease.…”