Molecular interactions between quinoa, the biocontrol agent Trichoderma and the pathogen Peronospora variabilis

Sammanfattning: Plants have developed complex molecular mechanisms to recognize and respond to the different microorganisms present in their surroundings. The most studied response mechanisms are plant defense responses. These defense response mechanisms share many similar components with the plant response mechanisms to beneficial microbes. Therefore, studying the defense response mechanisms against pathogens can contribute to the understanding of compatible and incompatible interactions with beneficial microbes.In this work, the molecular interactions of quinoa with the pathogen Peronospora variabilis, causal agent of the downy mildew disease, and the interactions of quinoa with the beneficial biocontrol fungi Trichoderma harzianum were studied. Experimental systems for interaction experiments were developed and used, followed by morphological, biochemical and transcriptomic analysis. We describe the response of two quinoa cultivars to the infection of P. variabilis under controlled conditions. The quinoa cultivar Kurmi was more tolerant to P. variabilis infection than the Real cultivar, despite the lack of hypersensitive response. The defense response observed in the Kurmi cultivar might be mediated by the jasmonic acid signaling pathway. Cultivars that can trigger hypersensitive response are more resistant to P. variabilis than Kurmi and therefore a better selection for agriculture.Quinoa in the presence of Trichoderma had variable outcomes depending on the growth conditions. We observed that quinoa growth was promoted in regular soil experiments or by interaction with Trichoderma volatile compounds in axenic co-culture. However, the growth of two quinoa cultivars was significantly inhibited by T. harzianum in axenic co-culture and in steamed soil experiments. The transcriptomic data of the quinoa growth inhibition by Trichoderma suggests activation of molecular signaling very similar to the signaling observed during defense response against pathogens. Further, we observed a specific group of quinoa plant defensins to be more rapidly induced by Trichoderma in a resistant cultivar but not in a susceptible one. These plant defensins showed a recent evolutionary expansion and could play a major role in providing pathogen resistance to certain quinoa cultivars.In order to protect quinoa from P. variabilis infections by Trichoderma application and enhance the quinoa yields in agricultural systems might be necessary to perform compatibility tests between the Trichoderma biocontrol agents and the quinoa cultivars. These compatibility tests should be performed in regular soil.