Insights on the Structural and Metabolic Resistance of Potato (Solanum tuberosum) Cultivars to Tuber Black Dot (Colletotrichum coccodes)

Josep Massana-Codina; Sylvain Schnee; Pierre-Marie Allard; Adriano Rutz; Julien Boccard; Emilie Michellod; Marilyn Cléroux; Stéphanie Schürch; Katia Gindro; Jean-Luc Wolfender

doi:10.3389/fpls.2020.01287

Insights on the Structural and Metabolic Resistance of Potato (Solanum tuberosum) Cultivars to Tuber Black Dot (Colletotrichum coccodes)

Front Plant Sci. 2020 Aug 20:11:1287. doi: 10.3389/fpls.2020.01287. eCollection 2020.

Authors

Josep Massana-Codina^{1

2

3}, Sylvain Schnee¹, Pierre-Marie Allard^{2

3}, Adriano Rutz^{2

3}, Julien Boccard^{2

3}, Emilie Michellod¹, Marilyn Cléroux⁴, Stéphanie Schürch¹, Katia Gindro¹, Jean-Luc Wolfender^{2

3}

Affiliations

¹ Plant Protection Research Division, Agroscope, Nyon, Switzerland.
² School of Pharmaceutical Sciences, University of Geneva, Geneva, Switzerland.
³ Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, Geneva, Switzerland.
⁴ Changins College for Viticulture and Enology, University Western Switzerland, Nyon, Switzerland.

Abstract

Black dot is a blemish disease of potato tubers caused by the phytopathogenic fungus Colletotrichum coccodes. Qualitative resistance (monogenic) that leads to the hypersensitive response has not been reported against black dot, but commercial potato cultivars show different susceptibility levels to the disease, indicating that quantitative resistance (polygenic) mechanisms against this pathogen exist. Cytological studies are essential to decipher pathogen colonization of the plant tissue, and untargeted metabolomics has been shown effective in highlighting resistance-related metabolites in quantitative resistance. In this study, we used five commercial potato cultivars with different susceptibility levels to black dot, and studied the structural and biochemical aspects that correlate with resistance to black dot using cytological and untargeted metabolomics methods. The cytological approach using semithin sections of potato tuber periderm revealed that C. coccodes colonizes the tuber periderm, but does not penetrate in cortical cells. Furthermore, skin thickness did not correlate with disease susceptibility, indicating that other factors influence quantitative resistance to black dot. Furthermore, suberin amounts did not correlate with black dot severity, and suberin composition was similar between the five potato cultivars studied. On the other hand, the untargeted metabolomics approach allowed highlighting biomarkers of infection, as well as constitutive and induced resistance-related metabolites. Hydroxycinnamic acids, hydroxycinnamic acid amides and steroidal saponins were found to be biomarkers of resistance under control conditions, while hydroxycoumarins were found to be specifically induced in the resistant cultivars. Notably, some of these biomarkers showed antifungal activity in vitro against C. coccodes. Altogether, our results show that quantitative resistance of potatoes to black dot involves structural and biochemical mechanisms, including the production of specialized metabolites with antifungal properties.

Keywords: Solanum tuberosum; black dot (Colletotrichum coccodes); hydroxycinnamic acid amide; metabolomics; phellem; quantitative resistance; steroid derivative.