Table_3_Insights on the Structural and Metabolic Resistance of Potato (Solanum tuberosum) Cultivars to Tuber Black Dot (Colletotrichum coccodes).docx

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.

黑点病是马铃薯块茎上由病原真菌 Colletotrichum coccodes 引起的病害。关于黑点病，尚未报道存在单基因抗性（定性抗性）导致的过敏性反应，但商业马铃薯品种对该病的易感性存在差异，表明存在针对该病原体的数量性状抗性（多基因）机制。细胞学研究表明，解析病原体在植物组织中的定殖过程至关重要，而未经靶向的代谢组学已被证明在突出数量性状抗性相关的代谢物方面是有效的。在本研究中，我们使用了五种对黑点病易感性不同的商业马铃薯品种，并利用细胞学和未经靶向的代谢组学方法，研究了与黑点病抗性相关的结构和生化方面。使用马铃薯块茎皮层半薄切片进行的细胞学方法揭示了 Colletotrichum coccodes 定殖于块茎皮层，但并未穿透皮质细胞。此外，皮层厚度与病害易感性无关，表明其他因素影响对黑点病的数量性状抗性。进一步地，蜡质含量与黑点病的严重程度无关，且所研究的五种马铃薯品种的蜡质成分相似。另一方面，未经靶向的代谢组学方法允许突出感染生物标志物，以及组成型和诱导型抗性相关代谢物。在控制条件下，羟基肉桂酸、羟基肉桂酰胺和甾体皂苷被发现是抗性生物标志物，而羟基香豆素在抗性品种中被特异性诱导。值得注意的是，其中一些生物标志物在体外对 Colletotrichum coccodes 显示出抗真菌活性。总之，我们的结果表明，马铃薯对黑点病的数量性状抗性涉及结构和生化机制，包括具有抗真菌特性的特殊代谢物的产生。