Quasi-targeted metabolomics revealed isoliquiritigenin and lauric acid associated with resistance to tobacco black shank

Abstract

Tobacco black shank (TBS), caused by Phytophthora nicotianae, is a severe disease. Plant root exudates play a crucial role in mediating plant-pathogen interactions in the rhizosphere. However, the specific interaction between key secondary metabolites present in root exudates and the mechanisms of disease resistance remains poorly understood. This study conducted a comprehensive comparison via quasi-targeted metabolomic analysis on the root exudate metabolites from the tobacco cultivar Yunyan87 and K326, both before and after inoculation with P. nicotianae. The results showed that the root exudate metabolites changed after P. nicotianae inoculation, and the root exudate metabolites of different tobacco cultivar was significantly different. Furthermore, homovanillic acid, lauric acid, and isoliquiritigenin were identified as potential key compounds for TBS resistance based on their impact on the mycelium growth of the pathogens. The pot experiment showed that isoliquiritigenin reduced the incidence by 55.2%, while lauric acid reduced it by 45.8%. This suggests that isoliquiritigenin and lauric acid have potential applications in the management of TBS. In summary, this study revealed the possible resistance mechanisms of differential metabolites in resistance of commercial tobacco cultivar, and for the first time discovered the inhibitory effects of isoliquiritigenin and homovanillic acid on P. nictianae, and attempt to use plants secondary metabolites of for plant protection.

Keywords: Phytophthora nicotianae; Tobacco; isoliquiritigenin; lauric acid; quasi-targeted metabolomics; root exudates.

Figure 1.

Resistance identification of Yunyan87 and K326 against TBS. (a) The incidence rate of Yunyan87 and K326 inoculated with P. nicotianae for 4 and 8 days. (b) TBS symptoms of tobacco plants 8 days with P. nicotianae (***, p < 0.001; ****, p < 0.0001; t test; the error bars represent the standard deviation of three repetitions).

Figure 2.

Effects of root exudates from Yunyan87 and K326 on the mycelial growth of P. nicotianae. (a) The colony diameter of P. nicotianae treated with root exudates of Yunyan87 and K326 for 4 days. (b) Mycelial growth of P. nicotianae after 4 days treatment with root exudates of Yunyan87 and K326. Yi and Y represent root extract from pathogen inoculation and non-inoculation of Yunyan87, respectively; Ki and K represent root extract from pathogen inoculation and non-inoculation of K326, respectively; different lowercase letters marked on the column indicate significant differences between groups at p < 0.05; the error bars represent the standard deviation of three repetitions.

Figure 3.

Principal component analysis (a) and hierarchical clustering analysis (b) of metabolites of different tobacco cultivar non-inoculation and inoculation. Yi and Y represent root extract from pathogen inoculation and non-inoculation of Yunyan87, respectively; Ki and K represent root extract from pathogen inoculation and non-inoculation of K326, respectively.

Figure 4.

The numbers of differential compounds before and after inoculation of P. nicotianae in both tobacco cultivars. (a) Histogram. (b) Venn diagram. Yi and Y represent root extract from pathogen inoculation and non-inoculation of Yunyan87, respectively; Ki and K represent root extract from pathogen inoculation and non-inoculation of K326, respectively.

Figure 5.

Mycelial growth of P. nicotianae after 4 days treatment with isoliquiritigenin, homovanillic acid and lauric acid with strong inhibitory activity.

Figure 6.

Pot control effect of isoliquiritigenin, lauric acid and oxadixyl·mancozeb against TBS. (a) The TBS incidence of Yunyan87 inoculated with P. nicotianae for 4 and 11 days after treatment with two compounds and oxadixyl·mancozeb. (b) TBS symptoms in tobacco plants 11 days post-inoculation with P. nicotianae after treatment with three compounds and oxadixyl·mancozeb. Different lowercase letters marked on the column indicate significant differences between groups at p < 0.05; the error bars represent the standard deviation of three repetitions.