Identification of autotoxic compounds from Atractylodes macrocephala Koidz and preliminary investigations of their influences on immune system

Atractylodes macrocephala Koidz (A. macrocephala) is a traditional Chinese medicine that has been widely used in China, Japan, and Korea due to its health benefits. Autotoxicity, as one of the major problems hindering continuous cultivation of A. macrocephala, has been reported to inhibit plant growth by various means. However, the impact of autotoxicity on the plant immune system is rarely reported. In this study, 2, 4-Ditertbutyl phenol (2,4-DP), an autotoxic compound, isolated from root exudates and rhizosphere soil of A. macrocephala was identified by gas chromatography-mass spectrometry (GC-MS). The results of germination trials showed that 2,4-DP had a significant inhibitory effect on seed germination. In addition, in non-inoculated seedlings, three concentrations of 2,4-DP (0.1, 1 and 10 mmol/L) affected indicators of systemic acquired resistance (SAR): accumulation of salicylic acid (SA), activities of protective enzymes, atractylenolides contents, and increased the disease index (DI). In inoculated seedlings, 2,4-DP decreased indicators of SAR and increased the DIs at low and high concentrations but increased indicators of SAR and decreased the DI at a moderate concentration. These results suggest that 2,4-DP has an inhibitory effect on the plant immune system, but it can induce the SAR at a certain concentration by controlling the pathogenic fungi.