Composition Identification and Allelopathic Effect of Root Exudates of Ginseng in Different Continuous Cropping Years
In order to explore the mechanism of ginseng continuous cropping obstacle, the root exudates of ginseng plants for 3, 5 and 7 years were collected under indoor greenhouse cultivation conditions, and the main components of root exudates were identified by GC-MS, and the biological effects of root exudates were verified by biological detection. The results showed that the main substances identified by N3-N7 were acids, alcohols, esters, amines and pyrimidines, but the quantities and contents of these substances were different. The relative contents of p-hydroxybenzoic acid in N3-N7 were 0.78%, 1.15% and 2.82%, respectively. The concentrations of p-hydroxybenzoic acid in N3-N7 were 1.07 mg L-1, 1.96 mg L-1 and 4.05 mg L-1, respectively. Ginseng root exudates significantly inhibited the growth of ginseng seedlings, and the inhibition increased with the prolongation of continuous cropping years. The inhibition of p-hydroxybenzoic acid on ginseng growth showed obvious allelopathic effect, which increased with the increase of concentration. Root exudates of ginseng significantly promoted the growth of mycelia of ginseng rust rot fungi. The diameter of colony was the highest in N5 and the comprehensive allelopathic effect index was the strongest. With the increase of p-hydroxybenzoic acid concentration, the comprehensive allelopathy index increased first and then decreased. The colony diameter of 20 mg L-1 p-hydroxybenzoic acid concentration was the largest. It is concluded that with the prolongation of continuous cropping years of ginseng, the toxicity of root exudates is stronger; the promotion of ginseng root exudates on ginseng rust fungi aggravates the barrier of ginseng continuous cropping, and p-hydroxybenzoic acid is an allelopathic autotoxic substance secreted by ginseng root.