Identification and autotoxicity of root exudates of continuous cropping potato at different growth stages

Potato root exudates were collected from two treatments (CK: potato rotation with other crops; CP5: continuous potato cropping for five years) under field conditions to explore the possible obstacle mechanisms of continuous cropping of potato. The root exudates were collected at three growth stages - seedling, squaring and florescence stages. The chemical composition of the root exudates were determined by the GC-MS method and the autotoxicity of the exudates to potato plants tested in a pot experiment. The results showed that the main components of potato root exudates in both CK and CP5 treatments included glucides, organic acids, amines, alcohols, esters and pyrimidines, with glucides and organic acids as the dominant components. Also while the chemical composition of root exudates of CP5 was much more complex than that of CK, the content of organic acids in CP5 was significantly higher than in CK. The compound, dibutyl phthalate (DP), existed only in root exudates of CP5, with relative contents of 0.16%, 0.21% and 0.24% respectively at seedling, squaring and florescence stages. Root exudates of CP5 also was tested positive for the compound palmitic acid (PA), with relative contents of 0.34%, 1.12% and 0.47% respectively at seedling, squaring and florescence stages. Although PA was detected in CK treatment, it only appeared at squaring and florescence stages in respective concentration of 0.56% and 0.24%. Biological analyses showed that PA and DP significantly inhibited potato growth. The inhibiting effect of PA or DP of 1 mmol·L^-1 was far exceeded that of 0.5 mmol·L^-1 concentration. Continuous potato cropping changed the composition of potato root exudates, and PA and DP were autotoxins of potato root exudates, though with no superimposition effects. Potato root secreted much more root exudates at squaring stage, which period was suitable for collection of potato root exudates.