The Mechanism Of Eggplant (Solanum Melongena L.) Replanting Problem

The effect of continuous mono-cropping of eggplant on seedling growth were studied in pot experiments. The 45-day-old seedlings height, leaf area, main root length and total root length of the eggplants under continuous mono-cropping decreased significantly than of no-replanting eggplants, which resulted in fresh weight reduction eggplants shoot and root. The main reason for the declined nutrients absorption was from bad root development.Meloidogyne affected the 19-day-old seedlings growth, and the adverse effect from Meloidogyne became more severe with the development of eggplants. Although Meloidogyne were eliminated by autoclaving in continuous mono-cropping soil, eggplant seedling growth was not improved anyhow compared to no-replanting ones growing in sterilized soil. And 7 days after sowing, the germination of eggplant seeds under continuous mono-cropping were lower by 15% than that of no-replanting ones, suggesting Meloidogyne and allelopathy might play some roles.The effect of eggplant residues were studied in continuous mono-cropping with pot experiments. The results showed that eggplant residues inhibited seedling growth obviously, and the water soluble substance from the residues inhibited radicle growth of eggplants, indicating that eggplant residues contained allelochemicals, and the main sources of allelochemicals were rain washing of shoot from above ground and residue decomposing from root. Allelopathic effects varied in plant tissues, leaf allelopathic effect was the strongest, stem took second place, and root was the weakest.Methanol soluble components in water extracts inhibited the growth of eggplant embryo, radicle and seedling soluble as same as the water extracts original solution. Thus the methanol dissolvable components contained some allelopathic substances toxic to eggplant. Root activity of eggplant seedling decreased with the concentration of the methanol isolatable components increasing. Autotoxic substances in the methanol isolatable fraction suppressed the absorption of NOf, PC^3", K+, Mg2+ and Ca2+, implying the inhibition effect of the substances on ion uptake was one of the important mechanisms in allelopathy.Root exudates collected by solution culture had strong allelopathic effects on the growth and development of eggplant radicle and embryo. The root exudates could be separated by extraction, and both the acidic and alkaline components had strong biological activity, indicating root exudate effect was one of the important sources of allelochemicals.Allelochemicals were isolated and identified in the extracted of eggplant residues, root exudates and continuously mono-cropping soil by column chromatography method, extraction method and GC-MS method. Many potential allelochemicals could be detected, including 1,2-Benzenedicarboxylic acid ramification; Phenol, 2,6-bis(l,1-dimethyIethul); Hexaedcanoic acid, methyl ester; Heptadecanoic acid, methyl ester etc.. Therefore, root exudates and the residues were the source of the allelochemicals in soil.Root exudates by sand culture stimulated Verticillium wilt spore germination and mycelium growth.Root exudates from different cultivars had distinctly promoting effects. Changqie 9318 had stronger effects, and Yuanza 2 had weaker effects. Determination of the amino acids in root exudates indicated that contents of amino acids were related to the promoting effects. The influence of amino acids on Verticillium wilt varied with amino acids and the main amino acids exudated by eggplant root promoted the growth of Verticillium wilt mycelium, and the amino acids in root exudates were one of the factors causing the disease.