Effect of continuous cropping on allelopathy of peanut root exudates

Root exudates of peanut at podding stage under 3 years and 5 years of continuous cropping, and rotation cropping were collected using the continuous collection method. Allelopathic effects of the collected root exudates on soil microbes, peanut seed germination, seedling growth and development and membrane peroxidation were analyzed. The effects of continuous cropping on allelopathic effectiveness of peanut root exudates were also investigated. Results showed that root exudates at peanut podding stage stimulated the growth of root rot fungi (Fusarium sp.) 36194 mycelium, and activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and the content of malondialdehyde (MDA) in peanut leaf. It, however, inhibited the growth of N-fixing bacteria (Bradyrhizobium vigna) 14046, the elongation of seedling radicle and height, the fresh weights of leaf and stem, and root, and leaf chlorophyll content. The stimulating and inhibitive effects of peanut root exudates increased with both the increasing concentration of exudates and the length of period of continuous cropping. Accumulation of allelopathic substances in root exudates at podding stage was a possible obstacle to continuous peanut cropping.