Allelopathic Effect Of Phenolics And Its Role On Apple Replant Disease Mechanism

Apple production is in a process of transition from area enlargement to stable area and high-quality fruits. Apple trees in most of China dominant production areas experiences a full fruit period and senescence phase. Owing to lack of soil resources, replant becomes a serious problem in fruit tree nursery and old orchards. Autotoxicity of phenolics is one of the most important factors contributed toward the occurrence of crop replant disorder. To explore the effect of phenolics on apple replant syndrome, experiments were conducted to investigate the growth of different kinds of apple rootstock seedlings and analyze their root exudates both in pots and natural conditions. Effect of root exudates on seedling's growth was measured. Effect of application of organic materials and crop rotation were determined to improve growth of apple seedling in replant soil. The results were as follows:1 Ten phenolics were separated successfully with Waters high performance liquid chromatography (HPLC), gradient pump with waters solvent organizer at 280nm, with the flow rate of 1ml/min. The separation column was AichromBond-1 (250mm×4.6mm i. d.).The gradients were mixed with actonitrile (solvent A) and water (adjustd to pH2.8 with acetic acid as solvent B). The composition of the gradients were: 0～30min, 5% A plus 95% B, 35～42min, 35%A plus 5% B, 42～45min, 5% A plus 95% B. This separation method was suitable for quantitation of phenolics in root exudates of fruit trees.2 Apple, cherry, jujube and peach seedlings showed different exudation abilities. The largely components of apple root exudates were phloroglucinol, phloridzin and phloretin, which were up to 80% total phenolics. Root exudates of peach were mainly benzoic acid and caffeic acid. The main phenolic in cherry root exudates was benzoic acid. Cinnamic acid and its derivatives were the major parts in jujube root exudates, no benzoic acid was detected. The content of phenolics in root exudates of apple and peach was 7 to 8 times than that of cherry and jujube.3 Phenolics contents were determined in root exudates of different types of apple rootstocks. The main component was phloroglucinol. The content of phenolics in root exudates of apple rootstocks was in the following order: huailaihaitang (Malus micromalus...