| Replant disease is a serious problem for the sustainable production of strawberry. So far, the research on the cause about the increasing replant disease year by year is staying in the single factors, such as the increase of the soil-borne diseases, the allelopathy and the deterioration of soil physical and chemical properties, and so on. This study proved firstly that the interaction existed between the allelochemical 4-Hydroxybenzoic acid and Fusarium oxysporum Schl.f.sp. fragariae. The quickening-supporting effect of the allelochemical 4-Hydroxybenzoic acid in the root exudation or decomposed liquid was proved by testing the photosynthesis, the growth of strawberry and the disease index. Based on the result, the feasibility was discussed by screening the PA degradation strain to weaken the inhibitory effects of 4-Hydroxybenzoic acid and F. oxysporum on the growth of strawberry, and the solution for reducing or eliminating the strawberry replanting diseases was provided. The main results were as followed:Compared with the single treatment with 4-Hydroxybenzoic acid and F. oxysporum, the treatment of 4-Hydroxybenzoic acid in combination with the pathogen caused the bigger inhibitory. The combination treatment significantly reduced the indicators of photosynthesis contents of leaves, such as Pn and Ci; improved the original fluorescence and reduced the maximum amount of photosynthetic electron transfer, and finally resulted in the growth of biomass. On the other hand, the amount of F. oxysporum in the cultivation and the disease index were becoming higher and higher. As a result, the infection rate and the disease index were increased as 4-Hydroxybenzoic acid was applied.At the same time, the contents of Serine and Threonine in the exudates were increased, which can promote the growth of F. oxysporum, but the content of Aspartate was reduced, which inhibited the growth of F. oxysporum. There was a evidence that the allelochemical enhanced the disease of the strawberry root and promoted occurrence of the replant disease to happen.The protection enzyme activity of the strawberry roots and the anti-oxidation system were changed when the strawberry treated by 4-Hydroxybenzoic acid and F. oxysporum. the lipid per oxidation was speeded up; H~+-ATPase activity of roots also was reduced significantly, the cell membrane was hurt and the nutrient water leakage were led to. In the end, the growth of strawberry plants hampered and the roots disease index rose.B3512, with a high-efficiency degradation to PA, was isolated from the soil through the selective medium at the condition with PA (2000 ug/mL) as the only carbon source. B3512 was identified as Acinetobacter according to the shape, physiological and biochemical characteristics of the strain. Then, the best conditions were 28℃, pH7, nitrogen 600 ug/mL, carbon 2000 ug/mL and 120 rpm. With the conditions, the rate of degradation could reach by the 95.7% in the 48 hours. At the same time, the strain B3512 also can degradate the benzoic acid, which is another allelochemical.The root activity was improved and the root cell membrane permeability was reduced significantly after inoculated with the degradation strain B3512 The degradation strain B3512 enhanced the growth of the roots, the area per plant, the height of plant and the fresh or dry weight and so on. It mitigated effectively the 4-Hydroxybenzoic acid bad effects on the growth.The rhizosphere microecological environment, caused by the continuous cropping strawberry, is conductive in increasing the number of pathogen groups, reducing the root resistance, and the allelochemical promotes the changes in some direction.
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