The Effect Of Soil Ecological Environment On The Colonization Of Serratia Plymuthica A21-4

The power of rhizosphere colonization for the biocontrol bacteria is a critical factor to prevent soil-borne plant diseases biologically, which affected by many factors. The analysis of this paper focus on the effects of ecological environment, such as the physical, chemical and micro-ecological environment, upon the biocontrol bacteria Serratia plymuthica A21-4 (S. plymuthica A21-4) in the rhizosphere colonization of pepper and cucumber plants in soil. The effects of ecological environment have been primarily detected, which laid the groundwork of enhancing and stabilizing the effect of biocontrol.In physical environment, colonization of S. plymuthica A21-4 in the rhizosphere soil and plant roots is significantly affected by different qualities of soil. It is favour the rhizosphere colonization of pepper and cucumber plants in relatively looser soil. When the ratio of clay and sand are 1 to 1 and 1 to 2 respectively, the density of colonization is significantly higher than that of other soil. On the 30th day of transplanting, the colonization density of rhizosphere soil and colonization density of the roots reached more than 10~6cfu/g and more than 10~5cfu/g respectively in the previous ration of soil. In the rhizosphere soil, colonization of S. plymuthica A21-4 is affected by soil temperature, however, the colonization density of plant roots is not obviously affected. Lower temperature would be helpful for the colonization of S. plymuthica A21-4 in the rhizosphere soil. When the soil temperature was 15 and 20 degrees, the colonization amount of S. plymuthica A21-4 was the highest in the rhizosphere soil, nearly reached 10~6cfu/g. Furthermore, soil moisture also had a significant effect on the colonization of S. plymuthica A21-4 in the rhizosphere soil and plant roots. Lower soil moisture would be helpful for the colonization of S. plymuthica A21-4. When the soil moisture was 20% and 40%, the colonization density of S. plymuthica A21-4 in the rhizosphere soil and plant roots were significantly higher than that of other soil moisture conditions, and the colonization density declined more gently, which was suitable for the growth and development of pepper and cucumber. In chemical environment, different pH values of soil would greatly affect the colonization of S. plymuthica A21-4 in the rhizosphere soil and plant roots. In the neutral and slightly acidic soil, the colonization density of S. plymuthica A21 -4 reduced slowly in the rhizosphere soil of pepper and cucumber plants. On the 30th day of transplanting, the colonization density of the soil rhizosphere nearly reached 10~6cfu/g. Meanwhile, the colonization density of the roots in the neutral and slightly acidic soil was also higher than that of other soils, and nearly reached 10~5cfu/g on the 30th day of transplanting. Moreover, having organic matter would be also helpful for the colonization of S. plymuthica A21-4, for example, after adding decomposed straws, its colonization was clearly improved in the rhizosphere soil and plant roots.In micro-ecological environment, having indigenous micro-organisms would be conducive to the colonization of S. plymuthica A21-4 in the rhizosphere soil and plant roots. In the natural soil, the colonization density of S. plymuthica A21-4 was higher than that of the sterilized soil conditions in the rhizosphere of pepper and cucumber plants. Furthermore, the existence of pathogen (Phytophthora capsici) in soil also promoted the colonization of S. plymuthica A21-4 in the rhizosphere soil and plant roots.