| The biocontrol effects,applying methods and biocontrol mechanism of the five obtained bacterium strains with good potential biocontrol function and the multiple biocontrol agent AR98 composed of them against pepper bacterial wilt and cucumber phytophthora blight were studied respectively ,based on the studies on screening and using methods of biological control bacteria of plant soilborne diseases,and the five biocontrol bacterial strains were identified according to the morphological ,physiological and biochemical characterestics.One hundred bacterial isolates were obstained from the rhiszosphere of pepper.tomato and cucumber in vegtable-field soil of Nanjing and Huaiyin of Jiangsu Province and Fugou County of Henan Province from 2000 to 2001.From the isolates 10 strains with obvious inhibiting activity to pathogens and the root-colonizing density are higher than 104cfu/g root were screened as the biocontrol microbes by using the method of the inhibiting zones combined with root-colonizing capacity of the ten isolates.Five strains with complementary function and affinity were selected and mixed as biocontrol agents AR98 for the control of pepper bacterial wilt and cucumber Phytophthora blight.Influence of five single and multiple biocontrol agents on the germination rate of pepper seeds and the seedling height of pepper were investigated. The germination precent of pepper seeds treated with AR98 suspension and five single bacterium suspension were 85.7%(AR98), 74.3%(Ri,F3,R6), 65.7%(Ji), 82.9%(G6)respectively,with that of the untreated control(CK)being 74.3%.The seedling height in the treatments of AR98, R1,F3,Re, J1, G6was 2.21, 1.19, 1.35, 1.11,0.76 and 1.21 times higher than that of the CK,respectively.The results showed that Ri^.Re.Ge and AR98 could improve the germination precent of pepper seeds and the growth of plants,with the effects of AR98 more obvious ,but that Ji strain had certain inhibiting effect to the seed germinating rate and the plant growth.In the greenhouse tests,the biocontrol effectiveness of the multiple agent AR98,single bacterium suspension Ri,F3,Ji,R6 and G6 to pepper bacterial was 91.1%,88.9%,80.5%,80.5%,66.7% and 57.0% respectively by soking roots,with that of AR98 the highest.The influences of different concentration and different applying methods of AR98 on biocontrol efficiency of pepper bacterial wilt were studied.The resultsshowed that the effective concentration of AR98 was more than 2 X 108cfu/ml ,and the most effective concentration 2x109cfu/ml, with the control effectiveness being 91.1% when the population density of the pathogenic bacteria(Ra/stotiia solanacearum) was 2 X 106cfu/gsoil in greenhouse.The treating ways of AR98 influenced the biocontrol efficiency to pepper bacterial wilt .The control effectiveness of AR98 was highest by soaking roots combined with drenching roots ,next by soaking roots,and the smallest by drenching roots.The colonizing capacity of AR98 on roots of pepper was determined. The colonizing population of AR98 in the sterilized soil and the natural soil were all higher than 107cfu/g root 16 days after soaking roots and planting, but reduced to 2.6x106cfu/g root and 1.2x106cfu/g root 30days after soaking roots and planting ,then increased to 3.4x106cfu/g root,3.9x106cfu/g root after 45 days,and reduced to 2.6x105cfu/g root,4x 105cfu/g root after 60 days, respectively.The results indicated that the root-colonizing ability of AR98 was all strong in the sterilized soil and in the natural soil,and the difference of root-colonizing population was small between in the sterilized soil and the natural soil.The influence of AR98 on the colonzing population of HL5(R.solanacennn) on pepper roots was determined to explore the mechanism of AR98 controling pepper bacterial wilt. The root-colonzing population of HLs reached to 3x108cfu/g root 8 days after root-soaking by water when some pepper were wilted, and the population of HL5 increased to 1.1x109cfu/g root 30 days after soaking roots and planting when all pepper plants were wilted.But by... |
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