The Antagonistic And Biocontrol Effect Of Five Biocontrol Bacteria Strains Against Apple Replant Disease

With the variety renovation and cultivation mode changing speeding up in the main apple producing areas of China, the effect of replanted barriers become more and more serious. To improve soil microecology by introducing biocontrol microorganisms have been used as an important method to control apple replant disease.Four biocontrol bacteria strains Bs-0728, Bs-84, Bl-105 and X1015 that isolated previously, and another bacterial strain SS101 which was obtained from the Netherlands were tested in the present research. The in vitro antagonistic effect and growth promoting effect of the five bacteria strains have been tested in this research. Plate confrontation essay, mycelium growth rate essay and spore germination methods were used to test the antagonistic effect of the biocontrol bacteria strains in vitro. The inhibitory effects of the five antagonistic bacteria strains against pathogenic fungi of apple replant disease (ARD) were confirmed. To test the effect on seed germination, radicle elongation of Malus robusta, the effect on the growth and survival rate of four-week seedlings, one-year M. robusta plants and two-year M. pumila plants, the growth promoting and biological control effect of five biocontrol bacteria strains were confirmed. To develop new biological control agents, the solid state fermentation condition of Bs-0728 was optimized. The results of all the research are as follows:1. Five biological control bacteria strains have different inhibitory effect against the tested 19 ARD pathogenic fungi isolates. The Bacillus subtilis strain Bs-0728 showed the best inhibitory effect and the widest inhibition spectrum against 19 ARD pathogenic fungi isolates among the tested five antagonistic strains. Bs-0728 showed not only competition effect, but also direct inhibitory effect against the pathogenic fungi mycelia growth. Bs-0728 and SS101 he best inhibitory effect and the widest inhibition spectrum against 19 ARD pathogen fungi isolates on spore germination among the tested five antagonistic strains. The antagonistic bacteria strains did not show significant difference against the pathogenic fungi isolates isolated from different apple production region. While the antagonistic strains showed significant difference against diffent pathogenic fungi species. The inhibitory effects of the antagonistic strains were especially strong against Fusarium spp., but the effects were relatively weak against Alternaria spp.2. The appropriate medium for solid state fermentation ratio of Bs-0728 was"wheat bran:corn stalk powder:corn flour as 3:4:2". The suitable culture period was 48 hours. The optimum fermentation temperature was about 28~30℃. The optimum initial moisture content was 250%. The optimum initial pH was 8.0.3. Bs-0728 and X1015 treatments facilitated the seed germination effect of M. robusta, the germination rate reached 86.7%, increase by 14.7% compare with that of untreated control. SS101, Bl-105 and Bs-0728 significantly promoted the radicle elongation of M. robusta, the radicle length was separately 42.55%, 35.91% and 33.67% longer than that of untreated control. Replanted soil was treated with the solid fermentation products of five biocontrol starins in pots separately, and the four-week M. robusta seedlings were transplanted on the treated soil to test the control effect of the strains on ARD. Four-week M. robusta seedlings were used to test the biocontrol effect of five antagonistic bacteria strains in pot experiment. Result of the seedlings survival rate showed that the soil replacement treatment had the highest survival rate 100%, and secondly was Bs-0728 treatment with the survival rate 77.8%, the survival rate of the replanted soil treatment was zero. When measured the plant height, the soil replacement treatment facilitated the plant growth, the plant height increased 14.6 mm within two weeks, and the plant height increase of the antagonistic bacteria treatment Bs-0728 and SS101 was 7.2 mm and 5.6 mm respectively, while that of negative control was only 3 mm within two weeks growth period. The dry weight of the seedlings was used to measure the biomass. The soil replacement treatment showed the best control effect against the negative control, the biomass increased 136.9%, 138 inocula and Bs-0728 treatments increased 80.3% and 63% separately compare with the negative control.Pots planted one-year M. robusta and two-year M. pumila plants were treated with five biocontrol strains in the field to test their plant growth promotion and disease control effect. Bs-0728 and SS101 treatments showed significant promoting effect either on plant diameter increase or on diameter increase rate compare with negative control.