Impact Of Rice Straw-Covering On The Incidence Of Wheat Sharp Eyespot And Rhizosphere Bacteria Community

Applying straw-covering is an effective measure for maintaining the fertility of soil. The research results indicated that the rice straw-covering could reduce the incidence of wheat sharp eye-spot. In order to define the effect of bacteria community and antagonistic substance in straw-covering field on the incidence of wheat sharp eye-spot, bacteria were isolated by plating count, the amount of 2,4-DAPG produced by fluorescent pseudomonads was analysed by FPLC and wheat sharp eye-spot was investigated. The results showed that the number of total bacteria and fluorescent pseudomonads was much higher in straw-covering soil than in no straw-covering soil. The effect of straw-covering on improving total bacteria and fluorescent pseudomonads in the earlier growth stage was greater than in the later growth stage. The production of 2,4-DAPG in straw-covering rhizosphere soil was more than in no straw-covering rhizosphere soil. The incidence of wheat sharp eye-spot in straw-covering soil was lower than in no straw-covering soil.To explicit the composition of rhizosphere bacteria which were antagonistic to Rhizoctonia cerealis and the effect of straw-covering on them, rhizosphere bacteria were isolated by plating count, antagonistic strains were screened, the ratio and inhibition width of antagonistic strains was measured, the proportion of fluorescent pseudomonads in total bacteria was counted and at last antagonistic strains were indentified. The results showed that among rhizosphere fluorescent pseudomonads isolated with selective Gould's medium, the ratio of antagonistic strains was above 80% and the mean inhibition width was above 0.87cm. Among total bacteria isolated with no selective medium, the ratio of antagonistic strains was about 50% and the mean inhibition width was about 0.7cm. In straw-covering soil. the proportion of fluorescent pseudomonads in total bacteria was 38-54%. In no straw-covering soil, the proportion of fluorescent pseudomonads in total bacteria was 30-37%. The results of strains identification showed that the ratio of Pseudomonas spp., Bacillus spp., Variovorax spp. was respectively 70%, 20%, 10% in straw-covering soil. In no straw-converin soil, the ratio of Pseudomonas spp., Bacillus spp., Variovorax spp.