Effects Of Herbicide Diclofop Methyl On Rhizosphere Microorganism And Systemic Aquired Resistance In Rice

Herbicides,one of the crucial factors in a worldwide,can increase agricultural production,but their residuals in environment may bring in adverse impacts on nontarget species,including humans.The effect of herbicide on rhizosphere microbial community is an important research field for environmental toxicology.Studying the effect of herbicide on rhizosphere microorganism and systemic acquired resistance became a more important topic at present.Diclofop-methyl,a wildly used aryloxyphenoxypropionate herbicide,can be easily absorbed by the plant root,stem and leaf.Japonica rice‘Xiushui 63'seedling was selected in the study and used to research the effects of DM on rice rhizosphere microorganism and systemic acquired resistance.The results showed that the number of 16S rDNA copy in per weight of roots increased to 1.1×10¹²,about 3.14-fold of the control after 5 d of 100?g/L DM treatment,which implicatedthattheabundanceofrhizospheremicroorganism significantly increased.The results of Metagenomic 16S rDNA Illumina tags uncovered that DM treatment also influenced the community structure of microorganisms.Massilia became the advantage bacterium group,and the relative abundance of Hydrotaleaand and Sphingomonas increased,while Streptococcus,uncultured-Comamonadaceae,Bradyrhizobium and Candidatus Xiphinematobacter decreased after DM treatment.The secretion of exogenous malic acid and oxalic acid increased significantly after DM treatment,which was one of the main reasons to change the community structure of microorganisms.The results also showed that the transcript abundance of SA-dependent resistance genes PAD4 and EDS1were up-regulated by the DM treatment.And the SA mediated key regulatory factor NPR1,SAR marker gene PR1a were also up-regulated to occur SA signal pathway,the transcrips of key genes in jasmonic acid?JA?signal pathway were not affected obviously.Bacterial abundance,community structure in the rhizosphere could also be affected by direct toxic effect of DM on bacteria in the rhizosphere.The precise mechanism?s?explaining the effect of DM on the bacterial community structure in the rhizosphere and SAR revealed in this study are important because it is expected to affect plant nutrition and plant resistance and perhaps indirectly modulate DM toxicity in plant.