Study On The Dynamic Infection Process Of Soft Rot Disease In Konjac And Its Control Based On Quorum Sensing

Konjac (Amorphophallus konjac), a perennial herbaceous crops of Araceae, is widelycultivated because of its abundant konjac glucomannan. However, soft rot have become acommon disease during konjac planting, which restrict severely the development ofkonjac industry. The occurrence of soft rot is under quorum sensing (QS) control.Phytopathogens regulate expression of some virulence determinants, such as exoenzymes,according to the accumulation of signal molecules AHLs synthetized by cells. Anabundance of exoenzymes are secreted to the extracellular of the pathogens to destroy thecells of konjac, which lead to the tissue maceration and death. In this work, the isolation,identification, and the pathogenic factors of the pathogens from soft-rot konjac werediscussed. Moreover, the infection process of soft-rot disease in konjac was studied, andthe quorum sensing and quorum quenching of pathogens were also studied to explore theoutbreak mechanism and control of this disease. The main results were shown as follows:(1) Soft rot pathogens ZX-1and ZX-2were isolated and identified as Erwiniachrysanthemi (Ech) through pathogenicity tests, physiological detemination and16SrDNA analysis. Erwinia carotovora ssp. carotovora ES09isolated before was used as thecontrol. It is suggested that the three pathogens showed higher growth speed and strongerpathogenicity under evaluated temperatures, and produced obvious exoenzymes. Besides,ES09was inoculated into konjac tubers and incubated at22℃,28℃and35℃todetermine the size of the populations of bacteria in the tissues. The results of the fastestmultiplication of ES09at35℃explained that ES09macerated konjac tuber muchstronger while the exoenzymes production changed slightly under evaluated temperatures.(2) A recombinant Erwinia carotovora ssp. carotovora tagged by green fluorescentprotein was constructed and named as ES09-GFP. The infection process of soft-rot diseasein konjac was studied through the distribution of ES09-GFP in the plants of konjac and thechanges of structure of konjac tissues. The results suggested that Erwinia could invadekonjac through the wounds of konjac, and move vertically or laterally by the rich vascularsystem. Then, the gradual degration of vascular cells, parenchyma cells, sclerenchyma cells and cortical cells by exoenzymes occured after the pathogens’ biomass met thethreshold followed by konjac tissues collapse and soft rot, which confirmed the quorumsensing of pathogens of konjac.(3) Two bacterial biosensors Agrobacterium tumefaciens136and Chromobacteriumviolaceum V026were used to dectect the AHLs synthetized by Erwinia. The AHLsproduced can induce the quorum sensing of A136but cannot induce that of CV026,further confirming the quorum sensing of pathogens of konjac. Moreover,5antibioticswere used to quench the pathogens’ quorum sensing. The concentration of50~100μg/mLneomycin and spectinomycin showed strongest quenching effect to Erwinia, in whichA136showed no color. The effect of erythromycin was second, and the concentration of1~100μg/mL gentamicin and tobramycin showed little effect. The results mentionedabove suggested that the antibiotics could be used as quorum quenching chemicals toalleviate the soft-rot disease in konjac.