Study On The Outbreak Mechanism Of Soft-rot Disease In Konjac And Its Biocontrol Based On The Resistance Inducement

Konjac (Araceae Amorphophallus) is a perennial economical crop rich in active ingredients including konjac glucomannan which is in urgent need in food, medicine and chemical industry. Thus, konjac is widely cultivated in the southwest of China. However, as the soft-rot disease break out every year explosively and contagiously when the temperature rises dramatically in the summer, this disease has developed into a devastating catastrophe to konjac production. In this work, pathogen responsible for the soft-rot disease in konjac was isolated and identified; the physiological and pathogenic factors, such as growth and pathogenicity, were studied under different temperatures to understand the outbreak mechanism of this disease under evaluated temperatures; 6 externally applied chemical activators to plant defence system were also studied to explore their potentical as soft- rot resistence inducer. The main results were shown as follows:(1) Soft-rot pathogen ES09 was isolated and identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) through 16s rDNA blast and physiological tests.(2) It is suggested that ES09 showed higher growth speed and stonger motility when the temperature was evaluated above 30oC. Denaturing gradient gel electrophoresis (DGGE) revealed, compared to May and November, the population of ES09 in the konjac rhizosphere increased significantly in July.(3) It is suggested that ES09 macerated konjac tuber much stronger under 30oC and 37oC with the pathogenicity test. Excellular enzyme production was strictly regulated under quorum sensing, pectate lyase and polygalactronase was producted in high levels only if the bacteria population met the threshold.(4) The potential of 6 externally applied chemical resistence activators were tested on the konjac leaves cultivated in the lab and plants in field, revealing the infection of ES09 was inhibited in salicylic acid (SA), p-coumaric acid (p-CA), and cinnanamic acid (CA) treated leaves or plants; compared to the control, more excellular H2O2 accumulation and higher peroxidase activity were observed in SA, p-CA and CA treated leaves, suggesting these leaf-spraying chemicals could take effect in the oxidase burst of konjac cells, resisting the attack from the soft-rot pathogen.