The combined application of Bacillus velezensis BCP6 and Jinggangmycin (JGM) to control soft rot caused by Pectobacterium aroidearum on Amorphophallus konjac

Amorphophallus spp. is an important group of crop and medicinal plants, but it is susceptible to infection by soft rot disease during both field growth and storage stages. This results in huge economic and yield losses, which must be properly addressed. Combined applications of Biological Control Agents (BCAs) and compatible chemicals have been recently considered as a more effective and reliable method to control bacterial soft rot. In the present study, we investigated the control effects against soft rot pathogenic bacteria Pectobacterium aroidearum MY11, using a BCA strain (i.e. Bacillus velezensis BCP6) and screening for three different bactericides, i.e. Jinggangmycin (JGM), Thiodiazole copper and Qingkulike. After exploring a joint application of BCP6 with chemicals, we found that JGM was the most effective and compatible bactericide to be compounded with BCP6. First, in the in vitro experiment, the mixture of JGM (34 mg/L) and suspension of BCP6 (1.0 × 108 cfu/mL) at 4:6 volume ratio performed with the strongest inhibitory effect on P. aroidearum MY11 (53.40%) and synergistic effect (1.78); this combination also significantly increased the biofilm production by BCP6, and constrained the swimming motility of P. aroidearum MY11 in agar plates and inhibited activities of cell wall-degrading enzymes. Second, the combined application of JGM and BPC6 reached up to 95.81% of control efficacy against P. aroidearum MY11 in a greenhouse experiment, and compared to JGM or BCP6 alone, combined application effectively increased konjac plant resistance to soft rot in the field, showing a synergistic action. Collectively, these results provided an alternative method for the management of soft rot disease in konjac planting.