Biological management of rhizome rot in ginger (Zingiber officinale ) plants and stored ginger seeds

Two endospore-forming endophytic bacteria (EEB1 A8 and EEB2 B13) were isolated from ginger rhizome collected from the fields of College of Agriculture, Vellayani and identified as Bacillus spp. Their antagonistic potential against Pythium myriotylum , the soft rot pathogen of ginger, was analyzed in vitro by dual culture plate assay and the agar well diffusion method. They tested positive for biocontrol traits such as the production of hydrogen cyanide, siderophore and volatile organic compounds. The bacterial isolates were applied to ginger plants to test biocontrol efficiency against P. myriotylum , individually and in combination with Piriformospora indica , a fungal root endophyte capable of promoting plant growth and enhancing plant defense. A lesser percent disease index (PDI) was observed in plants where the combination of EEB1 A8 and P. indica was applied. The activity of enzymes pertinent to protective mechanisms against pathogens, like peroxidase, phenylalanine ammonia-lyase, super oxide dismutase (SOD) and polyphenol oxidase (PPO) in the plants were analyzed before challenging, 1st, 3rd and 5th day after challenging with pathogen. The values followed the same trend in all treatments as it increased after inoculation up to 3rd day and then decreased for peroxidase (PO) and SOD. The plants treated with EEB1 A8 and combination of EEB1 A8 and P. indica showed the highest values for the level of defense enzyme production. In a storage study, when ginger seed rhizomes were treated with individual bacterial isolates and as a consortium of both, followed by inoculation with the pathogen P. myriotylum , rhizomes treated with consortium were more tolerant to rhizome rot. Applying endospore-forming bacteria with biocontrol properties is a propitious method for controlling rhizome rot in ginger, in the field and during seed storage.