Plant Growth-Promoting Rhizobacterial Strain-Mediated Induced Systemic Resistance in Tea (Camellia sinensis (L.) O. Kuntze) Through Defense-Related Enzymes Against Brown Root Rot and Charcoal Stump Rot

Induction of systemic resistance in host plants through microbes and their bioactive metabolites are attaining popularity in modern agricultural practices. In this regard, individual application of two strains of Pseudomonas, RRLJ 134 and RRLJ 04, exhibited development of induced systemic resistance in tea plants against brown root rot and charcoal stump rot under split root experiments. The experimental findings also confirmed that the cuttings treated with fungal test pathogen and plant growth-promoting rhizobacteria (PGPR) strains survived longer as compared with pathogen–alone-treated cuttings. The enzyme level studies revealed that the presence of PGPR strains reduced the viscosity loss of cellulose and pectin by both the pathogens to a significant level. The activity of defense-related enzymes like L-phenylalanine ammonia lyase, peroxidase, and polyphenol oxidase were also recorded higher in tea cuttings treated with PGPR strains in presence of pathogen. Crude bioactive metabolites isolated from these strains also showed in vitro antagonism against the test pathogens besides reducing the number of diseased plants under gnotobiotic conditions. These findings confirm the utilization of these two strains for induction of systemic resistance against two major root diseases in tea plants under plantation conditions.