Induction of systemic resistance in turmeric by rhizospheric isolate Trichoderma asperellum against rhizome rot disease

he rhizospheric fungal isolates were screened for growth promotion and induced systemic resistance against rhizome rot disease in turmeric caused by Pythium aphanidermatum (Edson) Fitzp. Thirty isolates from the turmeric rhizosphere were identified by morphological characteristics and using internal transcribed spacer sequence homology. In in vitro antagonistic activity, out of 30 isolates tested only five isolates showed >70% suppression of P. aphanidermatum. The rhizospheric isolates viz., T. viride PGPFDOB-V6, Chaetomium sp. PGPFDOB-V13, T. asperellum PGPFDOB-V11, T. harzianum PGPFDOB-V22 and T. asperellum PGPFDOB-V36 also showed multiple plant growth promoting traits under in vitro studies. In greenhouse studies, rhizome treatment followed by soil application of PGPFDOB-V36 significantly increased the plant height to 87.60 cm and fresh rhizome yield/plant to 430 g. This isolate reduced the percent disease incidence (PDI) of rhizome rot to 14.2% when compared to the control 78.70%. The rhizome colonization of PGPFDOB-V36 was observed by using the confocal microscope. The selected PGPF isolates were tested for their ability to induce production of defense-related enzymes in plants. Temporal expression pattern of defense-related enzymes such as peroxidase (PO), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and PR-protein β-1,3 glucanase in turmeric plants pretreated with PGPF isolates followed by challenge inoculation with the pathogen was studied. The defense enzymes were increased by two to three folds compared to uninoculated control. The accumulation of phenolics was higher in plants pre-treated with the PGPF isolates. The study revealed that the rhizosphere isolate PGPFDOB-V36 has promising plant growth promoting and rhizome rot suppression ability in turmeric.