Plant growth promotion and induced defense response in safflower by Trichoderma

Abstract

Nine potential Trichoderma strains were tested for mycoparasitic, defence enzyme activity and root colonizing behaviour against Macrophomina phaseolina and Fusarium oxysporum f. sp. carthami in safflower ( Carthmus tinctorius L). Among them three strains viz., T. harzianum Th4d, T. asperellum TaDOR7316 and T. asperellum Tv5 were found to be most effective showing superior antagonistic activity. Hyphal interaction studies revealed that the inhibition was caused by an interaction that took place in close contact with the host hypha, causing lysis, swelling and coiling of mycelia resulting potentially reduced mycelial growth of M. phaseolina and showed lytic enzymes activity to various extent in Th4d, Tv5 and TaDOR 7316. These strains were also able to solubilize inorganic (P). Increased activity of defense related enzymes viz., peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activity in these three potential strains pre-treated safflower plants challenged with M. phaseolina was observed. PO, PPO and PAL activity was also increased two-three folds more in all these bioagents. Interaction between the bioagents and the safflower root system showed profuse adhesion of hyphae to the plant roots as well as colonization of the root epidermis and cortex cells but not the vessels at early stages of safflower root system. Levels of hydrogen peroxide (H₂O₂) in the bioagents treated leaves and untreated (control) were determined microscopically. Application of these bioagents under field conditions reduced the incidence of root rot and Fusarium wilt, increased growth and plant biomass to a reasonable extent with better root colonization, which is directly correlated with the resistance of the plant against infection and high seed yield, was observed with bioagents treatment. Thus, it is evident that the hyphal interaction and enzymes play a key role to stimulate the defense mechanism which aid in disease management as well as plant growth promotion of the host plant against pathogen attack.