Untitled

Abstract

Leaf blight disease caused by Phytophthora colocasiae is the main constraint affecting taro plants in tropical and sub-subtropical countries. To control the disease, farmers commonly use chemical pesticides. Despite the efficacy of these chemical pesticides, their continued use is harmful to human and the environment. The alternative is the use of bio-control agents such as Trichoderma spp. The aim of this study was to evaluate the effect of Trichoderma harzianum (Edtm) and Trichoderma aureoviride (T4) as bio-control agents against P. colocasiae. The antagonism was evaluated by dual culture. The organic extracts were obtained by fermentation of each isolate of Trichoderma on potato dextrose broth (PDB). The chemical screening of the extracts was done and their efficiency on P. colocasiae was evaluated by poisoning method. The ability of the two antagonists to induce defense-related metabolites was done in pot experiments. In dual culture, the inhibition of the mycelia growth of the P. colocasiae was 34.77 and 41.77% for T. harzianum (Edtm) and T. aureoviride (T4), respectively. The organic extracts contained phenols, flavonoids, alkaloids, sterols and anthocyanins. Total inhibition (100%) of the mycelial growth of P. colocasiae was realized at 200 and 300µg/plug, respectively from T. harzianum (Edtm) and T. aureoviride (T4) organic extracts. In pot cultures, T. harzianum (Edtm) and T. aureoviride (T4) significantly reduced (49.4 and 46.4%, respectively) the necrosis of taro leaf blight. These strains significantly increased the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and polyphenol content in healthy and infected taro plants. These findings suggested that the use of T. harzianum (Edtm) and T. aureoviride (T4) could be a promising alternative to bio-control taro leaf blight.