Trichoderma and agrochemical induced defensive metabolites for suppressing rust disease of faba bean in Bangladesh

Research investigations were conducted both in in-vitro and in-vivo with three potential strains of Trichoderma isolates ( Trichoderma harzianum AB935952, T. asperellum AB935955, and T. viride, Tv6 ); three agrochemicals viz. , Bion, Chitosan and Amistar Top (as positive control) during two cropping season (2019–2021) to manage rust disease of faba bean in Mymensingh district of Bangladesh. In vitro assay clearly revealed that 60% culture filtrate of T. viride; bion and Amistar top @ 60 mM inhibited 100% inhibition of uredial germination of Uromyces viciae fabae followed by T. harzianum and T. asperellum . Chitosan showed significantly the lowest inhibition of urediospore germination. Spraying of each Tricho-suspension (@10 ⁸ cfu/ml) and agrochemicals on faba bean plants in the greenhouse significantly decreased rusty spot severity where, Amistar top, T. viride and Bion were found to be the most effective treatments followed by T. harzianum and T. asperellum . Five treatments were found significantly effective in reducing the rust disease severity of faba bean comparing with control treatment under field conditions. In both cropping seasons, field experiments revealed that spraying of Trichoderma spp., Bion and Amistar Top on faba bean plants significantly reduced the rust disease severity and increased the agronomic parameters viz ., plant height (cm), no. of pods /plant, fresh wt (g), dry weight (g) and seed yield (kg/ha) compared with the control treatment. Among the three Trichoderma spp., T. viride showed the best performance in reducing rust disease severity (8.20% and 10.20%) with increasing faba bean yield (3240 and 3331 kg/ha) followed by Bion. Analysis of induced biochemicals, Bion resulted the highest activity of peroxidase (POX), polyphenoloxidase (PPO), and phenylalanine ammonia lyase (PAL), whereas, T. viride resulted the highest amount of total phenol and flavonoid. T. harzianum resulted the highest amount of β, 1–3 glucanase and total chlorophyll content. The least amount of bio-chemicals with higher rust severity was recorded in case of Chitosan. Thus, the increments of POX activity, total phenols, total flavonoids and seed yield revealed that T. viride is a promising antagonistic species of fungi that may be the alternate of chemical fungicides for management of rust disease in Bangladesh.