In‐vivo efficacy and in‐vitro activity of tubercidin, an antibiotic nucleoside, for control of Phytophthora capsici blight in Capsicum annuum

The antibiotic nucleoside tubercidin produced by Streptomyces viola‐ceoniger was evaluated for in‐vivo efficacy and in‐vitro activity against Phytophthora capsici, Magnaporthe grisea and Colletotrichum gloeosporioides. Tubercidin was more effective against P. capsici and M. grisea than against C. gloeosporioides in inhibiting mycelial growth. The bioassay on TLC plates was the most sensitive method and allowed the evaluation of antifungal activity of tubercidin even at a low concentration of 0.1 μgml⁻¹. As compared to the systemic fungicide metalaxyl, tubercidin was similar or somewhat higher in inhibition of mycelial growth of P. capsici. When applied to pepper stems, tubercidin was equally as effective as metalaxyl in the control of phytophthora blight in pepper plants, irrespective of application time and concentration. The treatment with 1000 μg ml⁻¹ tubercidin induced phytotoxicity in pepper plants. No control efficacy of phytophtora blight was observed in pepper plants supplied with a soil drench of tubercidin. Treatment with tubercidin at 500 μg ml⁻¹ completely protected pepper plants at first branch stage from phytophthora blight until four days after application. The control efficacy of tubercidin drastically declined seven days after application.