Journal of Taiwan Agricultural Research

Author:Jyh-Nong Tsai, Pao-Jen Ann*, Ien-Tien Wang, Shin-Yuan Wang, and Chyung-Yue Hu

Abstract:

    The effect of the neutralized phosphorous acid solution (NPA) prepared with a simple method on suppression of Phytophthora infestans and control of potato and tomato late blight was evaluated.  The proposed method involved dissolving phosphorous acid in water before adding equal weights of potassium hydroxide.  NPA at a concentration of 1000 mg/L (a.i.) completely inhibited the mycelial growth and sporangial germination of P. infestans on rye B agar plates, while the inhibitory effects of NPA at lower concentration (100 or 10 mg/L) decreased dramatically.  The inhibition rates of mycelial growth and sporangial germination of P. infestans at 100 mg/L NPA were decreased to 21% and 69.9%, respectively, and at 10 mg/L NPA down to 0%.  When NPA at 1000 mg/L was foliar-sprayed to the plants of potato var. ‘Kennebec’ and tomato var. ‘Known-you 301’ for 2–4 times at 7 d intervals in the naturally infected fields in 1999–2000, the disease severity of Phytophthora late blight of both crops were significantly and effectively suppressed.  The disease reduction by 2 applications and 4 applications were 30.1% and 65.2%, respectively, for potato late blight, and 36.8% and 58.3%, respectively, for tomato late blight in comparison with the control.  Application of NPA at 1000 mg/L for 3 times every 6 weeks was also effective in suppression of tomato late blight, and thereby delay disease progress in the fields during the winter-spring seasons of 2004–2005.  The disease severity of both tomato varieties ‘Known-you 301’ and ‘Sen-nyu’ were 40–60% less than those without spray in the dry periods, whereas NPA treatments were only 20–40% less than controls during continuous rain.

Key words:Disease control, Phosphorous acid, Phytophthora late blight, Potato, Tomato

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