The effect of several inorganic elements contained in B5 medium on Phytophthora stem rot disease reduction of Glycine max (L.) Merr. cv. Chusei-Hikarikuro was investigated using the agar medium inoculation method. Application of B5 solution prior to inoculation significantly inhibited infection compared with controls. The incidence of disease of cv. Chusei-Hikarikuro with and without B5 was 40.0% and 97.6%, respectively. Several levels of macro inorganic nutrients (A), micro inorganic nutrients (B), Fe-EDTA solution (C) and organic elements (D) in B5 were applied in an effort to evaluate disease suppression. The concentration of 100% and 250% of A element was effective in inhibiting infection, with an incidence of disease of 17.9% and 54.6%, respectively. On the other hand, 10% of A together with three other nutrients (B, C and D) was ineffective, where the incidence of disease was 74.3-97.6%. Four media (A+B+C, A+B+D, A+C+D, and B+C+D) were also tested. Although the incidence of disease increased when medium (B+C+D) was used, it decreased significantly when media containing A was applied. Various concentrations (0, 10, 100, 250, 500 and 1000%) of KNO3, (NH4)2SO4, MgSO4, CaCl2 and NaH2PO4 in the presence of A nutrients was investigated in an effort to determine the elements most effective in suppressing the incidence of disease. A concentration of 10–1000% CaCl2 greatly inhibited infection, where the incidence of disease was 5.6-42.1%. A concentration of 100% KNO3 led to marked suppression of disease. However, concentrations of 10-500% of (NH4)2SO4, Mg4SO4 and NaH2PO4 induced disease at the same level as that of controls.
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