In-vitro inhibition of mycelial growth of several phytopathogenic fungi by soluble potassium silicate

Abstract

Soluble silicon has been reported to suppress some plant diseases, but in vitro inhibition of phytopathogenic fungi has not been demonstrated. In the current study in-vitro dose-responses towards soluble potassium silicate (20.7% SiO2) were determined for Phytophthora cinnamomi, Sclerotinia sclerotiorum, Pythium F-group, Mucor pusillus, Drechslera sp, Fusarium oxysporum, F. solani, Alternaria solani, Colletotrichum coccodes, Verticillium theobromae, Curvularia lunata and Stemphylium herbarum. Inhibition of mycelial growth was dose-related with 100% inhibition at 80 ml (pH 11.7) and 40 ml (pH 11.5) soluble potassium silicate per litre of agar, for all fungi tested with the exception of Drechslera sp. and F. oxysporum at 40 ml in one experiment. Only Sclerotinia sclerotiorum and Phytophthora cinnamomi were completely inhibited at all soluble potassium silicate concentrations between 5 and 80 ml.1−1 agar, while all the other fungi were only partially inhibited at potassium silicate concentrations of 5, 10 and 20 ml.1−1 agar. Percentage inhibition was positively correlated with dosage. Soluble potassium silicate raised the pH of unameliorated agar from 5.6 to 10.3 and 11.7 at potassium silicate concentrations of 5 and 80 ml.l−1 agar respectively. Subsequent investigations into the effect of pH in the absence of potassium silicate showed that fungal growth was only partially inhibited at pH 10.3 and 11.7. Clearly, potassium silicate had an inhibitory effect on fungal growth in vitro and this was mostly fungicidal rather than attributed to a pH effect.