Antisporulant activity of 8-hydroxyquinoline and its 5- and 6-n-alkyl derivatives against Gloeosporium fructigenum berk

The antisporulant activities of 8-hydroxyquinoline (oxine) and members of the homologous 5- and 6-n-alkyloxine series against Gloeosporium fructigenum at varying ambient pH values and in the presence or absence of added Cu²⁺, Zn²⁺ and Fe²⁺ are described. Whilst changes in the pH value only influenced the antisporulant activity of oxine at low concentrations, lowering the ambient pH increased considerably the activities of the 5- and 6-alkyl isomers at all concentrations. Below pH 7.0 the addition of these ions to the oxines resulted in decreased antisporulant activity (Fe²⁺ > Zn²⁺ > Cu²⁺) whereas, at pH 8.0, the addition of Cu²⁺ increased the activity of some oxines. It is suggested that at low pH (3.2) the oxine cation is an important toxicant.