Studies upon the copper fungicides; the penetration of copper into germinating peas

Three varieties of pea seed showed less damage when treated with solutions of simple cupric salts than with solutions of equivalent strength in which the copper could occur in complex form. On adding supplementary pea exudate to copper sulphate solution, thereby converting some cupric to complex copper, greater damage was caused. In spite of the greater phytotoxicity of complex forms of copper, the copper intake by the seeds was less. Sealing of the micropyle had little effect on the water and copper intake of peas.

Colorimetric tissue tests on treated peas indicated a high concentration of copper in the testa and the embryonic radical with only small amounts in the cotyledonary tissues. These observations were largely confirmed by chemical analyses‐on the test as, cotyledons and embryos of copper treated peas.

The results suggest that when copper dissolves from dressings on pea seeds much becomes fixed on the testa, so providing fungicidal protection. The soluble complex forms of copper produced by pea exudate are markedly phytotoxic and injury to the embryonic radical is regarded as the main cause of damage to peas.

Studies upon the copper fungicides; the solution of copper from dressings on the pea seed

During the process of swelling pea seeds yielded substances to water which were capable of dissolving the insoluble copper dressings normally applied to the seed to prevent ‘pre‐emergence damping off’. This occurred under conditions in which soil factors were eliminated and irrespective of whether the dressing was on the surface of the seed or treated separately. Copper was readily taken into solution from dried 4:4:50 Bordeaux Mixture by water in which peas had been soaked, a circumstance which proved that the formation of soluble complex forms of copper was involved.

A chemical investigation on the solution obtained by soaking peas in water showed that volatile acids or their salts were present together with a protein‐like material in colloidal solution. The occurrence of amino derivatives and other nitrogenous materials as well as carbohydrates was indicated and evidence of the presence of asparagine and citrate was also obtained.

The suggestion is made that both the fungicidal and phytocidal actions of insoluble copper dressings on pea seed depend largely on the effect of the pea seed exudates, notably colloidal protein‐like material and certain amino derivatives, in bringing copper into solution.