Although the fungicidal properties of copper were known as early as 1761, it was not until 1931 that copper was identified as an essential nutrient for plant growth. Copper is required for a range of different functions in plants, including production of viable pollen for grain production and maintenance of the cell wall structure. Additionally, Copper is an essential component of many proteins which are required for oxidation and reduction reactions within metabolic pathways such as photosynthesis, respiration and the regulation of plant hormones.
Winter cereals are less susceptible than spring cereals to drought-induced copper deficiencies as their root structure is better developed, allowing them to exploit micronutrients which sit lower in the soil. Oilseed rape is more tolerant of low levels of copper supply than cereals and so deficiencies are rarely observed. The offtake of copper in seed by oilseed rape is approximately a third of that of barley and a half of that of wheat and this could partly explain why oilseed rape is more tolerant of copper deficiency.
In wheat, both old and new leaves of plants which are copper deficient tend to show a withered appearance and are paler than non-deficient plants. One of the first symptoms of copper deficiency is ‘withertip’, which shows as a sudden dying and curling of the tip end of the leaf blade. The base end of the tip can remain green until senescence occurs. In wheat, shrivelled grains are also symptomatic of copper deficiency. Additionally, copper deficiency can lead to depositions of the pigment melanin, which can result in purpling of the stem and nodes.
Given that the sensitivity of oilseed rape to copper deficiency is low, it is unusual for deficiencies to occur. General symptoms of a lack of copper in oilseed rape include distortion, wilting, bleeding and death of the younger leaves. The whole plant phenotype resembles a plant suffering from water deficiency with permanent wilting and limp leaves.