Melanism and associated symptoms in wheat grown on copper‐responsive chalkland soils

Abstract

AbstractCopper applications increased yields and reduced ‘blackening’ symptoms of wheat grown on chalk rendzina soils (Icknield Series—organic phase) in southern England. The ‘blackening’ syndrome is recognised by an overall dark olive‐green colour of the plant and internodal melanism after ear emergence followed by ‘rat‐tailing’ of ears due to pinched or absent grains.The symptoms, which are aggravated by nitrogen applications, wet warm summers, and prior cropping with kale, have not previously been associated with inadequate copper nutrition. When Cu, Mg, Mn, Mo and Zn were applied to spring wheat grown in pots the only significant effects were from Cu and to a much smaller extent Mo. Soils where blackening occurred contained 3‐7 ppm total Cu and 0.4‐1.5 ppm extractable Cu (0.5 M‐EDTA). Yield increases of up to 200% were obtained both by foliar sprays of copper oxychloride (1 lb Cu/acre) or copper sulphate (0.2 lb Cu/acre) and by soil applications of copper sulphate (14 lb Cu/acre). Attempts to induce melanism in wheat plants grown in sand and water cultures with inadequate copper supply, high nitrogen levels, and small quantities of three amino‐acid melanin precursors were unsuccessful, although roots developed a dark pigmentation in certain of the treatments.