Production in Potato of Leaf Symptoms observed on Plants on Acid Soils together with Associated Tuber Necrosis

Abstract

POTATOES may respond visually in a complex manner to soil acidity^1,2, and many of these effects, including those of manganese or aluminium excess, calcium deficiency and potassium deficiency, have been reproduced in sand or water cultures^3–7. During an investigation of the interrelationships of iron, potassium and phosphorus in potato plants (var. Majestic) grown in sand culture, characteristic leaf symptoms hitherto seen only in the field under acid-soil conditions were observed. These appeared towards the middle of the season in the upper leaves. Leaflets showed pale yellow-green or whitish intervenal mottling at the base of the lamina in contrast to the apical and marginal regions, which generally remained normal green. Leaflets later became wavy and upcurled at the margin and, in severe cases, the basal region became chlorotic. A plentiful supply of readily available iron, provided either in solution or by increasing the availability of a low iron status with luxury concentrations of potassium⁸, appeared to be the main factor in producing these symptoms, even at the highest phosphate-level (8-9 milliequivalents/litre). Various combinations of manganese, aluminium, calcium and nitrogen levels tested in previous investigations of soil-acidity factors^3–5 did not reproduce the effect described here.