SOME NUTRITIONAL DISORDERS OF THE TOMATO

Abstract

SUMMARY Blotchy ripening of tomato fruits is the result of malnutrition in respect of potash and nitrogen, especially the former. Phosphates seem to be unimportant in this respect. The proportion of blotchy fruits may be reduced to less than 1 per cent, by suitable applications of sulphate of potash and sulphate of ammonia. Blotchy ripening has not been eliminated entirely by manurial treatment. Other factors, probably climatic in nature, play some part in the incidence of this disorder. Root invading fungi, such as Colletotrichum tabificum, interfere with the feeding of the plant and indirectly cause blotchiness of the fruit. Exposure of the fruits to excessive sunlight causes a type of blotchiness known as “green back” if the nitrogen and potash supply is inadequate. Blotchy ripening may be accompanied by necrosis of the vascular bundles of the fruit and breakdown of the adjacent tissues with the formation of canals. A deficiency of nitrogen and potash in the soil in which tomato plants are growing causes distinctive colour changes in the leaf. The leaves of tomato plants grown in soil deficient in nitrogenous foods, develop pale yellow blotches between the veins. The blotches gradually increase in size until the entire leaf surface is yellow. Leaf scorch, characterised by a paling and subsequent desiccation of the leaf margin is due to potash starvation. When potash is absent from the nutrient supply, the severity of leaf scorch increases as the nitrogen and phosphate supply is increased. Leaf scorch can be eliminated completely by the application of sulphate of potash.