The influence of naphthalene acetic acid (NAA) on tipburn of internal leaves of lettuce (Lactuca sativa L.)

Abstract

NAA potassium salt (preparation Pomonit) applied at a concentration of 25 mg·dm;^-3 markedly inhibited tipburn of internal leaves in lettuce plants grown in a greenhouse. Reduction of tipburn symptoms ranged from 9.6 to 96.9% depending on the cultivar. In the internal leaves, on which the disorder usually appears, the calcium level was generally lower and the level of phenolic substances higher. Treating the plants with a potassium salt of NAA, 2-3 weeks before harvest usually caused a rise of the Ca⁺⁺ level and a decrease in the level of phenolic substances in the internal leaves. The NAA potassium salt was rapidly degraded in the plant and after only 24 hours was almost undetectable by a method sensitive to 0.3 µg NAA·g^-1 fresh matter, therefore it is probable that NAA treatment may be permitted in practice.