Lettuce Tipburn as Related to Nutrient Imbalance and Nitrogen Composition1

Preliminary analyses of lettuce showed that leaves with tipburn necrosis contained less Ca, and more organic N, particularly free amino acids, than normal leaves. A susceptible head lettuce, ‘Great Lakes 659’, was grown under varying NO 3 , Ca, Mg, and light intensities in the greenhouse and growth chambers. Tipburn was easily induced by a high NO 3 and low Ca nutritional regime. Five mM or more Ca in the nutrient solution prevented tipburn. Necrosis was aggravated by high Mg levels and high light intensities. This disorder was associated with an accumulation of free amino acids, particularly aspartic and glutamic acids, and their amides.