Induction of root browning by chloramine in Lactuca sativa L. grown in hydroponics

The cause of root browning (RB) in Lactuca sativa L. root, which often occurs in hydroponics when a nutrient solution is prepared with tap water, was investigated. The induction of RB occurred only when plants were cultured in the solutions containing both hypochlorous acid (HOCl) and ammonium ion (NH4+), but not in the solutions contained either HOCl or NH4+ alone. The addition of NaOCl (HOCl) followed by NH4H2PO4 (NH4+) solution after a 7-10 day storage or NH4H2PO4 followed by NaOCl solution induced no RB symptom. It was concluded that RB was induced by chloramine, a reaction product between HOCl and NH4+. Dechlorination of nutrient solutions was promoted in the presence of the iron ion in the solution under light conditions.