THE RELATIVE IMPORTANCE OF FACTORS CAUSING INJURY TO SHOOTS OF FLOODED TOMATO PLANTS

Abstract

FLOODING THE root systems of many herbaceous species which have been growing in well-aerated soil results in characteristic symptoms of injury to the shoots. These symptoms are epinasty, chlorosis and wilting of leaves, reduction in rate of shoot elongation, and formation of callus tissue and adventitious roots along the stem at or near the water line. As Kramer (1951) has pointed out, these symptoms cannot be due entirely to a water deficit in the shoot caused by decreased absorbing capacity of the root system, because some of the symptoms develop only in turgid shoots. This is true of epinasty of the leaves, and callus and adventitious root formation along the stem. The usual sequence of development of injury symptoms in plants whose root systems growing in soil are flooded is (1) wilting of leaves within a few hours, (2) severe epinasty of middle leaves and reduction in rate of shoot elongation by the following day, (3) callus formation and adventitious root emergence in 4-5 days, and (4) chlorosis of lower leaves. During the early part of the treatment period (first 3-4 days) the wilted shoots recover at night, but the shoots later fail to recover turgidity even at night unless the adventitious roots form an adequate absorbing system. This study was made to determine the relative importance of (1) an oxygen deficiency, (2) a carbon dioxide excess, and (3) microorganisms, their by-products, and debris from the dying roots in causing the injury symptoms exhibited by shoots following flooding of the roots. METHODS.-Root systems plus basal portions of the stems of intact Marglobe tomato plants approximately 15 in. tall, grown in soil, were subjected to the following treatments: (A) flooding with tap water continuously aerated with compressed air; (B) flooding with oxygen-free water; (C) flooding with oxygen-free water with nitrogen gas bubbled through the containers to remove excess carbon dioxide; (D) flooding with oxygen-free water which was drained and replaced every 12 hr. under oxygen-free conditions to decrease the concentration of carbon dioxide, other toxic substances, and microorganisms; and (E) flooding with continuously flowing tap water.