INFLUENCE OF DEFRUITING ON THE ABSCISIC-ACID AND INDOLE-3-ACETIC-ACID CONTENTS OF COTTON LEAVES

A field experiment was conducted to test the hypothesis that young cotton (Gossypium hirsutum L.) fruits (bolls) serve as sinks for ABA, or that they are a source of IAA for subtending leaves. Cotton was grown in eight four-row plots in Phoenix during the summer of 1989 and irrigated about every two weeks. In one test, flowers at anthesis were removed on 22 and 29 June and on 7 and 14 July from the first node of fruiting branches of one center row, but not the other row, in each of four replications. Subtending leaves were harvested seven days after deflowering for ABA and IAA analyses. Removal of one flower per plant had no consistent effect on the concentrations of ABA and IAA in the subtending leaf. In another test, all flowers and bolls were removed from all plants of one center row, but not the other row, of four replications on 30 June and 5 and 13 July. Uppermost fully expanded mainstem leaves were harvested from the same plots on 20, 25, and 27 July, and on 9 August (7, 12, 14, and 27 days after final defruiting) for ABA and IAA analyses. Removal of all fruits apparently caused a slight increase in ABA concentration in mainstem leaves, but the effect disappeared with time after defruiting. The ability of leaves to accumulate ABA apparently decreased slightly as boll load increased. Complete fruit removal did not, however, affect the IAA content of leaves.