Effect of water stress on flower-bud formation and plant hormone content of satsuma mandarin (Citrus unshiu Marc.)

The effect of water stress on plant hormones (GAs, IAA and ABA) level in the leaves and flower-bud formation of the satsuma mandarin (Citrus unshiu Marc.) trees was investigated to determine the relationship between flower-bud induction and the level of endogenous plant hormones as a result of water stress. Severe water stress (-1.5 to -2.0 MPa) in autumn, which causes heavy leaf fall, reduced the percentage of flowering nodes by one third of the moderately water-stressed ones (-0.5 to -1.0 MPa). The quantity of GA(1/3) from the middle of October through early December was significantly higher in the leaves of the trees under severe water stress than in the leaves of the trees enduring moderate water stress. The content of IAA in the leaves of the trees under moderate water stress was higher in late February. These findings indicate that the levels of GA(1/3) are enhanced by severe water stress, higher in the leaves from the branches that produce fewer flowers during flower-bud induction periods. The levels of IAA were higher in the leaves from the branches that produced more flowers during the season when flower-buds develop. (C) 2003 Elsevier B.V. All rights reserved.