EFFECT OF SOIL-WATER STRESS ON STOMATAL-RESISTANCE AND LEAF WATER POTENTIAL OF RUBBER TREE SEEDLINGS

The effect of soil water stress on leaf water potential, stomatal resi stance and the recovery in leaf water potential after a severe water s tress was studied for rubber tree seedlings (Hevea spp.), using open p ollinated progenies of IAN 873, IAN 713, RRIM 600, and adult seedlings of Hbr. The seedlings were grown under controled conditions and expos ed to a gradual soil water deficit by withelding irrigation. At high v alues of soil water content, stomatal resistance for IAN 713 and IAN 8 73 were similar but lower than the stomatal resistances for RRIM 600 a nd Hbr. As soil water content decreased substantially stomatal resista nce increased up to 10 times but an inversion in the stomatal resistan ce for IAN 713 and Hbr progenies was observed. After being exposed to water stress for a few days, leaf water potential showed a daily fluct uation suggesting some internal changes in the mechanisms of water tra nsport and transpiration. It was observed that even under water stress leaves from IAN 713 and Hbr progenies kept higher values of leaf wate r potential. Leaf water potential recovery after a severe water stress was never complete indicating some osmotic adjustment for such plants .