Evaluation of Hevea clones subjected to water deficits.

Six clones of Hevea were subjected to both continuous and cyclic dehydration treatments in order to evaluate their response with respect to photosynthesis, transpiration and stomatal resistance, to plant water status. The trials were carried out on young Hevea plants at eighty-five days after the stumps were transplanted in a greenhouse. The increasing soil dehydration influenced the clones differently by reducing the leaf water potential, transpiration and photosynthesis: and increasing the stomatal resistance. In some clones the cyclic soil dehydrationcaused significant reduction in the level of recovery of the transpiration rates and net photosynthesis up to the first and second water deficit cycle, respectively. For all clones, the leaf water potential decreased with the deficit cycles: and 48 h after re-irrigation the mean values of the pre-stress condition were fully recovered. The stomatal resistance increased with the cyclic water deficits. After re-irrigation a differential recovery of this parameter was observed. Consideringthe variables studied as a whole, clones IAN 3087 and IAN 6323 were less influenced by the imposed drought conditions, while FX 3899 was more sensitive