Changes in the Distribution of Carbohydrates Due to Water Stress and Root-Shoot Ratio as an Index of Drought Resistance in Ecotypes of Adesmia bicolor (Poir.) D.C.
The genera Adesmia, is found in the “El Plata” area. Adesmia bicolor (Poir). D.C. is one of the most common species in Uruguay that belongs to this genera. In this study, three ecotypes were collected from different kinds of environments. Ecotypes 016, 2316 and 7017, came from superficial-soil, clay-soil and sandy soil, respectively. The ecotypes of Adesmia bicolor (Poir.) DC. were studied under water-stress conditions (two levels), during two stages: vegetative phase and beginning of blossom. In both stages, leaf-water potential (LWP), leaf-relative-water content (LRWC), leaf-dry matter (LDM), stem-dry matter (SDM) and root-dry matter (RDM) were measured, while root-shoot ratio [RSR=RDM/(LDM+SDM)] was calculated. During the first stage, ecotype 2316 was more affected by water stress (LWP = -2.238 MPa, LRWC = 49.248 %), while ecotypes 016 and 7017 were more tolerant to water stress (LWP = -1.600 MPa, LRWC = 82.120 % and LWP= -1.628 MPa, LRWC = 73.407 %, respectively). At this time we noticed a differential partition between LDM and SDM, without affecting the root-shoot ratio. Ecotype 016 under water stress, sent more carbohydrates to the stem rather than to the leaves, while in the ecotypes 2316 and 7017 there could not be found any difference in the partition associated with water stress. On the second stage, all the plants showed better hydric conditions; ecotype 2316 was the most sensitive ecotype (LRWC = 78.098 %) and ecotype 7017 was the least sensitive (LRWC = 89.448 %). However, ecotype 2316 showed good leaf and stem yields for both stages, even under the first water-stress cycle; while ecotype 016 was the least productive ecotype. Root-shoot ratio was associated with differences in the water stress resistance between ecotypes. On the first stage, RSR for ecotypes 016, 7017 and 2316 were 0.263, 0.224 and 0.197 respectively; on the second stage, ecotype 7017 showed the highest RSR (0.333). It is suggested that root-shoot ratio could be used as an index of selection towards drought resistance among those ecotypes. This ratio would not be influenced by temporary water stress conditions
