Salih, A.A., Soil and Water Research Center, Agricultural Research Corporation, P.O. Box 126, Wad Medani, Sudan
Ali, I.A., Arid Land Research Center, 1390 Hamasaka, Tottori 680, Japan
Lux, A., Dep. of Plant Physiology, Faculty of Natural Sciences, Comenius Univ., Mlynská dolina, 842 15 Bratislava, Slovakia
Luxova, M., Institute of Botany, Slovak Academy of Sciences, Dùbravská Cesta 14, 842 23 Bratislava, Slovakia
Cohen, Y., Institute of Soils and Water, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan, Israel
Sugimoto, Y., Arid Land Research Center, 1390 Hamasaka, Tottori 680, Japan
Inanaga, S., Arid Land Research Center, 1390 Hamasaka, Tottori 680, Japan

Several mechanisms have been proposed to explain the high tolerance of sorghum [Sorghum bicolor (L.) Moench] to drought. This paper reports a field study on the effects of soil moisture stress on the rooting habits, transpiration rate, and xylem anatomy of two sorghum cultivars, Tabat (drought susceptible) and Gadambalia (drought tolerant). Two levels of water stress, -0.02 MPa (wet) and -0.75 MPa (dry), were applied. Tabat had a higher root length density (RLD), higher late metaxylem (LMX) vessels per nodal root, higher leaf area, and higher transpiration rate than Gadambalia. In Tabat, soil moisture stress reduced RLD by 30%, nodal roots by 31%, number of LMX vessels in the root by 42%, leaf area by 13%, and transpiration rate by 11%. In Gadambalia soil moisture stress did not affect RLD at depths ≥0.2 m, number of nodal roots, or number of LMX vessels per nodal root. However, leaf area and transpiration rate were reduced by 3 and 11%, respectively. Under dry conditions, Gadambalia displayed a higher water extraction efficiency than Tabat throughout the profile (0-0.9 m). In Gadambalia, unlike Tabat, the stem was highly sclerified. A 1- to 3-cell-thick layer of schlerenchyana was observed beneath the epidermis. The peripheral vascular bundles were surrounded with a 3- to 6-cell-thick schlerenchyma sheath. However, in roots anatomical differences were less prominent. Drought tolerance in Gadambalia is associated with higher water extraction efficiency, fewer nodal roots per plant, fewer LMX vessels per nodal root, a smaller leaf area, and a well developed sclerenchyma.