P. GEERTS¹, A. BULDGEN¹, T. DIALLO² and A. DIENG²

¹Unité de Zootechnie, Faculté Universitaire des Sciences Agronomiques, Gembloux, Belgium
²Département des Productions Animales, Ecole Nationale Supérieure d'Agriculture, Thiès, Senegal

Abstract

Leaf water potential (Ψl) and osmotic potential (π) in 6 Senegalese local strains of Andropogon gayanus var. bisquamulatus were studied during the rainy season of 1995 (July–September) under the Sahelo-Sudanese climate (Thiès, Senegal). Strains were chosen according to their phenotypic diversity and vigour. During the experiment, soil volumetric water content (SVWC, % volume) decreased from 22% to 8%. Each day of measurements, 3 replicates of 9 plants per strain were studied. At the end of the experiment, leaf hairiness, length and width of leaves, length of stems, number of tillers and height and diameter of plants were measured, using 3 replicates, on each strain at the 5–6 leaf stage.
No significant difference (P > 0.05) appeared between the strains in Ψl and π when the SVWC was higher than 15%. During a drying cycle, at the end of July, mean values of Ψl and π decreased in a 13-day lag, respectively, from –0.5 MPa and –1.5 MPa to –1.5 MPa and –2 MPa. Logarithmic models were fitted for the hydric parameters of each strain and the constants of the models were subjected to a one-way analysis of variance. Significant differences (P < 0.05) were observed between strains and 3 groups were identified according to their capacity for osmotic adjustment. The π adjustment (expressed at full turgor) was correlated with: a drought resistance index (DRI), involving DM concentration and sap osmolality of the leaves; and morphological characteristics of the strains (higher osmotic adjustment was related to narrower leaves and abundant pilosity).
This study confirms the capability of active osmoregulation in the var. bisquamulatus and underlines the high intravarietal variability of the Senegalese ecotypes. The capacity for osmotic adjustment may be used as a criterion when selecting for drought resistance. In this perspective, a selection strategy, which combines measurements of leaf width and a DRI, is proposed.