Characterizing Root Responses to Low Phosphorus in Pearl Millet (Pennisetum glaucum (L.) R. Br.)

Adaptation to low water and soil P availability has been related to root properties. Two experiments were conducted in a greenhouse. Under hydroponics conditions, plants of the Souna 3 cultivar were grown for 30 d with three levels of P (P0 5 0.0 mol L21 ,P 15 0.073 1023 mol L21, and P2 5 1.65 1023 mol L21). In the pot ex- periment, two cultivars (Souna 3 and IBMV8402) were planted in pots filled with 19 kg of P-deficient and sandy soil and subjected to two watering regimes: well watered and water stressed at the vege- tative phase from 23 d after sowing (DAS) to 30 DAS. Phosphorus treatment consisted of two levels: application of phosphate fertilizer (P2O5) at the rate of 649 mg per pot (34 mg P2O5 kg21 soil), referred to as F1, and no phosphate application, referred to as F0. The results showed that under P deficiency, pearl millet (Pennisetum glaucum (L.) R. Br.) presented an alteration of root parameters, particularly root volume, by the formation of root hair. Under non-water-limited conditions as well as in high or low P, IBMV8402 showed a better root and shoot growth. However, under drought conditions, the leaf water potential (8f) of IBMV8402 (8f 52 5 MPa) decreased more than that of Souna 3 (8f 52 3 MPa). In spite of this, P supply improved the root and shoot growth of IBMV8402. Finally, except for the con- dition of water stress and without P supply, P utilization efficiency exhibited by IBMV8402 was 20 to 50% higher than that of Souna 3 on the basis of shoot biomass production.