EFFECTS OF PHOSPHORUS AND DROUGHT STRESSES ON DRY-MATTER AND PHOSPHORUS ALLOCATION IN WHEAT

The effect of phosphorus (P) and soil water availability (W) on the gr owth and development of wheat plants (Triticum aestivum L. cv. Minaret ) was studied in a pot experiment. Four levels of P supply (0, 15, 30, and 100 mu gP/g soil) were applied before sowing. Thirty-four days af ter sowing (DAS), the pots were kept near 100% of field capacity (FC). From 34 DAS until one week before anthesis (67 DAS), half of the pots were maintained between 60-70% FC. Control pots were kept at 85-95% F C by weighing and watering the pots every two to three days. Shoots we re harvested four times before anthesis and twice after. At each harve st, dry matter and P accumulation were measured in leaves, stems, and ears. In this study, thermal time until anthesis was inversely related to the level of P application. Phosphorus additioning affected the al location of biomass and P in aerial plant organs. Plants growing only with soil P showed a delay in the allocation of dry matter and P into leaves and stems with respect to plants fertilized with 100 mu g P/g o f soil. In this study, the final composition of the grain depended on re-mobilization from other plant organs. Evidence of independent re-mo bilization of carbohydrates and P towards the ear is presented, and th e pattern of plant development as well as the relationships between de velopment and dry matter and P allocation are discussed.