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 growth 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 after 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% FC by weighing and watering the pots every two to three days. Shoots were harvested four times before anthesis and twice after. At each harvest, 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 allocation 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 of soil. In this study, the final composition of the grain depended on re-mobilization from other plant organs. Evidence of independent re-mobilization of carbohydrates and P towards the ear is presented, and the pattern of plant development as well as the relationships between development and dry matter and P allocation are discussed.