Integration of P acquisition efficiency, P utilization efficiency and low grain P concentrations into P-efficient rice genotypes for specific target environments

Poor yields in low-input farms and high fertilizer and environmental costs in high-input farms call for more efficient use of phosphorus (P) in rice systems. One approach to increasing the P efficiency (PE) of cropping systems is to develop P-efficient genotypes. Two key traits have been thought to contribute to genotypic PE, namely the efficiency at which P is taken up (PAE) and at which P taken up is converted to biomass (PUE). Low grain P concentration (LGP) has recently been proposed as a third key trait that could improve the PE of a system through reduced P removal with grains. Screening methods for PAE, PUE and LGP are discussed with particular focus on interactions among these traits and the potential to exploit genotypic variation for breeding P-efficient rice genotypes targeted to specific environments. Further, potential changes in nutrient budgets within the known scope of genotypic variation for key PE traits in rice were evaluated. At low to medium yield, simulated yield increased with 40-60 and 15 % by increasing PAE and PUE respectively. Higher PAE increased P removal with 1-2 kg P ha(-1) at low to medium yields, leading to accelerated P mining when no P is applied. Limited scope exists for reducing P mining by a LGP trait in severely P-deficient systems, but P removal from fields can be reduced with 0.5-5 kg P ha(-1) by a LGP trait at medium to high yields. Maximal gains in efficiency can be achieved by integrating key traits into P-efficient genotypes.