Variability of Phosphorus Uptake and Translocation in Phaseolus vulgaris L. under Phosphorus Stress1

Excised roots were used for evaluating methods and in identifying differences in rates of P absorption by 59 lines of Phaseolus vulgaris . Large variations in P absorption rates between lines were noted. Although the P absorption rate was negatively correlated with root dry weight, it was possible to isolate lines with similar excised root dry weights which displayed large differences in P absorption rates. Rates of P absorption by the terminal 3.5 cm root segment satisfactorily expressed P absorption by other portions of the root system. The rate of P absorption by excised roots was influenced by the amount of P in the solution in which plants were cultured prior to root excision. As the pretreatment P level increased from 3 to 31 mg/plant, P absorption by excised roots decreased and as the P level increased from 31 to 62 mg/plant, P absorption by excised roots leveled off. Rates of P absorption by excised roots also varied with the age of the plant. However, relative values between efficient and inefficient lines remained constant at each plant age. Variance for P absorption by excised roots due to environment was high. Narrow sense heritability estimates derived from parent offspring regression in families of efficient × inefficient lines were estimated to be about 40%. Data on P uptake by excised roots did not predict P uptake and translocation in intact plants. A reliable standardized technique for intact plant ion absorption studies is necessary to make accurate comparisons between plants.