Lack of evidence for programmed root senescence in common bean (Phaseolus vulgaris) grown at different levels of phosphorus supply

The influence of phosphorus (P) availability on root lifespan in common bean (Phaseolus vulgaris cv. Carioca) is reported here, as well as patterns of root survivorship in relation to vegetative and reproductive development. Plants were grown in a glasshouse in a sand-culture system with varying P availability, and in a high-P field soil with greater biotic activity. Root dynamics were assessed using a minirhizotron system. Phosphorus limitation, which reduced plant growth by 90%, did not diminish root survivorship. At nonlimiting and limiting R root survivorship was not synchronized closely with shoot development and senescence; a substantial portion of the roots were present and seemingly alive even beyond reproductive maturity. In field-grown beans and in beans under severe P limitation in sand culture, survivorship fell approx. 50%, but only after pod fill was nearly complete. Common bean does not exhibit programmed root senescence during and immediately following pod fill. Roots died after the shoot had undergone other senescence processes, such as leaf drop and pod dry-down. Under field conditions, soil organisms are likely to modulate the effects of phosphorus deficiency and pod fill on root death.