Utility of Dimorphic Root Systems for Tolerance to Combined Drought and Low Phosphorus in Common Bean (Phaseolus vulgaris).

Drought and low phosphorus are primary limitations to bean production worldwide and often occur simultaneously.  Under terminal drought conditions, water is generally available deep in the soil profile whereas phosphorus is generally available in superficial layers. Shallow root systems have been shown to be beneficial for low P soil and deep root systems for drought conditions. Breeders need information about root traits that enable efficient acquisition of both phosphorus and water.  We hypothesize that root systems with architectural traits that facilitate efficient exploration and acquisition of resources from both deep and shallow soil layers, i.e. dimorphic root systems, will be more tolerant to combined drought and low phosphorus.

Recombinant inbred lines contrasting for root architectural traits were selected from the L88 and DOR364 x BAT477 populations, as well as from crosses between Amadeus and L88 lines.  Field experiments were conducted in Alma, South Africa 2011 and 2012, Sussendenga, Mozambique 2012, and Rock Springs Research Farm, Pennsylvania 2011 and 2012.  Laboratory experiments were conducted in University Park, Pennsylvania 2012.   Lines with dimorphic root systems showed greater biomass, leaf area, leaf CO₂ assimilation, and stomatal conductance, and less negative stem water potential than either deep or shallow phenotypes under combined stress.  We conclude that dimorphic phenotypes are an effective strategy for productivity in combined phosphorus and water limited environments.