Genetic, physiological, and agronomic evaluation of adventitious rooting as a trait for phosphorus acquisition efficiency in common bean (Phaseolus vulgaris L.)

Adventitious rooting in common bean (Phaseolus vulgaris L.) is a genetically regulated process that may vary depending on the genotype and environmental signals such as soil phosphorus availability. In order to determine the genetic control, hormone regulation, and physiological mechanisms of adventitious rooting in common bean we conducted a series of field and greenhouse experiments under contrasting phosphorus availability, employing two contrasting landraces (G2333 and G19839) and 84 F5:8 recombinant inbred lines (RIL) derived from them. For the genetic studies we developed a new linkage map that allowed us to identified 20 new QTL for root characteristics related to low phosphorus adaptation. Identified QTL explained from 19% to 58% of the total phenotypic variation under field conditions. Two QTL for number of adventitious roots under low phosphorus in the field explained 61% of total phenotypic variation, while one QTL for this trait explained alone as much as 36% of observed phenotypic variation and had the highest LOD value of all the QTL detected (6.63).; Auxin and ethylene interacted to regulate adventitious root development. NAA (alpha-naphthalene acetic acid) increased adventitious root formation at the expense of basal root development. G2333 was significantly more responsive to a NAA than G19839. However, adventitious root formation in G19839 was more inhibited by an auxin transport inhibitor than G2333. Exogenous ethylene promoted adventitious rooting and was required for auxin-enhanced adventitious rooting and elongation.; Genotypes contrasting for adventitious rooting did not differ in phosphorus accumulation. This lack of difference was probably due to compensation between basal and adventitious roots. Basal roots represented more than 50% of the total root system and any decrease in basal root biomass could have strong effects on total phosphorus acquisition. Altering adventitious rooting with auxin in the RIL genotype that constitutively produces a low number of adventitious roots was important in determining that compensation among root classes occurred independent of the genetic background, seed size, or seed phosphorus reserve. These results will facilitate the use of adventitious rooting as a potential selection criterion for enhancing the adaptation of bean to low phosphorus soils.