Selection of common bean (Phaseolus vulgaris L.) for N2 fixation at different levels of available phosphorus under field and environmentally-controlled conditions

Phosphorus is one of several factors which affect N₂ fixation and along with N, is a principal yield-limiting nutrient in many regions of the world. Since the legume plant is an essential partner in symbiotic N₂ fixation, knowledge of host genotype variability for this process at different levels of P availability will be useful when breeding bean cultivars for enhanced N₂ fixation. The objective of this study was to obtain common bean (Phaseolus vulgaris L.) lines able with enhanced ability to support biological N₂ fixation under different levels of available phosphorus.Experiments were conducted in a growth room using a sand-alumina system to provide different levels of available P and in the field on a low-N soil. In the growth room studies, P availability strongly affected plant growth and traits related to N₂ fixation. No significant interaction was detected for P levels × bean lines, indicating that bean lines performed similarly at both high and low P levels.Total shoot N was used as a direct and indirect measure of N₂-fixation potential under growth room (N-free media) and field (low-N soil) conditions, respectively. Based on this criterion, two of the 41 and 54 inbred backcross lines of a segregating population evaluated in the growth room and the field, respectively, contained greater shoot N content than the recurrent parent and N shoot contents similar to the donor parent. Variability of N₂ fixation under low available P was observed, and high N₂ fixing and high yielding progeny lines were detected.