Variability in plant-microbe interaction between Lupinus lines and Bradyrhizobium strains

Even though lupin (Lupinus albus L.) is known to potentially fix 150-200 kg/ha nitrogen for the use of a succeeding crop, precise information about lupinxBradyrhizobium strain interaction under the climatic conditions prevalent in the mid-Atlantic region of the United States is unknown. We conducted two greenhouse experiments with the objective of characterizing this symbiotic relationship and to evaluate potential interaction between Bradyrhizobium strains and lupin lines. In the first experiment, performance of 60 bradyrhizobial strains was evaluated by inoculating three lupin cultivars and using combined score, which consisted of an arithmetic total of plant vigor, nodulation scores from crown root, nodulation scores from fibrous roots, shoot dry weight, and root dry weight. In the second experiment, performance of 80 lupin lines was evaluated by inoculating with three selected Bradyrhizobial strains and using the combined score, which consisted of an arithmetic total of plant vigor, acetylene reduction activity, nodule number per plant, nodule weight per plant, and dry shoot weight. Significant variation existed for all traits in both experiments except for nodule number in the second experiment. Significant Bradyrhizobial strain by lupin line interaction existed for nodulation score, shoot and root dry weights, and the combined scores. Comparison of relative ranks indicated that nodulation effectiveness was dependent on specific strain and lupin line combinations. It was concluded that specific Bradyrhizobial strain and lupin line combinations would need to be identified for successful utilization of lupin's capability to fix atmospheric nitrogen for use in low-input and sustainable agriculture.