Abstract
The nitrogen fixing ability of common bean (Phaseolus vulgaris L.) in association with rhizobia is often characterized as poor compared to other legumes, and nitrogen fertilizers are commonly used in bean production to achieve high yields, which in general inhibits nitrogen fixation. In addition, plants cannot take up all the nitrogen applied to the soil as a fertilizer leading to runoff and groundwater contamination. The overall objective of this work is to reduce use of nitrogen fertilizer in common bean production. This would be a major advance in profitability for the common bean industry in Canada and would significantly improve the ecological footprint of the crop. In the current work, 22 bean genotypes [including recombinant inbred lines (RILs) from the Mist × Sanilac population and a non-nodulating mutant (R99)] were screened for their capacity to fix atmospheric nitrogen under four nitrogen regimes. The genotypes were evaluated in replicated field trials on N-poor soils over three years for the percent nitrogen derived from atmosphere (%Ndfa), yield, and a number of yield-related traits. Bean genotypes differed for all analyzed traits, and the level of nitrogen significantly affected most of the traits, including %Ndfa and yield in all three years. In contrast, application of rhizobia significantly affected only few traits, and the effect was inconsistent among the years. Nitrogen application reduced symbiotic nitrogen fixation (SNF) to various degrees in different bean genotypes. This variation suggests that SNF in common bean can be improved through breeding and selection for the ability of bean genotypes to fix nitrogen in the presence of reduced fertilizer levels. Moreover, genotypes like RIL_38, RIL_119, and RIL_131, being both high yielding and good nitrogen fixers, have potential for simultaneous improvement of both traits. However, breeding advancement might be slow due to an inconsistent correlation between these traits.
Highlights
Common bean (Phaseolus vulgaris L.) is the most important legume crop used for direct human consumption
The selection of recombinant inbred lines (RILs) was based on the SNF relative efficiency index (SNFI) index (Farid, 2015) and included 10 symbiotic nitrogen fixation (SNF)-dependent RILs [high yield under SNF condition (RIL_16, RIL_38, RIL_46, RIL_76, RIL_89, RIL_102, RIL_104, RIL_119, RIL_122 and RIL_136)] and seven N-dependent RILs [high yield under nitrogen application (RIL_3, RIL_24, RIL_25, RIL_70, RIL103, RIL_113 and RIL_131)]
The current study identified a few high yielding genotypes with good nitrogen fixing capabilities
Summary
Common (dry) bean (Phaseolus vulgaris L.) is the most important legume crop used for direct human consumption. Biological (symbiotic) nitrogen fixation (BNF, SNF) is a sustainable and economical alternative for supplying nitrogen to legume crops, including common bean and soybean (Thilakarathna and Raizada, 2018). It can reduce crop input costs by eliminating the need to purchase nitrogen fertilizer and reduce the negative impacts of unused nitrogen in the environment (Stevens et al, 2004; Good and Beatty, 2011; Khan et al, 2020)
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