Table_5_Effects of Nitrogen Application on Nitrogen Fixation in Common Bean Production.docx

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.

本研究旨在降低普通菜豆（Phaseolus vulgaris L.）生产中氮肥的使用量。相较于其他豆科植物，普通菜豆与根瘤菌的固氮能力通常被认为较弱，因此豆类生产中普遍使用氮肥以实现高产，这在一般情况下会抑制固氮作用。此外，植物无法吸收施加于土壤中的所有氮肥，导致径流和地下水污染。本研究的总体目标是减少普通菜豆生产中氮肥的使用。这将极大推动加拿大普通菜豆产业的盈利能力，并显著改善作物的生态足迹。在当前的研究中，对22个豆类基因型（包括来自Mist × Sanilac群体的重组自交系（RILs）以及一个非结瘤突变体（R99））进行了筛选，以评估其在四种氮肥管理下的大气氮固定能力。这些基因型在三年内于贫氮土壤上进行的重复田间试验中，对大气氮来源百分比（%Ndfa）、产量以及多个与产量相关的性状进行了评估。豆类基因型在所有分析性状上均存在差异，氮水平显著影响大多数性状，包括在三年中的%Ndfa和产量。相比之下，根瘤菌的应用仅对少数性状产生显著影响，且其影响在年度间不一致。氮肥施用在不同豆类基因型中降低了共生固氮（SNF）的程度。这种变异表明，通过育种和选择能够在降低肥料水平下固定氮的豆类基因型能力，可以改善普通菜豆的SNF。此外，如RIL_38、RIL_119和RIL_131等基因型，既高产又良好的固氮能力，具有同时提高这两项性状的潜力。然而，由于这些性状之间缺乏一致性关联，育种进展可能较为缓慢。