Table_8_Effects of Nitrogen Application on Nitrogen Fixation in Common Bean Production.xlsx

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.

豆科植物中，菜豆（Phaseolus vulgaris L.）与根瘤菌的共生固氮能力常被描述为相较于其他豆科植物较为低下，因此在豆类生产中普遍采用氮肥以实现高产，而这通常会对固氮作用产生抑制作用。此外，植物无法吸收土壤中作为肥料施加的所有氮，导致径流和地下水污染。本研究的总体目标是减少菜豆生产中氮肥的使用。这将极大地提升加拿大菜豆产业的盈利能力，并显著改善作物的生态足迹。在当前研究中，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方式下固定大气氮的能力。这些基因型在三年内重复进行的田间试验中，在贫氮土壤上进行了评价，评估内容包括从大气中获得的氮百分比（%Ndfa）、产量以及多个与产量相关的性状。豆类基因型在所有分析的性状上均存在差异，氮水平对大多数性状（包括三年内的%Ndfa和产量）均有显著影响。相比之下，根瘤菌的应用仅对少数性状产生了显著影响，且在不同年份间的影响不一致。氮肥的应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，通过育种和选择在降低肥料水平下具有固氮能力的豆类基因型，可以改善菜豆的固氮作用。此外，如RIL_38、RIL_119和RIL_131等基因型，既具有较高的产量，又是良好的固氮者，具有同时改善这两个性状的潜力。然而，由于这些性状之间的关联性不稳定，育种进展可能较为缓慢。