Soybean [Glycine max (L.) Merr.] has great economic and nutritional importance mainly due to its high protein content. All plant's N needs can be met by the symbiosis with elite Bradyrhizobium strains applied as inoculants to the seeds at sowing time; however, the increasing use of pesticides in seed treatments can impair the contribution of the biological nitrogen fixation. In this study, we report decreases in cell survival of two strains, B. japonicum SEMIA 5079 and B. elkanii SEMIA 587 in seeds inoculated and treated with StandakTop™, composed of the fungicides pyraclostrobin and thiophanate-methyl and the insecticide fipronil, the pesticides most used in soybean seed treatment in several countries. Cell death was enhanced with the time of exposure to the pesticides, and B. elkanii was less tolerant, with almost no detectable viable cells after 15 days. Change in colony morphology with smaller colonies was observed in the presence of the pesticides, being more drastic with the time of exposure, and attributed to an adaptive response towards survival in the presence of the abiotic stress. However, morphological changes were reversible after elimination of the stressing agent and symbiotic performance under controlled greenhouse conditions was similar between strains that had been or not exposed to the pesticides. In addition, no changes in DNA profiles (BOX-PCR) of both strains were observed after the contact with the pesticides. In two field experiments, impacting effects of the pesticides were observed mainly on the total N accumulated in grains of plants relying on both N2-fixation and N-fertilizer. Our data indicate that StandakTop® affects parameters never reported before, including colony morphology of Bradyrhizobium spp. and N metabolism and/or N remobilization to soybean grains.

中文翻译：

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农药对慢生根瘤菌特性的影响。以及与大豆的共生表现


大豆 [Glycine max (L.) Merr.] 因其高蛋白质含量而具有巨大的经济和营养价值。所有植物的氮需求都可以通过与优良慢生根瘤菌菌株的共生来满足，在播种时将其用作种子的接种剂；然而，在种子处理中越来越多地使用农药可能会削弱生物固氮的作用。在这项研究中，我们报告了两种菌株（B. japonicum SEMIA 5079 和 B. elkanii SEMIA 587）在用 StandakTop™（由杀菌剂唑菌胺酯和甲基托布津以及杀虫剂氟虫腈组成）接种和处理的种子中的细胞存活率下降。在一些国家，主要用于大豆种子处理。细胞死亡随着接触农药时间的延长而增强，而艾氏芽孢杆菌的耐受性较差，15 天后几乎检测不到活细胞。在存在农药的情况下观察到菌落形态的变化，菌落较小，随着接触时间的延长，菌落形态的变化更加剧烈，这归因于在非生物胁迫存在下对生存的适应性反应。然而，在消除应激剂后，形态变化是可逆的，并且在受控温室条件下，已接触或未接触农药的菌株之间的共生性能相似。此外，在接触农药后，两种菌株的 DNA 谱 (BOX-PCR) 均未观察到变化。在两次田间试验中，观察到农药对依靠固氮和施氮肥的植物籽粒中积累的总氮的影响。我们的数据表明，StandakTop® 会影响以前从未报道过的参数，包括慢生根瘤菌 (Bradyrhizobium spp) 的菌落形态。 氮代谢和/或氮再动员至大豆籽粒。