Effect of chlorimuron‐ethyl on Bradyrhizobium japonicum and its symbiosis with soybean

Abstract

Possible side-effects of the acetolactate synthase (ALS)-inhibiting herbicide chlorimuron-ethyl on Bradyrhizobium japonicum (Kirchner & Jordan) in pure culture and on inoculated soybean plants growing under controlled conditions were investigated. Growth of B japonicum strain E109 was not affected by this herbicide even when exposed to concentrations 150 times higher than recommended field doses. However, nodulation of soybean plants treated 5 days after emergence with chlorimuron-ethyl at standard application rates was impaired: a 38% decrease in the number of nodules per plant was observed four weeks after treatment. Despite nodule number decrease, no changes in shoot nitrogen content could be detected. Total fresh biomass was diminished by 25% in herbicide-treated plants. Leghemoglobin content in nodules did not vary; nevertheless total nodule protein was diminished by 40% in the herbicide-treated group. ALS activity in different soybean tissues and their relative sensitivity to chlorimuron-ethyl were also investigated. Roots and bacteroids had the greatest specific ALS activities. On a fresh weight basis, the bacteroid fraction displayed the highest ALS activity and was also the most tolerant to in vitro chlorimuron addition: 72% of its activity was retained after including 10 microM chlorimuron-ethyl in the reaction mixture. These results indicate that standard application rates of chlorimuron-ethyl will have limited incidence on B japonicum survival, and effects on nodulation may have little long-term consequences on soybean nitrogen fixation potential. The differences found among soybean tissues not only in intrinsic ALS activity but also in their relative sensitivity to this herbicide suggests that, in leguminous plants living in symbiosis with rhizobia, nodules may contribute to an enhanced tolerance to ALS inhibitors.

Small RNAs of theBradyrhizobium/Rhodopseudomonaslineage and their analysis

“…34 Likewise, the decrease in the amount of BjrC1505 during symbiosis is in line with the expression of its putative target, acetolactate synthase (blr4023) in bacteroids. 34,45 Furthermore, the suggestion that BjrC2a paralogs act as antisense RNAs regulating inositol monophosphatase in Rhizobiales fits well to the reported need for a fine tuning the synthesis of this protein in Rhizobium leguminosarum for successful symbiosis with plants. 46,47 Since genomes of non-symbiotic Rhodopseudomonas and symbiotic Bradyrhizobium species were used for the prediction of sRNAs, many sRNAs with increased expression in bacteroids are probably not exclusively involved in the interaction between B. japonicum and its host plant, but may contribute to other, more general aspects of bacteroid physiology.…”

Toxicity Assessment of Herbicides Quizalafop-p-Ethyl and Clodinafop Towards Rhizobium Pea Symbiosis

“…For example, sethoxydim, alachlor, fluazifop butyl and metolachlor at recommended rates did not result in detrimental effects on seed yields or N 2 fixation in soybean while paraquat significantly reduced the amount of N 2 fixed as measured by 15 N dilution methods (Kucey et al 1988). Similarly, the adverse effects of terbutryn/terbuthylazine and bentazone on the performance of pea (Singh and Wright 2002b) and the phytotoxic effects of chlorimuron-ethyl on Bradyrhizobium japonicum inoculated soybean (Zawoznik and Tomaro 2005) is reported. Plant growth promoting rhizobacteria including symbiotic N 2 fixers can affect plant development either indirectly by circumventing the toxic effects of pesticides (Yang and Lee 2008) or directly by synthesizing the plant growth regulating substances (Wani et al 2008).…”

Characterization of soybean population with sulfonylurea herbicides tolerant alleles

“…Having proof the soybean capacity to tolerate some active ingredients of sulfonylureas, such as ethyl chlorimuron, through its fast metabolic inactivation, this active ingredient has become widely used in soybean crops (Zawoznik and Tomaro, 2005). Currently, in Brazil, chlorimuron ethyl is used during pre and post-emergence for the control mainly of weeds resistant to glyphosate.…”