applied sciences Article Efficacy of Indole Acetic Acid and Exopolysaccharides- Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.) Farheen Nazli 1 , Xiukang Wang 2, * , Maqshoof Ahmad 3, * , Azhar Hussain 3 , Bushra 3 , Abubakar Dar 3 , Muhammad Nasim 1 , Moazzam Jamil 3 , Nalun Panpluem 4 and Adnan Mustafa 5,6, *   Citation: Nazli, F.; Wang, X.; Ahmad, M.; Hussain, A.; Bushra; Dar, A.; Nasim, M.; Jamil, M.; Panpluem, N.; Mustafa, A. Efficacy of Indole Acetic Acid and Exopolysaccharides- Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.). Appl. Sci. 2021, 11, 4160. https://doi.org/ 10.3390/app11094160 Academic Editors: Federica Spina and Valeria Prigione Received: 18 March 2021 Accepted: 27 April 2021 Published: 2 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Pesticide Quality Control Laboratory, Government of the Punjab, Bahawalpur 63100, Pakistan; farheenmaqshoof@gmail.com (F.N.); mnasimshahid@yahoo.com (M.N.) 2 College of Life Sciences, Yan’an University, Yan’an 716000, China 3 Department of Soil Science, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan; azharhaseen@gmail.com (A.H.); bushra@iub.edu.pk (B.); abubakar.dar@iub.edu.pk (A.D.); moazzam.jamil@iub.edu.pk (M.J.) 4 School of Agriculture Cooperative and Agricultural Economics, Sukhothai Thamathirat Open University, Bangkok 11120, Thailand; pp.pilun@gmail.com 5 National Engineering Laboratory for Improving Quality of Arable Land, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China 6 Biology Centre CAS, SoWa RI, Na Sádkách 7, 37005 Cˇ eské Budˇ ejovice, Czech Republic * Correspondence: wangxiukang@yau.edu.cn (X.W.); maqshoof_ahmad@yahoo.com (M.A.); adnanmustafa780@gmail.com (A.M.) Abstract: Untreated wastewater used for irrigating crops is the major source of toxic heavy metals and other pollutants in soils. These heavy metals affect plant growth and deteriorate the quality of edible parts of growing plants. Phytohormone (IAA) and exopolysaccharides (EPS) producing plant growth-promoting rhizobacteria can reduce the toxicity of metals by stabilizing them in soil. The present experiment was conducted to evaluate the IAA and EPS-producing rhizobacterial strains for improving growth, physiology, and antioxidant activity of Brassica juncea (L.) under Cd-stress. Results showed that Cd-stress significantly decreased the growth and physiological parameters of mustard plants. Inoculation with Cd-tolerant, IAA and EPS-producing rhizobacterial strains, however, significantly retrieved the inhibitory effects of Cd-stress on mustard growth, and physiology by up regulating antioxidant enzyme activities. Higher Cd accumulation and proline content was observed in the roots and shoot tissues upon Cd-stress in mustard plants while reduced proline and Cd accumulation was recorded upon rhizobacterial strains inoculation. Maximum decrease in proline contents (12.4%) and Cd concentration in root (26.9%) and shoot (29%) in comparison to control plants was observed due to inoculation with Bacillus safensis strain FN13. The activity of antioxidant enzymes was increased due to Cd-stress; however, the inoculation with Cd-tolerant, IAA-producing rhizobacterial strains showed a non-significant impact in the case of the activity of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) in Brassica juncea (L.) plants under Cd-stress. Overall, Bacillus safensis strain FN13 was the most effective strain in improving the Brassica juncea (L.) growth and physiology under Cd-stress. It can be concluded, as the strain FN13 is a potential phytostabilizing biofertilizer for heavy metal contaminated soils, that it can be recommended to induce Cd-stress tolerance in crop plants. Keywords: metal toxicity; Bacillus; phytostabilization; exopolysaccharides; brassica; plant-microbe- interactions 1. Introduction The cultivated area in the world is decreasing due to urbanization and industrialization on fertile agricultural lands [1,2]. In the current scenario, increasing the cultivation area Appl. Sci. 2021, 11, 4160. https://doi.org/10.3390/app11094160 https://www.mdpi.com/journal/applsci