Exploring the synergistic effects of indole acetic acid (IAA) and compost in the phytostabilization of nickel (Ni) in cauliflower rhizosphere.

Heavy metals (HMs) contamination, owing to their potential links to various chronic diseases, poses a global threat to agriculture, environment, and human health. Nickel (Ni) is an essential element however, at higher concentration, it is highly phytotoxic, and affects major plant functions. Beneficial roles of plant growth regulators (PGRs) and organic amendments in mitigating the adverse impacts of HM on plant growth has gained the attention of scientific community worldwide. Here, we performed a greenhouse study to investigate the effect of indole-3-acetic acid (IAA @ 10- 5 M) and compost (1% w/w) individually and in combination in sustaining cauliflower growth and yield under Ni stress. In our results, combined application proved significantly better than individual applications in alleviating the adverse effects of Ni on cauliflower as it increased various plant attributes such as plant height (49%), root length (76%), curd height and diameter (68 and 134%), leaf area (75%), transpiration rate (36%), stomatal conductance (104%), water use efficiency (143%), flavonoid and phenolic contents (212 and 133%), soluble sugars and protein contents (202 and 199%), SPAD value (78%), chlorophyll 'a and b' (219 and 208%), carotenoid (335%), and NPK uptake (191, 79 and 92%) as compared to the control. Co-application of IAA and compost reduced Ni-induced electrolyte leakage (64%) and improved the antioxidant activities, including APX (55%), CAT (30%), SOD (43%), POD (55%), while reducing MDA and H2O2 contents (77 and 52%) compared to the control. The combined application also reduced Ni uptake in roots, shoots, and curd by 51, 78 and 72% respectively along with an increased relative production index (78%) as compared to the control. Hence, synergistic application of IAA and compost can mitigate Ni induced adverse impacts on cauliflower growth by immobilizing it in the soil.

Comparative efficacy of different salt tolerant rhizobial inoculants in improving growth and productivity of Vigna radiata L. under salt stress.

Worldwide, salinity severely affects agricultural production of crops such as mung bean in arid and semi-arid regions. In saline conditions, various species of Rhizobium can be used to enhance nodulation and induce salinity tolerance in maize. The present study conducted a pot experiment to determine the efficiency of three rhizobial isolates under different salinity conditions, such as 1.41, 4 and 6 dS m-1, on mung bean growth parameters, antioxidant status and yield. Results revealed that salt stress imparted adverse effects on the growth, antioxidants, yield and nodulation of mung bean. Under high salt stress conditions, fresh weights were reduced for roots (78.24%), shoots (64.52%), pods (58.26%) and height (32.33%) as compared to un-inoculated control plants. However, an increase in proline content (46.14%) was observed in high salt stressed plants. Three Rhizobium isolates (Mg1, Mg2, and Mg3), on the other hand, mitigated the negative effects of salt stress after inoculation. However, effects of Mg3 inoculation were prominent at 6 dS m-1 and it enhanced the plant height (45.10%), fresh weight of shoot (58.68%), root (63.64%), pods fresh weight (34.10%), pods number per plant (92.04%), and grain nitrogen concentration (21%) than un-inoculated control. Rhizobium strains Mg1, and Mg2 expressed splendid results at 1.41 and 4 dS m-1 salinity stress. The growth promotion effects might be due to improvement in mineral uptake and ionic balance that minimized the inhibitory effects caused by salinity stress. Thus, inoculating with these strains may boost mung bean growth and yield under salinity stress.

Co-application of organic amendments and Cd-tolerant rhizobacteria for suppression of cadmium uptake and regulation of antioxidants in tomato.

Cadmium (Cd) contamination is a major environmental concern with well-reported adverse impacts on environment and living entities. It limits the productivity of agricultural crops due to its excessive entry to plant tissues, and subsequent toxic effects on their growth and physiology. Application of metal tolerant rhizobacteria in combination with organic amendments has shown beneficial impacts in sustaining plant growth, on account of amendments mediated decreased metal mobility via different functional groups, as well as provision of carbon to microorganisms. We evaluated the effect of organic amendments (compost and biochar) and Cd-tolerant rhizobacteria on growth, physiology, and Cd uptake in tomato (Solanum lycopersicum). Plants were grown under Cd contamination (2 mg kg-1), and were supplemented with 0.5% w/w of compost and biochar along with rhizobacterial inoculation in pot culture. We observed a significant reduction in shoot length, fresh and dry biomass (37, 49 and 31%) and root attributes such as root length, fresh and dry weights (35, 38 and 43%). However, Cd tolerant PGPR strain 'J-62' along with compost and biochar (0.5% w/w) mitigated the Cd induced adverse impacts on different plant attributes and improved these attributes such as root and shoot lengths (112 and 72%), fresh (130 and 146%) and dry weights (119 and 162%) of tomato roots and shoots as compared to relative control treatment. Furthermore, we observed significant increments in different antioxidant activities such as SOD (54%), CAT (49%) and APX (50%) under Cd contamination. Combined application of 'J-62' strain and organic amendments also decreased Cd translocation towards different above-ground plant parts as was pragmatic in terms of bioconcentration and translocation factors of Cd, which indicated phyto-stabilization ability of our inoculated strain for Cd. Hence, Cd tolerant PGPR in combination with organic amendments can immobilize Cd in soil and thereby, can alleviate Cd induced adverse impacts on tomato growth.