Integrated application of metal tolerant P. fluorescens and press mud for conferring heavy metal tolerance to aloe vera (Aloe barbadensis)

Soil pollution due to heavy metal (HM) contamination has emerged as a global issue worldwide owing to their adverse impacts on plant growth. Bioremediation approaches employing living organisms for HM alleviation have gained considerable attention among scientific community. Biological agents such as plant growth-promoting rhizobacteria (PGPR) offer a sustainable way to restore soil health, and their combination with different organic amendments such as press mud (PM) can serve as potential approach for immobilizing HMs in soil. We performed a pot experiment to evaluate the role of individual and combined application of press mud and PGPR strain 'FQ6' (identified as Pseudomonas fluorescens) in the phytoremediation of different HMs (Pb, Ni and Cd) and growth promotion of aloe vera. Combined application of FQ6 strain and PM yielded more significant outcomes in terms of all the growth and yield attributes such as leaf length (123 %), plant height (57 %), number of leaves (115 %), fresh and dry weights of gel (246 and 280 %), gel contents (96 %), root length (164 %), root diameter (220 %), no. of root tips (138 %) and root area (315 %), as compared to control. Combined application of FQ6 and PM also led to a significant improvement in different antioxidant activities i.e., CAT (129 %), SOD (48 %), APX (17 %) and POD (83 %) as compared to control. Contrastingly, mobility of these HMs was reduced under combined application of Pseudomonas strain 'FQ6' and PM, as there existed a considerable difference between HMs concentrations in soil and plant body. We concluded that joint application of HM-tolerant Pseu-domonas FQ6 strain and PM could be an ideal option to alleviate the HM induced adverse impacts on aloe vera by immobilizing them in soil, and subsequently, improving plant growth.