Development and characterization of efficient k-solubilizing rhizobacteria and mesorhizobial inoculants for chickpea

The use of mineral fertilizers has long been associated with the improved growth of crop plants as well as increased yield potential per unit area. However, the incessant practice of imbalanced fertilizers application has increased the economic and environmental costs for the agricultural sector. The deficiency of potassium (K) has been identified as a primary crop production challenge in certain semi-arid regions where soil-K reserves are increasingly being depleted. This study aimed to isolate and characterize K-solubilizing bacterial strains from the rhizosphere and root nodules of chickpea. Initially, 50 rhizobacterial strains and 50 rhizobial strains were isolated using Aleksandrov’s medium. Each of these collections was narrowed down to 25 strains, following a rigorous qualitative screening based on different physiological, morphological and biochemical tests. From these, five strains each of rhizosphere and nodule origins were selected based on qualitative as well quantitative determination of various growth promoting traits. In addition to efficient potassium and phosphate solubilization, the selected strains displayed better growth conditions, as evident by glucose substrate use at 25◦C and pH 7. In this study, we found that strains SKB3 (rhizosphere) and JKR7 (rhizobia) were the most efficient K-solubilizers. Additionally, they possessed diverse plant growth promoting traits such as root colonization, the synthesis of siderophores, exopolysaccharides, chitinase activity, indole-acetic acid production and 1-aminocyclopropane-1-carboxylic acid deaminase activity. Overall, our results suggest that the application of bacterial K-solubilizers could be employed as a useful K-supplement in K-limited agroecosystems. Moreover, the use of these K-solubilizers may help lead in alleviating the negative environmental impacts associated with chemical fertilizer.I am very grateful to all of those with whom I have had the pleasure to work during this project, especially the Department of Soil and Environmental Sciences, College of Agriculture, University of Sargodha, Sargodha, Pakistan, the Soil & Water Sciences Department (SWD), Institute of Food and Agricultural Sciences (IFAS), University of Florida, USA, and the Higher Education Commission (HEC), Islamabad, Pakistan. Each of the members of the SWD, IFAS, University of Florida, USA, specifically L.Q. Ma, Letuzia Maria De Oliveira and Evandro Da Silva have provided me with extensive personal and professional guidance and have taught me a great deal about both scientific research and life in general during my six months stay there under International Research Support Initiative Program (IRSIP), HEC, Pakistan. The authors would also like to extend their sincere appreciation to the acknowledgment of the research supporting project (RSP-2021/95, King Saud University, Riyadh, Saudi Arabia)