Endophytic bacterium Sphingomonas panaciterrae NB5 influences soil properties and improves growth, nutrient contents, and yield of red amaranth (Amaranthus tricolor L.)

Plant growth promoting rhizobacteria (PGPR) are crucial for enhancing plant growth and restoring soil health. Despite the excellent plant growth promoting traits, information is limited on the efficacy of Sphingomonas as a PGPR, especially in vegetable crops. In this study, we used Sphingomonas panaciterrae NB5 as a biofertilizer in leafy vegetable red amaranth in three methods: seed priming (SP), root drenching + foliar (RD + FA), and bacterial culture filtrate (BCF) foliar application. Bio-inoculation of NB5 significantly increased the plant height, number of leaves, leaf area, stem girth, total chlorophyll, vitamin C, and antioxidant contents of red amaranth in all methods of application. Bacterial treatment resulted in notable alterations to the root structure, consisting of the formation of secondary, tertiary, and fibrous roots, particularly in the BCF foliar application and RD + FA treatment.The fresh and dry biomass significantly increased both in root and shoot, resulting in improved yield. The nutritional profile revealed that bacterial application significantly increased the nitrogen, potassium, magnesium, iron, and zinc content, with a slight increase in phosphorus content, in shoots and roots in all the methods of bacterial application compared to control. In post-harvest soil, NB5 boosted total nitrogen, available phosphorus, calcium, and sulfur, as well as soil organic carbon (SOC) and total bacterial populations, regardless of the application methods. The RD+FA treatment outperformed the other methods of application in most of the plant and soil parameters, and the next was the BCF foliar application. Multivariate analysis also confirmed the better performance of RD+ FA and BCF foliar applications. Therefore, simultaneous application of NB5 through root drenching and foliar application could be recommended to the farmers for increasing the yield of red amaranth with improved nutrients and restoring soil health and productivity.