Speakers - AFHWC2025

Abstract

This research aimed to evaluate the biofertilizer potential of indigenous Rhizobium strains isolated from Adenocarpus boudyi, a wild leguminous shrub native to the High Atlas, to improve the productivity of Bituminaria bituminosa, a forage species of interest, and to contribute to the restoration and rehabilitation of degraded agro-sylvo-pastoral ecosystems in Morocco, which are particularly vulnerable to soil degradation and climate change.
Among the ten initial isolates tested, three strains Rhizobium pusense (R. pusense), Rhizobium radiobacter (R. radiobacter), and Rhizobium sp. demonstrated remarkable functional capacities. On solid NBRIP medium, phosphate solubilization indices ranged from 2.9 (Rhizobium sp.) to 3.9 (R. pusense), while in liquid medium, R. pusense solubilized the highest amount of phosphorus (118.34 µg/mL), followed by 111.35 µg/mL and 109.40 µg/mL for the other strains. A progressive acidification of the culture medium was observed, with pH decreasing to as low as 2.88 in R. radiobacter cultures.
All three strains produced indole-3-acetic acid, with maximum concentrations of 151.2 µg/mL R. pusense, 141.2 µg/mL R. radiobacter, and 46.4 µg/mL Rhizobium sp. Siderophore production was confirmed qualitatively for all isolates on Chrome Azurol S medium. Genotypic characterization revealed 100% similarity of isolate 36 to R. pusense, 99.72% similarity of isolate 39 to R. radiobacter, and 94% similarity of isolate 27 to Rhizobium sp.
In inoculation trials on B. bituminosa, clear differences in infectivity and effectiveness were observed. R. pusense formed an average of more than 25 nodules per plant, with a fresh nodule weight of 0.5 g, significantly outperforming R. radiobacter, which formed only 2.4 nodules with a weight of 0.028 g. Rhizobium sp. did not induce any nodulation. Statistical analyses confirmed highly significant differences between treatments (p<0.05).
Inoculation also significantly enhanced plant growth. Fresh shoot biomass increased by 12.2 g (+448%) with R. pusense, 10.51 g with R. radiobacter, and 9.1 g with Rhizobium sp., compared to uninoculated controls. Dry shoot biomass gains were also notable (5.51 g with R. pusense), as were improvements in root dry weight, which was highest with R. pusense and Rhizobium sp. The nitrogen content of aerial parts reached 0.082 g/plant in R. pusense inoculated plants, with 98% of nitrogen derived from atmospheric fixation, versus 0.015 g and 86% fixation for R. radiobacter.
Overall, the efficiency, expressed as the percentage increase in dry biomass relative to controls, ranged from 319% R. radiobacter to 448% R. pusense. A strong correlation was observed between the number of nodules and plant productivity, underscoring the superior infectivity and effectiveness of R. pusense.
These results demonstrate that the combined capacity of these locally adapted rhizobia to fix nitrogen, solubilize phosphorus, and produce phytohormones and siderophores represents a comprehensive biotechnological tool to sustainably improve the productivity of agro-sylvo-pastoral systems and restore degraded soils. The outstanding performance of R. pusense suggests that this strain should be further developed as a specific inoculant for forage crops in arid and semi-arid agro-sylvo-pastoral areas. Field studies will be essential to confirm these promising results and to establish large-scale application protocols to support sustainable, resilient, and ecosystem-restorative agriculture in Morocco.
Keywords: Agricultural science, phosphate solubilization, nitrogen fixation, biofertilizer, Biorestoration