article · Plants
Argania spinosa is an ecologically and socio-economically important tree facing habitat degradation. Harnessing plant growth-promoting rhizobacteria from its soil could support reforestation and soil enrichment. Researchers isolated 120 bacteria from the argan rhizosphere, screening them for phosphate solubilisation and indole acetic acid production. Fifty-two isolates solubilised phosphorus, and twenty-five of those produced indole acetic acid. Following pre-screening on maize growth, eight high-performing isolates were identified through sequencing, representing species of Brevundimonas naejangsanensis, Alcaligenes faecalis, Leucobacter aridicollis, and Staphylococcus saprophyticus. These isolates significantly boosted argan seed germination, radicle extension, and greenhouse growth metrics. In particular, Leucobacter aridicollis sp2 raised germination to 95.83 percent, whilst Leucobacter aridicollis sp1 and Brevundimonas naejangsanensis sp3 substantially increased seedling height, collar diameter, and branch count.
Argan forests are essential for local livelihoods and environmental stability but suffer from degradation and regeneration bottlenecks. Using beneficial native soil bacteria provides a sustainable method to accelerate seed germination and nursery seedling development. This biological approach strengthens reforestation programmes, improves soil nutrient availability, and aids in the preservation of fragile arid ecosystems.
This research provides applied and tested data from laboratory and greenhouse trials. It could enable the formulation of microbial biofertilisers and seed treatments for forestry nurseries, reforestation initiatives, and sustainable agriculture operations. Commercial translation would require moving from controlled greenhouse settings to field-scale trials, establishing scalable bacterial culturing methods, and securing regulatory approval for bio-inoculants in forest management.
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<i>Argania spinosa</i> is among the most important species of the Moroccan forest in terms of ecological, environmental, and socio-economic aspects. However, it faces a delicate balance between regeneration and degradation in its natural habitat. Hence, the efforts to preserve and regenerate argan forests are crucial for biodiversity, soil quality, and local livelihoods, yet they face challenges like overgrazing and climate change. Sustainable management practices, including reforestation and community engagement, are vital for mitigating degradation. Similarly, exploiting the argan tree's rhizosphere can enhance soil quality by leveraging its rich microbial diversity. This approach not only improves crop growth but also maintains ecosystem balance, ultimately benefiting both agriculture and the environment. This enrichment can be achieved by different factors: mycorrhizae, plant extracts, algae extracts, and plant growth-promoting rhizobacteria (PGPR). The benefits provided by PGPR may include increased nutrient availability, phytohormone production, shoot, root development, protection against several plant pathogens, and disease reduction. In this study, the effect of rhizobacteria isolated from the Agran rhizosphere was evaluated on germination percentage and radicle length for <i>Argania spinosa</i> in vitro tests, growth, collar diameter, and branching number under greenhouse conditions. One hundred and twenty (120) bacteria were isolated from the argan rhizosphere and evaluated for their capacity for phosphate solubilization and indole acetic acid production. The results showed that 52 isolates could solubilize phosphorus, with the diameters of the solubilization halos varying from 0.56 ± 0.14 to 2.9 ± 0.08 cm. Among 52 isolates, 25 were found to be positive for indole acetic acid production. These 25 isolates were first tested on maize growth to select the most performant ones. The results showed that 14 isolates from 25 tested stimulated maize growth significantly, and 3 of them by 28% (CN005, CN006, and CN009) compared to the control. Eight isolates (CN005, CN006, CN004, CN007, CN008, CN009, CN010, and CN011) that showed plant growth of more than 19% were selected to evaluate their effect on argan germination rate and radicle length and were subjected to DNA extraction and conventional Sanger sequencing. The 8 selected isolates were identified as: <i>Brevundimonas naejangsanensis</i> sp2, <i>Alcaligenes faecalis</i>, <i>Brevundimonas naejangsanensis</i> sp3, <i>Brevundimonas naejangsanensis</i> sp4, <i>Leucobacter aridicollis</i> sp1, <i>Leucobacter aridicollis</i> sp2, <i>Brevundimonas naejangsanensis</i> sp1, and <i>Staphylococcus saprophyticus</i>. The results showed that <i>Leucobacter aridicollis</i> sp2 significantly increased the germination rate by 95.83%, and the radicle length with a value of 2.71 cm compared to the control (1.60 cm), followed by <i>Brevundimonas naejangsanensis</i> sp3 and <i>Leucobacter aridicollis</i> sp1 (2.42 cm and 2.11 cm, respectively). Under greenhouse conditions, the results showed that the height growth increased significantly for <i>Leucobacter aridicollis</i> sp1 (42.07%) and <i>Leucobacter aridicollis</i> sp2 (39.99%). The isolates <i>Brevundimonas naejangsanensis</i> sp3 and <i>Leucobacter aridicollis</i> sp1 increased the gain of collar diameter by 41.56 and 41.21%, respectively, followed by <i>Leucobacter aridicollis</i> sp2 and <i>Staphyloccocus saprophyticus</i> (38.68 and 22.79%). <i>Leucobacter aridicollis</i> sp1 increased the ramification number per plant to 12 compared to the control, which had 6 ramifications per plant. The use of these isolates represents a viable alternative in sustainable agriculture by improving the germination rate and root development of the argan tree, as well as its development, while increasing the availability of nutrients in the soil and consequently improving fertilization.
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DOI: 10.3390/plants13152025
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