Abstract
Calicotome villosa is a spontaneous Mediterranean legume that can be a good candidate as pioneer plants to limit regression of vegetation cover and loss of biodiversity in Tunisian arid soils. In order to grow legumes in such soils, pairing rhizobia and nodule associated bacteria (NAB) might provide numerous advantages. In this work, cultivable biodiversity of rhizobial symbionts and NAB in nodules of C. villosa plants growing in five arid regions of south Tunisia was characterized. Phylogenetic analysis using 16S rDNA gene, dnak, recA and nodD sequences separated nodule-forming bacteria in six clades associated to genera Ensifer, Neorhizobium, Phyllobacterium and Rhizobium. Among NAB, the strain Variovorax sp. CT7.15 was selected due to its capacity to solubilise phosphate and, more interestingly, its high level of aminocyclopropane-1-carboxylate deaminase (ACC deaminase) activity. C. villosa plants were inoculated with representative rhizobia of each phylogenetic group and co-inoculated with the same rhizobia and strain CT7.15. Compared with single rhizobia inoculation, co-inoculation significantly improved plant growth and nodulation, ameliorated plant physiological state and increased nitrogen content in the plants, independently of the rhizobia used. These results support the benefits of pairing rhizobia and selected NAB to promote legume growth in arid or degraded soils.
Highlights
Soils in Tunisia’s arid regions are characterized by low nutrient content, which is often a limiting factor in plant production
Fast-growing rhizobia were identified among isolates from root nodules of C. villosa, which were affiliated to Rhizobium genus [7,8]
The aim of this work was to examine the cultivable biodiversity of nodule-inducing rhizobia and nodule associated bacteria (NAB) in nodules of C. villosa plants growing in arid regions of south Tunisia and to select NAB that could facilitate plant nodulation and growth, in order to establish rhizobia–NAB couples with potential use in the revegetation of these arid soils
Summary
Soils in Tunisia’s arid regions are characterized by low nutrient content, which is often a limiting factor in plant production. These areas suffer from rapid regression of vegetation cover, loss of biodiversity and a significant decline in biological activity [1]. Calicotome spp. nodule-forming bacteria are frequently slow-growing rhizobia affiliated to Bradyrhizobium [5,6]. Contrary to these results, fast-growing rhizobia were identified among isolates from root nodules of C. villosa, which were affiliated to Rhizobium genus [7,8]
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