Abstract
Desert plants are able to survive under harsh environmental stresses inherent to arid and semiarid regions due to their association with bacterial endophytes. However, the identity, functions, and the factors that influence the association of bacterial endophytes with desert plants are poorly known. These bacterial endophytes can be used as an untapped resource to favor plant growth and development in agro-ecosystems of arid regions. The present study is therefore focused on the isolation and identification of bacterial endophytes from two native medicinal plants (Fagonia mollis Delile and Achillea fragrantissima (Forssk) Sch. Bip.) growing spontaneously in the arid region of the South Sinai (Egypt), and characterization of their plant growth promoting (PGP) traits. Thirteen putative bacterial endophytes were isolated from the leaves of both plant species and characterized for their plant growth promoting abilities using molecular and biochemical approaches, as well as greenhouse trials. Selected endophytic bacterial strains were applied to maize plants (Zea mays L. var. Single cross Pioneer 30K08) to further evaluate their PGP abilities under greenhouse conditions. Isolated bacterial strains have variable plant growth promoting activities. Among these activities, isolated bacterial endophytes have the efficacy of phosphate solubilizing with clear zones ranging from 7.6 ± 0.3 to 9.6 ± 0.3 mm. Additionally, the obtained bacterial endophytes increased the productivity of indole acetic acid (IAA) in broth media from 10 to 60 µg·mL−1 with increasing tryptophan concentration from 1 to 5 mg·mL−1. Bacillus and Brevibacillus strains were frequently isolated from the leaves of both plant species, and had significant positive effects on plant growth and shoot phosphorus (P) and nitrogen (N) contents. Results suggest that these endophytes are good candidates as plant growth promoting inoculants to help reduce chemical input in conventional agricultural practices and increase nutrient uptake and stress resilience in plant species.
Highlights
The enhancement of crop productivity is required for feeding the increasing population in developing countries and often relies on the use of chemical fertilizers
Thirteen endophytic bacterial strains were isolated from the leaves of the two medicinal plants (Table 2)
Nine strains were isolated from F. mollis plants and identified as Bacillus spp., and Paenibacillus sp., while four bacterial strains were isolated from A. fragrantissima plants and identified as Paenibacillus sp. and Brevibacillus sp
Summary
The enhancement of crop productivity is required for feeding the increasing population in developing countries and often relies on the use of chemical fertilizers. Long-term use of these fertilizers was shown to decrease bacterial diversity in soil [1,2] and can have harmful effects on the environment, such as leaching of phosphorus and nitrogen into groundwater, and increasing soil and groundwater pollution [3]. One way to increase the sustainability of agricultural practices is the use of efficient, nutrient mobilizing microorganisms to reduce the need and dependency on chemical fertilizers [4,5]. Bacterial endophytes colonize plant tissues without any apparent pathogenic symptoms and establish beneficial associations with their plant host through phytohormone synthesis, enzyme production, and nutrient mobilization and translocation, such as phosphate (PO4 −3 ). Many endophytes display various applications such as antimicrobial mechanisms, which reduce crop losses caused by pathogens [12,13,14,15,16], and its metabolites integrated into different biotechnological applications [17,18,19,20]
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