Shifts in the Rhizosphere Bacterial Community and Improved Essential Oil Yield and Quality in Chamomilla recutita L. Plant Through Cyanobacterial Inoculation

Rhizosphere bacterial communities play a crucial role in improving nutrient availability, disease and stress resistance, and overall development in plants. Biofertilizers can enhance plant growth, but little is known about their mode of interaction. Here, we studied the impact of seedling coating with two nitrogen-fixing cyanobacterial strains, Nostoc sp. NoHu, or Anabaenopsis circularis AnHu, on chamomile (Chamomilla recutita L.) growth, essential oil yield and quality, apigenin-7-O-glucoside, and the composition of rhizosphere bacterial communities, under field conditions in Egypt. The rhizosphere bacterial community, analyzed by 16 S rRNA amplicon libraries, composed of 31 phyla and 164 different genera. Compared to untreated plants, the application of both strains showed contrasting effects. Nostoc sp. application significantly enhanced almost all tested plant growth parameters, including fresh and dry weights of shoots, roots, and flowers, as well as the yield and content of vital essential oil constituents and the apigenin-7-O-glucoside. Furthermore, Nostoc sp. application increased both the abundance and diversity of the rhizosphere bacterial community compared to untreated plants, suggesting an indirect effect mediated through altering the rhizosphere bacterial community structure. In contrast, A. circularis application negatively affected essential oil yield and quality, exhibited the lowest bacterial abundance and diversity. These findings highlight potential of Nostoc sp. NoHu to boost chamomile productivity and essential oil quality. The contradictory responses between the two cyanobacterial strains emphasize strain-specific effects with Nostoc sp. NoHu as a promising biofertilizer candidate for chamomile.