Biological control of Bacillus licheniformis PR2 against Fusarium oxysporum and growth promotion of Pinus strobus L. as an urban greening strategy

• Fusarium oxysporum causes severe growth retardation and mortality in Pinus strobus. • Bacillus licheniformis PR2 suppresses F. oxysporum via cell wall-degrading enzymes. • B. licheniformis PR2 enhances survival rate of P. strobus seedlings. • B. licheniformis PR2 produces IAA to promote root growth and nutrient uptake. • B. licheniformis PR2 improves root collar diameter and biomass in P. strobus seedlings. Eastern white pine ( Pinus strobus L.) is an ever-green conifer with a beautiful rounded pyramidal canopy, growing up to 80 feet tall and 40 feet wide, with a lifespan of approximately 200 years, making it an excellent tree for urban greenery, shade, windbreak, life fence/hedge, as well as for crafts and outdoor chrismas decorations worldwide. However, it is highly susceptible to notorious fungal pathogens such as Fusarium oxysporum at various of growth, from nursery seedlings to mature trees in the field causing lasting effects such as growth retardation or death. Therefore, this study aimed to evaluate the potential of Bacillus licheniformis PR2 as an alternative to chemical fungicides and fertilizers in the management of Fusarium infections and promoting the growth of P. strobus seedlings in the nursery. B. licheniformis PR2 produced fungal cell wall degrading enzymes such as chitinase, β-1,3-glucanase and protease, which degraded chitin, β-glucan and glycoproteins polymers that constitute the cell wall of F. oxysporum . Consequently, the bacterial treatment inhibited spore germination and mycelial growth of F. oxysporum by 85.9.1% and 61.5%, respectively, at 100% concentration of the crude enzyme fraction. The nursery experiment, treatment of P. strobus seedlings with B. licheniformis PR2 culture increased the survival rate of seedlings by 2.3-fold and 2.1-fold compared to chemical treatment and the control groups, respectively. In addition, B. licheniformis PR2 produced up to 108.9 mg/mL of indole-3-acetic acid (IAA), a plant hormone that promotes root growth and lateral root formation, thereby promoting the uptake of water and nutrients by seedlings. Consequently, treatment of P. strobus seedlings with the bacterial culture of B. licheniformis PR2 improved the root collar diameter, dry weight of shoots and roots compared to the chemical treatment and control group, respectively. Therefore, this study demonstrates that B. licheniformis PR2 could be applied as an ecofriendly alternative to chemical fungicides and fertilizers in the sustainable development of urban green spaces, since it can effectively suppress fungal pathogens and promote seedling growth without leaving an environmental footprint or creating a healthy risk to urban residents.