The Simultaneous Role of Plant Growth Promoting Bacteria (PGPB) in Biological Control and Improving the Production of Forest Resources

Abstract

Plant pests and fungal diseases cause tremendous damage to forest resources worldwide, leading to increasing with increasing leading economic losses due to the impact of climate change such as increased prevalence and proliferation of invasive species. Especially in the field of forestry and horticulture, these fungal diseases and pests are the main cause of growth delays and deaths of forest seedlings, as well as lowering fruit quality and yield in fruit trees. Most nurseries and orchards around the world rely on chemical fungicides and pesticides as a means of responding quickly to fungal diseases and pests. However, these chemicals are subject to strict laws and regulations due to environmental pollution, their negative impacts on human health (direct chemical toxicity and chemical residues in food products) and the emergence of resistant pests and pathogens which increase the burden of pest and disease control, as well as the increased costs of food quality assurance, leading to a rise in overall costs of production. In addition, macronutrients such as nitrogen (N) and phosphorus (P) are essential for the growth of seedlings and the production of high-quality fruits and are often replenished using chemical fertilisers. However, chemical fertilisers cause soil acidification, leaching, water pollution (and eutrophication), emission of greenhouse gases, formation of toxic compounds and the disruption of soil microbial balance, leading to the proliferation of phytopathogenic fungi that exacerbate plant health challenges. In the recent past, plant growth promoting bacteria (PGPB) such as Bacillus species have been demonstrated as an important alternative to the use of chemical fungicides, pesticides and fertilisers. The popularity of Bacillus spp. in forestry is mainly due to their potential to effectively control insect pests and plant diseases while simultaneously promoting the growth of forest trees and improving fruit production, using various mechanisms. Bacillus spp. have become a focus for research as a next-generation solution in the fields of biological control, biostimulation and biofertiliser science, with the potential to reduce the dependence on chemical fungicides, pesticides and fertilisers. This review provides an overview of the potential role of the hydrolytic enzymes such as chitinase, β-1,3-glucanase and protease produced by Bacillus species as versatile weapons in the biological control of fungal phytopathogens/insect pests through the degradation of fungal cell walls/insect pest cuticles, respectively. In addition, this study reviewed the biostimulation properties of Bacillus spp. such as the secretion of phytohormones like indole-3-acetic acid (IAA) which promote root growth and gibberellic acid (GA) which promotes fruit development. The study also examines the biofertilisation potential of Bacillus spp. through N-fixation/ammonia-N production and phosphate (PO₄³⁻) solubilisation, which increase the availability and plant uptake of essential nutrients such as nitrogen and phosphorus in the soil. This review highlights the simultaneous biological control of major plant pathogenic fungi and insect pests and the plant growth-promoting properties of Bacillus spp. that could be harnessed as suitable alternatives to chemical use in the management of fruit trees and other forest resources.