Apple growers in East Asia may soon have a new tool in their fight against Valsa canker, a devastating stem disease caused by the fungus Cytospora mali. Researchers have identified a soil-derived bacterium, Bacillus amyloliquefaciens strain H12, that demonstrates significant potential as a biocontrol agent, offering an eco-friendly alternative to traditional chemical treatments.
A Dual-Action Approach to Disease Control
The study, published in , details how B. Amyloliquefaciens H12 not only directly inhibits the growth of Cytospora mali but also strengthens the apple tree’s own defense mechanisms. Researchers observed that the bacterium induces abnormal branching in the fungal hyphae – the thread-like structures that allow the fungus to spread – leading to cytoplasmic leakage and cell wall rupture and mycelia death. This direct attack on the pathogen is complemented by the bacterium’s ability to upregulate immune-related gene expression within the apple tree itself.
Specifically, H12 was shown to enhance the accumulation of reactive oxygen species (ROS) and increase callose deposition in the plant. ROS are molecules that plants use to signal and respond to stress, including pathogen attacks, while callose is a polysaccharide deposited in plant cell walls to reinforce them and block pathogen entry. These physiological changes indicate a priming of the plant’s immune system, making it more resistant to infection.
Microbiome Modulation for Enhanced Resistance
Beyond its direct antifungal activity and immune-boosting effects, B. Amyloliquefaciens H12 appears to work by reshaping the bacterial community on the surface of apple leaves – the phyllosphere microbiome. Microbiome sequencing revealed that the introduction of H12 enriches beneficial microorganisms, creating a more favorable environment for plant health and further enhancing host resistance. This holistic approach, targeting both the pathogen and the plant’s natural defenses, is a key strength of the research.
Promising Results in Field Trials
The efficacy of B. Amyloliquefaciens H12 has been demonstrated both in laboratory settings and in field trials. In field tests, the strain achieved a 55.56% disease control efficacy
, suggesting a substantial reduction in the severity of Valsa canker. This level of control is particularly encouraging given the challenges associated with managing fungal diseases in agricultural systems, where environmental factors and pathogen evolution can quickly diminish the effectiveness of control measures.
Bacillus amyloliquefaciens: A Versatile Biocontrol Agent
Bacillus amyloliquefaciens is gaining recognition as a versatile biocontrol agent with applications extending beyond apple orchards. A review published in June highlights the bacterium’s potential in metabolic engineering and protein expression, as well as its role in producing chemicals, enzymes, and other industrial bioproducts. The review emphasizes the bacterium’s capabilities as a biofertilizer and its antifungal, antibacterial, and antiviral properties.
The Bacillus amyloliquefaciens group – encompassing B. Amyloliquefaciens, B. Velezensis, B. Nakamurai, and B. Siamensis – has emerged as a promising source of biocontrol agents for managing pathogenic fungi, including postharvest diseases. These species employ various antifungal mechanisms, including the production of antifungal lipopeptides and volatile organic compounds, competition for nutrients, and the induction of disease resistance in host plants.
Future Directions and Engineering Potential
Despite its promise, researchers acknowledge that B. Amyloliquefaciens remains insufficiently studied
. The June review points to a need for further research and the development of advanced engineering methods and gene editing technologies specifically tailored for this bacterium. Unlocking the full potential of B. Amyloliquefaciens will require a deeper understanding of its genetic tools and metabolic capabilities, paving the way for optimized strains and more effective biocontrol strategies.
The plant growth-promoting (PGP) mechanisms of B. Amyloliquefaciens have attracted significant attention, solidifying its position as a highly effective biofertilizer and biocontrol agent in agriculture. The identification and characterization of strain H12 represents a significant step forward in harnessing the power of this bacterium to combat Valsa canker and promote sustainable apple production.