Controlling Pathogens With Organic Biocontrol Agent Bacillus amyloliquefaciens

Bacillus amyloliquefaciens (BAA) is a type of bacterium that is found in soils throughout the world and also on dried foods and fresh produce.

Many strains of these bacteria enhance plant growth and inhibit plant pathogens, greatly improving the health of plants. They colonize the roots of plants and reduce plant disease by both direct and indirect action.

A legume root with nodules attached housing Plant growth-promoting rhizobacteria.

BAA strains produce a number of chemicals, including a number of antibiotics that inhibit the germination of fungal spores and the growth of the fungi. In addition, the bacteria stimulate the plant to activate their natural resistance mechanisms. This provides additional control of pathogens.

Many strains of BAA are so helpful to plants that they are known as plant growth-promoting rhizobacteria (PGPR) – a designation for powerful bacteria that improve plant health.

We at Gardener’s Path will review how Bacillus amyloliquefaciens can improve plant health and provide tips on how to use these biocontrol agents.

BAA Strains Vary in Their Properties

Just like the closely related bacteria Bacillus subtilis, B. amyloliquefaciens is composed of many different strains, which vary in their production of antibiotics and ability to colonize plants.

Top down view of Bacillus amyloliquefaciens growing in a petri dish on a black backgrround.

Research has been conducted on a dizzying array of strains, but most commercial formulations are comprised of a few key strains, especially D747 (often sold as Double Nickel or Stargus).

The powerhouse strain FZB42 that is sold commercially has been found to be a different species of Bacillus and is now known as B. venezensis.

How Can BAA Help Your Garden?

The biopesticide BAA can both help prevent damage from pathogens and act as a biofertilizer. These bacteria live in a prime location – they are components of the rhizosphere – the lush area around plant roots where the plants secrete sugars and vitamins that benefit the growth of the microbes in this area.

In addition, a number of companies sell BAA to control a variety of plant-parasitic nematodes.

The Bacteria Colonize Plant Roots

BAA starts its growth on the primary roots. First, it grows underneath the outermost cells. Then it spreads along the root surfaces.

By being in this key location, the bacteria block the growth of pathogens on the roots.

The plants also benefit from the presence of BAA because these bacteria produce compounds that stimulate plant growth and are taken up by the roots.

Plant growth-promoting rhizobacteria growing in nodules on a pea root.

This makes these bacteria plant growth-promoting rhizobacteria (PGPR) – like their close relative Bacillus subtilis.

The end result is that plants grow better due to the fertilization that the bacteria provide. They provide both nitrogen and phosphorus.

In addition, BAA activates the plants’ own resistance system, which is active throughout the whole plant. This helps the plant fend off foliar pathogens.

BAA Outcompetes Other Microbes

These bacteria use several mechanisms that enable them to prevail over other microbes in the soil. First, they tie up key nutrients that other organisms need for survival.

For example, iron is necessary for growth and is present at low concentrations in the soil. BAA produces compounds called siderophores that bind the iron and prevent other microbes from accessing it.

They also produce antibiotics that affect other microbes. Like Bacillus subtilis, BAA produces compounds like iturins and fengmycin that inhibit the germination of fungal spores and the development of the fungal germ tubes.

In addition, the bacteria produce enzymes that break down other microbes! BAA can produce antibiotics that dissolve other bacteria. And some strains produce chitinases – enzymes that break down the fungal cell walls that are composed of chitin.

Bacillus amyloliquefaciens is Highly Resistant to Chemicals

These bacteria have another advantage over other bacteria in the soil – they are unusually resistant to the chemicals that plants produce to defend themselves.

Not only that – they are also normally unaffected by nematicides, herbicides, and most fungicides.

They could be affected by antibiotics used to control plant pathogenic bacteria, but these compounds are usually only applied to the leaves of apple or pear to control fire blight. It is highly unlikely that foliar antibiotic applications would affect soil inoculants.

BAA is Safe for Humans and Other Organisms

Since BAA is a common soil inhabitant and is found naturally on fresh produce, it is likely that people are exposed to it on a regular basis. The species is not known to produce any toxins that affect mammals and has never been associated with food-borne disease outbreaks.

Extensive testing for the registration of strain D747 as a pesticide with the Environmental Protection Agency (EPA) found no effect on non-target organisms, including rats, fish, honeybees, and plants.

A farmer spays the earth with a solution containing Bacillus amyloliquefaciens.

The only requirements for personal protective gear are for pesticide handlers that would frequently be exposed to the strain for prolonged periods. They are required to wear long-sleeved shirts, a dust/mist filtering respirator, and waterproof gloves.

Plant Pathogens Targeted by Bacillus amyloliquefaciens

This organism affects a range of fungal and bacterial pathogens. The original EPA application lists both soilborne and foliar pathogens.

Soilborne fungal pathogens include Fusarium, Pythium, Rhizoctonia, Phytophthora, and Verticillium, while foliar ones include several rusts, powdery mildew, downy mildew, Botrytis cinerea, and Alternaria.

Foliar bacterial pathogens include Pseudomonas syringae pv. tomato and Xanthomonas. In Canada, the strain is registered to use as a preventative measure to control fire blight.

How to Apply BAA to Prevent Plant Disease

While B. amyloliquefaciens will not cure plant diseases, it can prevent a number of them from occurring on vegetables, turf, fruit trees, ornamentals, and greenhouse plants.

Two different sized plastic bottle of BONIDE® Revitalize® Biofungicide on a white, isolated background.

BONIDE® Revitalize® Biofungicide with  B. amyloliquefaciens

BAA comes in two types of formulations. One is a water soluble powder that can be sprayed, applied with ground equipment, or added into irrigation.

Monterey Complete Disease Control in different sized container on a white, isolated background.

Monterey Complete Disease Control

The other type is a talc-based powder that is applied in a dry planter box.

Arbico Organics provides a number of products that contain BAA.

These bacteria don’t survive storage as long as other soil inoculants, and you should be careful about storing them as recommended on the label.

You will also need to reapply the bacteria each season. They don’t cause long-term changes in the soil.

You can combine BAA with other soil inoculants. Trichoderma and arbuscular mycorrhizal fungi (AMF) can all coexist with Bacillus amyloliquefaciens.

Naturally Occurring Bacillus amyloliquefaciens Offers Many Benefits

Bacillus amyloliquefaciens colonizes plant roots, putting it in a prime position to outcompete pathogens for growth on the plant.

These bacteria fertilize the plant by providing nutrients that are in short supply and producing chemicals that induce the plant grow. They also induce the plant to activate its own resistance mechanism, therefore controlling even more pathogens.

This species of Bacillus also outcompetes other microbes in the soil and can inhibit both bacteria and fungi.

Have you used BAA to prevent disease in your garden? If so, let us know how it worked in the comments.

And read on for information on other biofungicides and biopesticides to include:

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via Lawn and Garden Inc and Bonide/Control Solutions. Uncredited photos: Shutterstock.

About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the knowledge that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

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