Mighty Microbes Part II: Microbial Weapons for Agricultural Production

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Microbial Weapons for Agricultural Production

During the early 20th century, soil microbiology and ecology studies led to the identification of many microorganisms that act as antagonists or hyperparasites of pathogens and insect pests. This was the origin of a popular research topic, biological control, the use of an organism or organisms to reduce disease (caused by plant pathogens) or damage (caused by insect pests). This often resulted in the release of several predators, parasitoids, and pathogens of insects and plants until the mid 1900’s. Many showed promise in field-scale inoculations, but few were developed commercially because of the rapid adoption of less expensive and more consistently performing chemical pesticides.

Early examples of biological control first emerged in the second century and mostly involved insect predators and parasites of undesirable insect pests.  The first microbial biological control agent was observed in 1901 when Shigetane Ishiwatari isolated a bacterium causing “soto” (sudden-collapse) disease of Japanese silkworms. The bacterium was again isolated from Mediterranean flour moths by Ernst Berliner in 1911 and was named Bacillus thuringiensis after the German town, Thuringia, where the moth was found. The French used B. thuringiensis as a biopesticide in the 1920’s and the bacterium became commercially available in 1938 as “Sporine.” It finally appeared in the US in 1958 and was registered by the EPA in 1961.

Until the 1960’s and the suppressive soil work of Drs. Cook, Thomashow, and Weller, the role of individual microorganisms in the soil was unclear. Their analytical ability and solid microbiology, biochemistry, and genetic skills painted a clear picture of the nature and mechanism of how Pseudomonas fluorescens strain 2-79 was able to suppress the Take-all pathogen, Gaeumannomyces graminis var. tritici. This work set a standard for studies on biological control with microbes and was followed by a flush or reports on soil bacteria that had beneficial effects on plants such as improved growth, pathogen suppression, and induced plant resistance.  These bacteria were called Plant Growth-Promoting Rhizobacteria (PGPR) and included the genera Alcaligenes, Agrobacterium, Arthrobacter, Azospirillum, Azotobacter, Bacillus, Burkholderia, Enterobacter, Klebsiella, Streptomyces, Pseudomonas, and Serratia.  Several have been commercialized as biofertilizers (nitrogen fixation or improved nutrient acquisition), bio protectants (disease suppression), or as inducers of plant disease resistance.

There was a resurgence of interest in biological agents as the costs of overusing synthetic chemicals became apparent and pesticide resistant insects started to appear. The expansion of organic agriculture also spurred research and development of biopesticides. Since 1995, more than 100 biopesticides have been registered with the EPA. Commercial success stories from the 1980’s and 1990’s include products containing Agrobacterium radiobacter for the prevention of crown gall on woody crops and Pseudomonas fluorescens for the prevention of fire blight in orchards where the antibiotic streptomycin had been overused and resistant pathogen populations were abundant. In the greenhouse and potting mix industry, products containing a variety of microbes that suppress soil borne pathogens were introduced into the market.

The microbes used in today’s agriculture can be separated into two groups, bio protectants and probiotics. Bio-protectants include microbes or derivatives from microbes that are used for biological control. These function via one or more mechanisms such as rhizosphere competitiveness, site affinity, antibiotic production, hyper parasitism, or induced host plant resistance. Some products are approved for organic use while others were developed for conventional farming.

Probiotics include microbes or derivatives of microbes and function via mechanisms such that either improve nutrient availability to the plant, or stimulate nutrient uptake and utilization. We will discuss these in more detail in the third and last installment of this series of blogs.

Below is a brief list of biologicals to illustrate the options available to growers. It is by no means a complete list of biologicals nor is meant to be a list of organic options for disease and pest management as many other organic options such as potassium bicarbonate and kaolin clay are not included.

Examples of Biopesticides

Type

Product

Manufacturer

Organism

Mechanism

Target

Bactericide

 

NoGall

BASF

Agrobacterium radiobacter A84

Competitive exclusion

Agrobacterium tumefaciens

Bactericide/Fungicide

       
 

Cease

BioWorks

Bacillus subtilis QST 713

Antibiotics

Several bacterial and fungal diseases

 

Serenade

Bayer

Bacillus subtilis QST 713

Multiple

Several bacterial and fungal diseases

Fungicide

 

Bio-Tam©

(OMRI)

Marrone BioInnovations

Trichoderma gamsii and T. asperellum

Hyperparasitism

Soil-borne fungal pathogens

 

Botector®

(Organic)

Bio-Ferm (Austria)

Aureobasidium pullulans

Competitive exclusion

Botrytis, Anthracnose, Phomopsis, Rhizopus, Monilinea

 

Cabrio®, Headline®, Insignia)

BASF

Synthetic derivative based on Strobilurus tenacellus

Pyraclostrobin metabolic inhibitor

Broad spectrum fungicide

 

Contans WG

Bayer and other Manufacturers

Coniothyrium minitans

Hyperparasitism

Sclerotinia diseases, Downy Mildew

 

Disarm®

Arysta LifeScience

Synthetic derivative based on Strobilurus tenacellus

Fluoxastrobin

Broad spectrum fungicide

 

FLINT®, Stratego®, Compass®

Bayer

Synthetic derivative based on Strobilurus tenacellus

Trifoxystrobin, metabolic inhibitor

Broad spectrum fungicide

 

Regalia®

Marrone BioInnovations

Extract of Reynoutria sachalinensis

Induced systemic resistance

Broad spectrum fungicide

 

RootShield (OMRI)

BioWorks Inc.

Trichoderma harzianum T-22

Hyperparasite

Various fungal parasites

 

Quadris®,

Syngenta (Zeneca)

Synthetic derivative based on Strobilurus tenacellus

Azoxystrobin (kresoxim-methyl) metabolic inhibitor

Broad spectrum fungicide

 

Several Products

Several Suppliers

Paecilomyces fumosoroseus

Hyperparasitism

Insects and nematodes

Herbicide

 

Basta®, Finale®, Rely®, Liberty®

Bayer CropSciences

Glufosinate- -ammonium naturally produced by Streptomyces viridochromogenes and S. hygroscopicus

Metabolic inhibitor

Broad spectrum herbicide

Insecticide

 

Avermectin products

Several Suppliers

Streptomyces avermitilis

Insect nerve toxin

Ants, mites, roaches and other insects

 

Botanigard 22 WP or ES

BioWorks, Inc.

Beauveria bassiana GHA

Hyperparasitism

Broad spectrum insecticide

 

Grandevo ®

(OMRI)

Marrone BioInnovations

Chromobacterium subtsugae PRAA4-1

Insect pathogen

Broad spectrum insecticide

 

Madex®

Certis USA

Cydia pomonella granulovirus

Viral pathogen

Codling moth

 

NemAttackTM

Arbico (supplier)

Steinernema carpocapsae

Parasitism

Armyworm, cutworm, weevils, fleas, flies, and others.

 

NemaseekTM Hb

Arbico (supplier)

Heterorhabditis bacteriophora

Parasitism

Ground dwelling insects.

 

Scanmask

BioLogic

Steinernema feltiae

Parasitism

Soil and wood boring insects.

 

St. Gabriel’s Milky Spore

St. Gabriel’s Organics

Bacillus popillae and B. lentimorbus

Parasitism

Insect grubs

 

Monterey Garden Insect Spray (OMRI)

Monterey Lawn and Garden

Spinosad (mixture of Spinosyn A and D)

Insect nerve poison

Broad spectrum insecticide

 

Multiple Products

Multiple manufacturers

Bacillus thuringiensis var.  kurstaki

Parasitism

Butterfly and moth larvae

 

Multiple Products

Multiple Manufacturers

Bacillus thuringiensis var. israelensis

Parasitism

Mosquito, black fly, fungus gnat

 

Mycotrol® ESO/WPO

BioWorks

Beauveria bassiana

Parasitism

Whitefiles, mealybugs, thrips, aphids, others

 

Venerate®

(OMRI)

Marrone BioInnovations

Burkholderia spp. A396

Insect pathogen

Broad spectrum insecticide

 Nematicide

 

Majestene®

(OMRI)

Marrone BioInnovations

Burkholderia spp. A396

Nerve toxin

Broad spectrum soil insects and nematodes

 

Several Products

Several Suppliers

Paecilomyces lilacinus

Hyperparasitism

Nematodes

At present, there are a number of biological options for disease and insect management. Either the organisms themselves or their metabolites are used for commercial product production.  The majority of the products target insect pests and fungal pathogens of plants. Most use microorganisms as the active ingredient. There are a few that use extracts from microorganisms that function as insect nerve or fungal metabolic toxins.  

Many of the products are OMRI approved or regarded by the EPA as reduced risk pesticides.  One group of reduced risk pesticides is the strobilurins.  Based on a naturally occurring metabolic inhibitor secreted by the pinecone fungus, Strobilurus tenacellus, Strobilurins represent a major development in fungus-based fungicides. The original molecules produce by the fungus was sensitive to light and high vapor pressure. Zeneca initiated chemical studies in the 1980’s and registered a stable derivative name azoxystrobin or kresoxim-methy with the EPA in 1986.  BASF synthesized the first commercial version in 1996 as Cygnus and Sovran.  In 2002, BASF introduce a new synthetic derivative, pyraclostrobin and marketed it as (Cabrio®, Headline®, and Insignia®).  Later, combination products Opera® (pyraclostrobin and kresoxim-methyl) and Pristine® (pyraclostrobin and boscalid) were introduced to help prevent resistance.

One product, Regalia®, derived from the Giant Knotweed (Reynoutria sachalinensis), was included as it introduces another mechanism of action.  Also from Marrone BioInnovations, recent product registrations have improved our situation for nematode (Majestene®) and insect (Venerate®) control. We are indeed in exciting times as the number of natural options for disease and pest management increase. The larger our arsenal becomes, the easier it will be to reduce the risk of resistance developing in the target populations by using products with different modes of action.

Thus, there are many biologically-based product to address pathogens and pests of plants. Each year, more discoveries, and new products become available. These products, combine with a good crop management program, will enable successful organic crop production.

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