Topic Proposal
5/7/09
Science Research
Mr. Guastella
Using Bacillus subtilis For Biocontrol
Losses from plant diseases also can have a significant economic impact, causing a
reduction in income for crop producers and distributors and higher prices for consumers.
In 1993 the United States lost more than one million acres (405,000 hectares) of crops to
disease. More than 800,000 acres of wheat succumbed to disease, exacting a monetary
loss in the millions of dollars. Another example of plant diseases were Irish famine which
caused many deaths. And these plant diseases still cause economic problems in the
societies. For a number of years, it has been known that various microorganisms exhibit
biological activity so as to be useful to control plant diseases.
Every year 250-300 million dollars of chemical pesticides are used to control corn
rootworm infestations. Many of these chemical pesticides are toxic to humans, wildlife
and other nontarget species. Also some have been found in the ground water. New
chemical insecticides cost $100 million to develop. Biological control offers an attractive
alternative to synthetic chemical fungicides. Biopesticides (living organisms and the
naturally produced compounds produced by these organisms) can be safer, more
biodegradable, and less expensive to develop.
As used herein, "biological control" is defined as control of a pathogen or insect
by the use of a second organism. Known mechanisms of biological control include
enteric bacteria that control root rot by out-competing fungi for space on the surface of
the root. Bacterial toxins, such as antibiotics, have been used to control pathogens. The
toxin can be isolated and applied directly to the plant or the bacterial species may be
administered so it produces the toxin in situ.
There are approximately 40 biocontrol products commercially available for the
control of plant diseases worldwide. Biocontrol products are available to control many
diverse pathogens, as recently reviewed by Fravel, et al., "Availability and Application
of Biocontrol Products," Biological and Culture Tests for Control of Plant Diseases, 11:17 (1996). At least 27 genera of fungi, 3 genera of bacteria, and 4 genera of nematodes are
targeted for control by these products. More than half of these products control soilborne
fungi. The biocontrol agents themselves are also diverse and include at least 9 genera of
fungi, 4 genera of bacteria, and one actinomycete. Biocontrol products are used on a great
variety of crops including greenhouse crops, row crops, field crops, perennial field crops,
and trees and wood, as well as in special cropping systems such as mushroom cultivation.
The products are applied in many ways. They may be sprayed onto plants or harvested
fruits, drenched on harvested fruit or on plants, incorporated into the soil, applied as root
dips, used to treat seeds, or inserted into trees or wood products. Biocontrol products
currently on the market in the U.S. include Aspire.
The biocontrol agents are useful in a method of imparting to plants protection
against plant pathogens. This method involves applying the biocontrol agent to plants,
plant seeds, or soil surrounding plants under conditions effective to impart disease
protection to plants or plants produced from the plant seeds. The present invention is also
directed to a method of enhancing plant growth. This involves applying the biocontrol
agent to plants, plants seeds, or soil surrounding plants under conditions effective to
enhance growth in the plants or plants produced from the plant seeds. The present
invention also relates to a supernatant obtained from a culture of either one of the
Bacillus subtilis, Pseudomonas putida, or Sporobolomyces roseus biocontrol isolates,
where the supernatant includes an antifungal metabolite produced by the respective
biocontrol isolate. The biocontrol agents of the present invention are highly useful in
agriculture to protect plants from a variety of plant bacterial, fungal, and viral diseases. In
addition, these agents can enhance the growth of treated plants. Significantly, these
effects are achieved without being hazardous to animals or humans.
Bacillus sbutilisBacillus species as a group offer several advantages over other bacteria for
protection against root pathogens because of their ability to form endospores, and
because of the broad-spectrum activity of their antibiotics.
This bacteria shows strong antibiosis against Cochliobolus sativus (spot
blotch/common root rot of cereals), Colletotrichum graminicola (corn anthracnose),
Fusarium graminearum (scab of cereals, ear/stalk rot of corn), Fusarium moniliforme
(ear/stalk rot of corn), Pyrenophora tritici-repentis (tan spot of wheat), Stagonospora
nodorum (Stagonospora nodorum blotch of wheat), Stagonospora avenae f. sp. triticea
(Stagonospora avenae blotch of wheat), and Stenocarpella maydis (stalk/ear rot of corn).
The Bacillus subtilis of the present invention shows excellent control of seed borne
transmission of Cochliobolus sativus, Pyrenophora tritici-riepentis, and Fusarium
graminearum in wheat and of Fusarium moniliforme in corn. It also prevents aerial
inoculation of flowering wheat spikes with Fusarium graminearum, diminishes grain
infection frequency by Fusarium, reduces grain weight reduction by Fursarium, and
dramatically reduces grain contamination by Fursarium mycotoxin deoxynivalenol. In
addition, this bacterium may be used to reduce contamination of grains and other plant
products with harmful secondary fungal metabolites. The endophytic capability of this
bacterium suggests additional applications for plant disease control. Seedlings and other
plant propagative units can be inoculated for long-term plant protection.
DiseasesCurrent practices for controlling plant diseases are based largely on disease
resistant crops, cultivation management in fields and application of synthetic pesticides
(Elizabeth and Emmert, 1999). Biological control using antagonistic microbes to reduce
the use of chemical pesticides in a system of integrated plant disease management, offers
a powerful alternative to control plant diseases.
Fusarum head blight (FHB), primarily caused by F. graminearum, is a
devastating disease that results in extensive yield and quality losses to wheat and barley
throughout the world (Urrea et al., 2002; Capettini et al., 2003). After infection,
Fusarium mycotoxins are accumulated and the products of these crops are harmful to
both people and animal stock (Ingalls, 1996; Onji et al., 1998; Placinta et al., 1999).
Among the pathogens, F. graminearum is the most common Fusarium species producing
deoxynivalenol (DON) (Olsson et al., 2002).
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