A microscopic image of the conidiophores of Trichoderma harzianum. Mexican researchers claim that a related fungi could act as an environmentally-friendly replacement for the ozone-depleting pesticide, methyl bromide.
Credit: U.S. Department of Agriculture, Agricultural Research Service
ENSENADA: A certain fungus found in soil might be the natural alternative needed to help phase out the use of methyl bromide, one of the most potent ozone-layer depleting substances still used in agriculture.
Traditionally used as a fumigant that sterilizes agricultural soils, food processing facilities and transportation equipment, methyl bromide can also have toxic affects on humans and animals.
Research has shown that nearby exposure to high concentrations can cause central nervous system and respiratory system failures.
The international community has tried to phase out the use of this pesticide, but some countries have resisted these efforts due to the lack of a cost-effective alternative.
However, Mexican researchers have now identified a biological control in the form of a locally found trichoderma fungus, which they claim could be a promising alternative to methyl bromide.
Inhibition of pathogens promising
These fungi grow in almost all agricultural soils in the world. By literally coiling around another host fungi, these particular species degrade cell walls from their target, and some strains even create antibiotic resistance that inhibits other fungi from attacking the plant.
"We achieved up to a 63 percent inhibition of pathogen attacks after experimenting with several trichodermas," explained lead researcher Rufina Hernández, a microbiologist with CICESE, a scientific research institute based in Mexico
"For the past 25 years, scientists have studied several organisms' potential to be used as biocontrol agents, and trichoderma is one of the most widely discussed for its antagonistic capacity against several other fungi," she added.
The methyl bromide legacy
Along with chlorofluorocarbons (CFCs) and other chlorine and bromine-containing compounds, methyl bromide is one of the substances considered by the international scientific community to have strong catalytic agents that deplete the ozone layer in Earth's stratosphere.
Methyl bromide, however, destroys the ozone layer up to 50 times faster than CFCs. Under the Montreal Protocol, which was ratified in 1987, methyl bromide is gradually being phased out internationally because of its environmental impact.
Despite this international accord, some countries have been reluctant to completely stop using it over the lack of a similar cost-effective alternative for agricultural application.
Australia, for example, has heavily restricted methyl bromide use since 2005, but it is still ibeing applied for certified quarantine, pre-shipment and approved feedstock applications, and is still used in packaged rice and soil fumigation for strawberries.
Mexico's eradication effort
In 2005 the Mexican government committed to completely phase out the country's annual use of the pesticide - nearly 1,500 metric tonnes by 2014.
Hernández' research has been instrumental en route to achieving this goal: Baja California's ornamental flower industry, one of the main national consumers of methyl bromide, drastically reduced their chemical usage: from 120 tonnes per year to only 22.5 tonnes in less than five years.
"If you know your enemy, you will find a way to attack it. This meant studying how the farmer's fields were affected and applying a correct biocontrol strategy," said Hernández.
Identifying the biological threat
A team of researchers led by Hernández identified two fungi - fusarium and verticillium - as the pathogens responsible for decreased plant productivity in Baja's flower industry in the past decade.
Both pathogens are notorious in agriculture for their devastating effects in crops: fusarium fungi, for example, are responsible for crown rot and head blight.
Both of these are serious wheat diseases that impact Australia, causing more than $50 million in losses to agriculture each year, according to reports from the CSIRO, Australia's national science organisation.
