SOUPED-UP FUNGI AIMED AT WEEDS

Researchers Find Early Success With Genetic Engineering

By engineering new genes into plant-killing fungi, scientists in
Israel report they're creating extra-potent biological
weed-whackers.

The fungi, which can be applied via spraying, are still in the
research phase. Before being widely used, said plant scientist
Jonathan Gressel, the gene-modified fungi must be guaranteed safe.

But if super-efficient weed-killing fungi do work and prove harmless,
they could greatly improve farmers' ability to control weeds. Success
should reduce food costs, energy use and herbicide
application.

"Weeds are the main pest restraint on row-crop agriculture," Gressel
and his colleagues, Ziva Amsellem and Barry Cohen, wrote in Nature
Biotechnology. In fact, "the major variable is control of weeds,
whether mechanically or chemically." The researchers work at the
Weizmann Institute of Science, in Israel.

Digging weeds up can lead to erosion and damage to crop plants' roots.
But herbicides create another set of environmental problems, such as
runoff into water supplies and killing nearby plants accidentally, as
well as weeds developing resistance to herbicides.

The souped-up fungi might alleviate such problems with crops as varied
as rice in paddies and the vast fields of vegetables that are grown in
rows. Annually, farmers worldwide spend millions of dollars struggling
to control weeds. In fact, said Gressel, "more than 60 percent of
pesticides used in the developed world are herbicides for weed control."

The problems posed by weeds are so costly and hard to solve that
experts have tried to recruit insects, fungi and other naturally
occurring plant-killing agents that might do the job easier, better or
cheaper. Specific organisms such as fungi have been identified that
naturally attack many of the most troublesome weeds.

According to Gressel, attempts to use natural fungi have provided "a
modicum of control" when the fungi are densely applied. But so far
fungi "have not been sufficiently cost-effective" despite years of
research and "have not met expectations." One reason for
less-than-stellar success is that the fungi and the weeds tend to
develop an evolutionary balance that allows both to survive, "even
when the myco-herbicide [fungus] is used at very high levels."

Application of fungi has also been difficult. For best results
humidity has to remain at almost 100 percent for six to 18 hours after
fungi have been applied. Gressel and his two co-workers tried
engineering the fungal cells to improve performance. One step was to
insert extra "virulence" genes into one strain of the fungus,
Colletotrichum coccodes. The idea was to make the fungus kill weeds
quicker and to make it effective on mature weeds as well as seedlings
or juvenile plants.

Also, the researchers want to keep the fungi from spreading beyond
their target, so they're removing the genes responsible for
sporulation, which is the production of tiny, seed-like spores. This
tactic should stop spore production, or at least disarm the spores.

The Israeli team also showed that adding special new genes made the
fungus much more effective at killing the correct species. And, they
said, the killing effect was extended over a longer period of time,
allowing them to catch weeds that sprouted later.

Eventually, highly specialized fungi might be targeted at plants such
as opium poppies, cocaine and marijuana. This could even open a new
"front" in the drug war.