Collaborative effort by
researchers in China and the University of Arizona find unique method to
reverse resistance of pink bollworm to Bt cotton. Implications exist for
transgenic corn and soybeans as well.Researchers with the University of
Arizona and China discovered a surprising strategy to reverse pink bollworm
resistance to genetically engineered cotton.Cotton growers have been able to
use genetically engineered cotton to fight the pink bollworm. This has happened
as scientists have been able to produce pest-killing proteins from the
widespread soil bacterium Bacillus
thuringiensis, or Bt. Without adequate countermeasures, scientists have
discovered that pests can quickly evolve resistance.
According Bruce Tabashnik, one of the authors of the
study and a regents’ professor with the University of Arizona, these Bt
proteins are considered environmentally friendly because they are not toxic to
people and wildlife. They have been used in sprays by organic growers for more
than 50 years, and in engineered Bt crops planted by millions of farmers
worldwide on more than 1 billion acres since 1996.Scientists from the U.S. and
China discovered that by hybridizing genetically-engineered cotton with conventional
cotton, it reduced the resistance of the pink bollworm. Details of the 11-year
study that tested more than 66,000 pink bollworm caterpillars from China’s
Yangtze River Valley are published.
Tabashnik says this is the first-ever case where
scientists have seen substantial reversal to resistance developed by a pest.The
primary strategy for delaying resistance is providing refuges of the pests’
host plants that do not make Bt proteins, according to Tabashnik. This allows
survival of insects that are susceptible to Bt proteins and reduces the chances
that two resistant insects will mate and produce resistant offspring.Before
2010, the U.S. Environmental Protection Agency required refuges in separate
fields or large blocks within fields. Planting non-Bt cotton refuges is
credited with preventing evolution of resistance to Bt cotton by pink bollworm
in Arizona for more than a decade.
The ingenious strategy used in China entails
interbreeding Bt cotton with non-Bt cotton, then crossing the resulting
first-generation hybrid offspring and planting the second-generation hybrid
seeds. This generates a random mixture within fields of 75 percent Bt cotton
plants side-by-side with 25 percent non-Bt cotton plants, according to the
University of Arizona. Because cotton can self-pollinate, the
first-generation hybrids must be created by tedious and costly hand pollination
of each flower,” said Tabashnik, “However, hybrids of the second generation and
all subsequent generations can be obtained readily via self-pollination. So,
the hybrid mix and its benefits can be maintained in perpetuity.”
Tabashnik calls this strategy revolutionary because it
was not designed to fight resistance and arose without mandates by government
agencies. Rather, it emerged from the farming community of the Yangtze River
Valley. While most previous attention has focused on the drawbacks of
interbreeding between genetically engineered and conventional plants, the
authors point out that the new results demonstrate gains from such
hybridization. For the growers in China, this practice provides short-term
benefits,” Tabashnik added. “It’s not a short-term sacrifice imposed on them
for potential long-term gains. The hybrid plants tend to have higher yield than
the parent plants, and the second-generation hybrids cost less, so it’s a
market-driven choice for immediate advantages, and it promotes sustainability.
Our results show 96 percent pest suppression and 69 percent fewer insecticide
sprays.”A great thing about
this hybrid seed mix strategy is that we don’t have to worry about growers’
compliance or regulatory issues,” Tabashnik said. “We know it works for
millions of farmers in the Yangtze River Valley. Whether it works elsewhere
remains to be determined.”
Source: Daily Freeman, U.S.A Wednesday, 10 May 2017