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Hybridise GE, non-GE cotton to fight pest resistance
12 May '17
3 min read
Courtesy: University of Arizona
A surprising strategy may counter pest resistance emerging in the genetically engineered crops - hybridising genetically engineered cotton with conventional cotton was found to reduce resistance in the pink bollworm in a study by scientists in the University of Arizona. The study has been published in the Proceedings of the National Academy of Sciences.
The study is the result of a long-standing collaboration between researchers at the University of Arizona and in China. Over 11 years, they tested more than 66,000 pink bollworm caterpillars from China's Yangtze River Valley, a vast region of southeastern China that is home to millions of smallholder farmers.
According to the study's authors, this is the first reversal of substantial pest resistance to a Bt crop. "We have seen blips of resistance going up and down in a small area. But this isn't a blip. Resistance had increased significantly across an entire region, then it decreased below detection level after this novel strategy was implemented," said senior author Bruce Tabashnik, a regents' professor in the UA's College of Agriculture and Life Sciences.
Cotton has been genetically engineered to produce pest-killing proteins from the widespread soil bacterium Bacillus thuringiensis, or Bt. These Bt proteins 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 one billion acres since 1996. But, without adequate countermeasures, pests can quickly evolve resistance.
Insect pests that are rapidly adapting to genetically engineered crops are threatening agriculture worldwide. The primary strategy for delaying resistance is providing refuges of the pests' host plants that do not make Bt proteins. 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 such non-Bt cotton refuges is credited with preventing evolution of resistance to Bt cotton by pink bollworm in Arizona for more than a decade. By contrast, despite a similar requirement for planting refuges in India, farmers there did not comply and pink bollworm rapidly evolved resistance.
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 per cent Bt cotton plants side-by-side with 25 per cent non-Bt cotton plants.
"Because cotton can self-pollinate, the first-generation hybrids must be created by tedious and costly hand pollination of each flower. 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," said Tabashnik, who also is a member of the UA's BIO5 Institute.
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 hybridisation. (SV)
The study is the result of a long-standing collaboration between researchers at the University of Arizona and in China. Over 11 years, they tested more than 66,000 pink bollworm caterpillars from China's Yangtze River Valley, a vast region of southeastern China that is home to millions of smallholder farmers.
According to the study's authors, this is the first reversal of substantial pest resistance to a Bt crop. "We have seen blips of resistance going up and down in a small area. But this isn't a blip. Resistance had increased significantly across an entire region, then it decreased below detection level after this novel strategy was implemented," said senior author Bruce Tabashnik, a regents' professor in the UA's College of Agriculture and Life Sciences.
Cotton has been genetically engineered to produce pest-killing proteins from the widespread soil bacterium Bacillus thuringiensis, or Bt. These Bt proteins 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 one billion acres since 1996. But, without adequate countermeasures, pests can quickly evolve resistance.
Insect pests that are rapidly adapting to genetically engineered crops are threatening agriculture worldwide. The primary strategy for delaying resistance is providing refuges of the pests' host plants that do not make Bt proteins. 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 such non-Bt cotton refuges is credited with preventing evolution of resistance to Bt cotton by pink bollworm in Arizona for more than a decade. By contrast, despite a similar requirement for planting refuges in India, farmers there did not comply and pink bollworm rapidly evolved resistance.
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 per cent Bt cotton plants side-by-side with 25 per cent non-Bt cotton plants.
"Because cotton can self-pollinate, the first-generation hybrids must be created by tedious and costly hand pollination of each flower. 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," said Tabashnik, who also is a member of the UA's BIO5 Institute.
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 hybridisation. (SV)
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