Interspersed Refuge System

Together, farmers and seed growers are responsible for maintaining an interspersed refuge system in midge tolerant wheat. This is necessary to preserve midge tolerance because:

  • The tolerance is based on a single gene, which has a history of becoming ineffective over time. An interspersed refuge system could extend the life of midge tolerance from as little as 10 years to 90 years or longer
  • It took researchers more than 15 years to move this single gene into spring wheat varieties.
  • No other known source of midge tolerance has been identified so we all need to work together to maintain this valuable trait for today and for generations to come.

What is a Refuge?

The midge tolerant wheat variety is sold as a “varietal blend” which contains 90% midge tolerant variety and 10% midge susceptible variety. The refuge refers to the 10% susceptible variety in the varietal blend (VB).

What is an Interspersed Refuge System?

An interspersed refuge system means that the refuge variety is evenly distributed (inter-seeded) throughout the field. This is different to the Bt corn refuge management system where the refuge is grown as a block beside or within the same field.

The objective of the interspersed refuge system is to prevent the build up of the virulent midge population (virulent midge carry a mutation which allows them to attack midge tolerant varieties). Without it, midge tolerance could break down within 10 years and there is no other known source of midge tolerance.

What are Virulent and Non-Virulent Wheat Midge?

Virulent wheat midge are those which are able to attack plants with the Sm1 gene. They carry a mutation that allows them to attack wheat plants with the Sm1 gene and survive. A very low level of virulent midge exists within the natural midge population.

If virulent midge mate with other virulent midge, a large virulent population quickly builds up and the Sm1 gene could become ineffective within 10 years.

Non-virulent wheat midge (normal midge are considered non-virulent) cannot survive the Sm1 gene contained in midge tolerant wheat. When non-virulent midge feed on the midge tolerant wheat, the seed starts producing higher levels of phenolic acids that cause the larvae to stop feeding and starve to death. If non-virulent midge mate with virulent midge, the progeny of this cross will be non-virulent since non-virulence is the dominant trait.

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