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Segregation of Genes: The Plant Breeder's Method of Predicting the Future

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Creating Wheat Families: Parents → F1 → F2

The goal for the plant breeding team was to create a variety of wheat that was true breeding for ALS herbicide resistance.  This goal was based on the knowledge that wheat farmers would benefit from growing a line of wheat resistant to ALS herbicides (herbicides that inhibit the enzyme acetolactate synthase).  ALS herbicides kill many of the weeds that compete with wheat, so farmers would be able to apply these herbicides over the growing wheat crop to remove competing weeds.  It was also important that the new wheat lines have the good growing and bread making traits current commercial wheat varieties possessed. 

The team crossed the best current wheat varieties with a line that was true breeding for ALS resistance in the greenhouse.

  1. The seeds produced from the Good Variety X ALS line cross were called the F1s.  The F1s were grown in the greenhouse the next year and allowed to self-pollinate to produce F2 seeds.  The F2 seeds were harvested from individual F1 plants. The F2 seeds were put in a packet, and this packet was given a specific family number.
  2. In the fall, the F2 seeds were planted into a family row.  The seeds germinated and developed into plants that grew in the fall and went dormant to overwinter.  The spring revived them from dormancy, and the F2 plants started growing rapidly. 
  3. Before the wheat’s reproductive structures (their heads) emerged, they were carefully sprayed with a rate of the ALS herbicide several times the rate farmers would spray to kill weeds in their fields.
  4. Dr. Baenziger and his team carefully examined each family row that had been sprayed. They examined the plants for evidence of ALS herbicide damage in the plant phenotype.  Data was collected on plants from each row.
  5. At this stage, Dr. Baenziger’s team needed to make selections of individual F2 plants and   predict if the plants selected would be true breeding for ALS resistance.  They made their predictions based on the genetics ideas presented in the following section.

Figure 4. A plant breeder’s nursery. Rows and plots are carefully planted so new lines can be identified. Seeds from a single plot could eventually be planted by wheat farmers on thousands of acres. ALS herbicide was applied to the eight rows in the center of the picture and lines with resistance can be identified.



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