Agronomy and Horticulture, Department of

 

The New Bts

Document Type

Learning Object

Date of this Version

2003

Citation

Plant and Soil Sciences eLibrary (PASSeL) Lesson

Comments

Copyright © 2003 Don Lee. Used by permission.

Development of this lesson was supported in part by Cooperative State Research, Education, & Extension Service, U.S. Dept. of Agriculture under Agreement Number 98-EATP-1-0403 administered by Cornell University and the American Distance Education Consortium (ADEC). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S. Department of Agriculture.

Abstract

Bt corn is a general term used to describe corn hybrids farmers buy that have an additional gene added to one on their chromosomes which originated from the soil bacteria Bacillus thuringiensis (Bt). This lesson tells the story of how different hybrids can contain different Bt genes which encode proteins that have toxicity to different corn pest insects.

Introduction

The agronomist pulls their pickup off the road and enters their fourth field of the day. As the sun has climbed in the eastern sky, so has the temperature. The agronomist, however needs to press on since corn borer damage is showing up in their county. They systematically work their way down and across the first rows of corn. In short order, they spot shot holes in the corn and start counting procedures as they transect the field.

[Figure 1. Agronomist scouting a corn field. (Image credit: D. Lee)]

[Figure 2. Corn plant with shot holes. (Image credit: D. Lee)]

Twenty minutes later they are back at the truck and making calculations. The European corn borer damage observed clearly indicates numbers beyond the economic threshold, so they head over to their customer’s place to deliver a treatment recommendation. The farmer won’t like the news, but time is money and treating now will protect a crop that looks great except for the corn borers.

“You saw what in that field?” was the farmer customer’s initial response. “That can’t be right.”

It always takes some time to get to know a new customer, so the agronomist is guarded in their next comments. They start with mentioning the fields scouted yesterday that had corn borer. Other scouts they talked with yesterday were seeing them. It seems to be a good year for corn borer. “But you shouldn’t be finding them in that field . . . it’s a Bt hybrid! Are you sure you were scouting the right field? Is there a way to check the plants and make sure they are really Bt plants? Could the corn borer be resistant to Bt? Maybe you just checked the refuge acres and not the whole field? Are you sure you know what corn borer damage looks like?”

The agronomist takes a breath before proceeding. They know the answer to the last two questions, but pull out the map so the customer can verify they are talking about the same field. Confirming that, the agronomist asks if the hybrid number planted was indeed the number in his notes. “Yes,” emphasizes the customer, “the number I gave you is a new hybrid I’m trying and the salesman said it was a Bt hybrid. Did they give me the wrong stuff?” In a minute the agronomist pulls up hybrid corn information on the laptop. As they read across the trait information for their customer’s number, they find the answer.

The agronomist offers this reply. “There is a test the seed company can do right in the field to verify that those plants have the ‘Bt’ trait you paid for, but observing European corn borer feeding on this hybrid is not unexpected.” The agronomist proceeds to explain to the customer how a plant can be a Bt hybrid but not be designed to kill European corn borer (ECB).

Objectives

  1. Review the concept of “transgenic events” and compare the commercial events developed to control European Corn Borer (ECB).
  2. Predict management implications based on knowing transgene design and other molecular genetic facts.
  3. Describe transgene structure of a new events for control of ECB and why the transgene provides the plant resistance for additional insect pests.
  4. Compare the transgene structure of two new events for Western corn rootworm control in corn.
  5. Explain why genetic transformation technology and plant breeding limitations make it difficult for a company to produce new hybrids with every transgenic trait.

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