Thursday, January 21, 2010

Open Pollinated Corn - Part Two

Why Hybrid Corn Seed Can’t Be Saved and Unintended Consequences

Hybrid corn seed cannot be saved and replanted because hybrid varieties do not “breed true” in following generations. The reason for this is that in the hybrid variety each plant had one gene from the male parent and one gene from the female parent for every plant trait. This is what produced the uniformity in maturity, height, etc. which was so beneficial for machine harvesting. But when the seed from a hybrid variety is saved and replanted, the resulting plants have a random assortment of gene pairs for each trait, producing plants of varying maturities, heights, etc. Thus the advantage of the hybrid variety is lost if seed is saved and replanted. The farmer needs to buy new seed every year in order to have the advantages of planting hybrid seed. Clearly the benefits of hybrid varieties were worth this extra cost to farmers as adoption of hybrid varieties was rapid. Farmers quickly developed loyalties to particular seed companies and varieties and paid premium prices for hybrid seed which continued to yield ever more bountiful harvests throughout the 1940s, 1950s and 1960s. There seemed to be no drawbacks to the use of hybrid corn seed.

A chink in the hybrid corn armor showed up in 1970. Aside from the obvious yield advantage, a big factor in widespread acceptance of hybrids was the uniformity which facilitated efficient machine harvest. However this uniformity has a pitfall. If a field is planted to one variety of hybrid corn all of the plants in the field are genetically identical. Therefore if one plant is susceptible to a pest, all of the plants are susceptible. The dangers of this genetic vulnerability can be mitigated somewhat by planting different varieties of hybrid corn in a given area or even in the same field. However in the 1960s another factor contributed to the genetic vulnerability of hybrid corn. The process of hand removal of tassels of female parents proved to be time consuming and expensive. Finding high school youth willing to spend their summers trudging up and down corn rows in the heat of the summer in Illinois and Iowa became more and more difficult. When a breeding technique was developed which incorporated male-sterile cytoplasm into female parent lines it was quickly adopted by the seed companies. There was no longer any need to pay people to hand remove the tassels. Unfortunately there were only a few sources of male-sterile cytoplasm and by the late 1960s approximately 80% of the hybrid corn varieties were developed using a line known as Texas Male-Sterile Cytoplasm (T-Cytoplasm). In the crop production year of 1970 a perfect storm developed with the occurrence of a particularly virulent strain of the fungal disease Southern Corn Leaf Blight (SCLB), warm moist weather conditions that favored SCLB, and susceptibility to SCLB in all hybrid corn varieties developed using T-Cytoplasm. Many acres of corn production were lost as a result. “In August 1970, Illinois Secretary of Agriculture John W. Lewis was estimating that 25 percent of his state's corn crop was already lost to the blight. Just one year earlier, Illinois had been the nation's top corn producer, accounting for more than one-fifth of the crop.” http://www2.nau.edu/~bio372-c/class/sex/cornbl.htm

In the aftermath of the 1970 debacle the seed companies reverted to using hand removal of tassels until new lines of male-sterile cytoplasm were developed. But a hard lesson had been learned by corn farmers and they would never again have quite the same level of trust in hybrid corn as they did before 1970. Herbivore Reed

Next: Why there may be a place for open pollinated corn varieties

1 comment:

  1. Very interesting. Thanks. Someone just gave me hybrid corn seed so I was doing some research online and found this post.

    ReplyDelete

Comments with links to business websites will not be published.

Note: Only a member of this blog may post a comment.