Subcommittee A: Section 2 Genetic Diversity and Gene Banks by Andrew Lynch

Food crops were first domesticated from wild species nearly ten thousand years ago. Since then, farmers have continued to seek ways to improve the quality and yield of their crops. Through the use of selective breeding and cross pollination, farmers have been able to achieve these goals and attain significant improvements in crop harvests. However, at the same time, they have also hindered the possibility of future crop enhancement.

One of the major problems with selective breeding is its effect on the genetic diversity of plants. Modern plant-breeding methodologies create new varieties from existing species. However, the existing modern species are already genetically similar, so the resulting varieties are even more closely related to each other. Furthermore, while desirable plant varieties are utilized, plant species exhibiting low crop yield or unfavorable characteristics are discarded. As a result, over time, plant varieties have become increasingly similar and genetically variable species obsolete.

Although limiting genetic diversity may not seem like a significant problem now, its effects on the future could be catastrophic. By breeding plant varieties so closely related genetically, farmers are left defenseless against the possibility of epidemics. Perhaps the best example of this was the outbreak of the Southern corn leaf blight. The Southern corn leaf blight was a disease that first surfaced in 1970 and devastated corn crops. The problem arose due to a single gene, which although valuable in increasing sterility, was also associated with vulnerability to disease.

The primary solution to limited genetic diversity has been the establishment and maintenance of gene banks. Gene banks are collections of seeds from plants varieties that are closely related to crop plants. These gene banks preserve wild plant species, which are the only remaining means of sustaining long-term genetic progress. Although past attempts to extract desirable genes from gene banks have been largely unsuccessful, recent studies have demonstrated that these genes, in fact, can be utilized. New procedures, based on molecular linkage maps rather than plant phenotype, have proved highly beneficial. Furthermore, they have lead to the following important discovery about plant varieties:

"While the high-yielding line often does contain a great number of positive alleles at the loci associated with yield, there are almost always some loci for which the inferior parent contributes a superior allele."

The implication of this discovery is that plant varieties that exhibit low crop yield may be useful in creating a new species with high crop yields. In other words, although a species does not display a favorable trait, it may still have a recessive gene that could be useful in a new variety. This is because of the fact that many quantitative plant properties are determined by a combination of several genes, not just one.

With this understanding, scientist have been able to identify favorable genes and locate them with molecular maps and quantitative trait loci analysis. The results have been quite successful and have demonstrated the importance of maintaining gene banks.

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