Corn & The Environment
Corn Breeding & Genetics

Corn has continuously been modified genetically by humans since it was first domesticated over 7000 years ago.

Teosinte, a grassy weed found in Central and South America, generally considered to be the wild species from which corn originated, bears limited resemblance to corn which is grown by farmers in any country.

Selection by native farmers resulted in gradual changes in the genetic makeup of corn, and this process was continued by immigrant European farmers who grew corn in the United States and adjacent areas of southern Canada.

Hybrid corn

A major change occurred in the 1930s and early 1940s when the use of hybrid corn became prevalent in southern Canada. The new hybrids were much higher yielding, more competitive with weed species, and much more tolerant of the European corn borer - an insect pest which wrecked havoc on corn fields in earlier years.

The introduction of hybrids meant that farmers were no longer able to use seed harvested from their own fields to plant the next year's crop (unless, of course, they were willing to accept the low yields and other problems associated with the use of "open-pollinated" corn varieties), and were obliged to buy new hybrid seed from seed companies each year.

This annual purchase of hybrid corn seed, in turn, financed a major investment in private corn breeding. As a result, yields of corn have generally increased at a faster rate (average of 1.7% per year from 1957-1988 in Ontario, Tollenaar et al., 1993) over the past 30-40 years, than those of other, non-hybrid crops. Major improvements have also been made in other traits such as standability (the ability to remain standing until time of harvest), early maturity (permitting hybrid corn to be grown in much cooler, shorter-season areas of Canada than was formerly the case), disease resistance, insect tolerance, grain quality, and the rate of pre-harvest grain drying (thereby reducing the cost of artificial drying after harvest).

Newer hybrids more stress tolerant

Newer hybrids are more tolerant of drought and shading. Indeed, newer hybrids are more tolerant of many stresses than were their predecessors, including the indigenous varieties grown centuries ago. These improvements include greater resistance or tolerance to weed competition, low fertility, shading and lodging (falling over before harvest) (Tollenaar et al., 1993).

Private corn breeding has been supported by public research at locations such as the University of Guelph and several research stations of Agriculture and Agri-Food Canada. Public research has been important in developing inbreds and broadly based breeding "populations" which can be used by commercial breeders for hybrid development. Public researchers have also helped private breeders in their search for greater pest resistance and/or tolerance, and in the improvement of grain quality, lodging resistance, and crop yield.

Genetic diversity

Major effort is being made, internationally, to preserve indigenous populations of corn for potential use in future breeding programs. Those who maintain these populations (this means growing plants and increasing seed supply from time to time, under conditions which ensure that these plants are not cross-fertilized with pollen from corn plants in adjacent fields) include universities, Agriculture Canada, the United States Department of Agriculture, the Centro Internacionale de Mais y Trigo (CIMMYT [link]) in Mexico, and most major private seed companies. An estimated 50,000 different types of corn exist in "genebanks" around the world (Chang, 1992). There are about 250 to 300 races of corn in existence (Brown and Goodman, 1977) of which only a few are used extensively for commercial production.

Biotechnology

Biotechnology offers the potential for further improvement in corn. Features which might be improved or added to corn, with potential for improvements in both farm income and environmental quality, include complete genetic resistance to insects such as the European corn borer and corn rootworm, nitrogen fixing ability, greater resistance to stalk and root rot disease organisms, tolerance to high and low temperatures, and faster rates of natural grain drying. Higher yield potential, with its associated benefit of increasing soil organic matter levels, remains an important breeding objective.