Outlook for Transgenic Corn


Over 20 engineered crops are now being commercialized and quickly brought to market. Farmers have their choice of a list of herbicide-, insect-, and disease-resistant hybrids and varieties, and the numbers are certain to increase rapidly over the next several years with more crop introductions and "stacking" of multiple characteristics within crops. While transgenic seed introductions in the major field crops (corn, soybeans, cotton, and potatoes) have taken the early lead, specialty crops in fruits, vegetables, and forages are not far behind. Major agribusinesses such as Novartis, Monsanto, Dekalb, and Pioneer Hi-Bred International, are putting the full efforts of their research and marketing programs into engineered crops to ensure their success in the market place. Some of this information was obtained from an article in "AgConsultant" Magazine (Seed Scorecard, J. C. Sulecki and B. Kantz, 11/96, pp.4-7). The following is a description of what to expect with engineered corn over the next few years.


This first major enhanced technology, traditionally bred and introduced in 1991, allows for over-the-top spraying of imidazolinone (IMI) hybrids for control of annual grass and broadleaf weeds. Hybrids have either the T- or IT-Gene, which imparts resistance to Pursuit-based herbicides, (Contour and Resolve) and carryover levels of Scepter; or the IR-Gene, which provides resistance to Pursuit-and Scepter-based herbicides. About 3 million acres of IMI hybrids-available from most major corn seed companies-are expected to be planted in 1997.


Sethoxydim-resistant (SR) hybrids-formerly known as Poast Compatible-are traditionally bred for over-the-top applications of Poast, Poast Plus, and Headline, which provide economical control of such grasses as woolly cupgrass and johnsongrass. Contains a slightly altered gene in the resistant ACC'ase enzyme, which is essential for plant growth but is shut down by sethoxydim. For most weeds, Poast should be applied when the plant reaches 8 inches in height, although rescue treatment on 16-inch species can be effective for some wssds. About 700,000 to 1 million acres are expected to be planted to SR-Corn in 1997. Long-term, interest in the technology is expected to be especially high following years such as 1996 when bad spring weather in the Midwest prevented preemergence applications. DEKALB and BASF sold out of their SR-Corn in 1996.

Liberty Link Corn

Awaiting 1997 registration at this time, Liberty Link corn is genetically engineered for tolerance to over-the-top applications of the non-selective herbicide Liberty (glufosinate-ammonium). Benefits include a wide window of application and an alternative to ALS herbicides, which have shown some weed resistance in the Midwest. A resistance gene (PAT) detoxifies glufosinate and allows corn to give off ammonia and thrive while the non-PAT weeds around the crop shrivel and die. Depending on registration, an estimated 1 to 1.5 million acres could be planted in 1997. Virtually all major corn seed companies have the PAT gene (used as a "marker" gene in genetic engineering) and are planning introduction of Liberty Link hybrids.


Hybrids genetically engineered to carry the Bacillus thuringiensis (Bt) toxin provide season-long control of European corn borer (ECB). Bt corn produces a protein in green tissue and pollen; when young ECB larvae feed on just a small amount of tissue before they ingest enough of the protein to disrupt their gut lining, and soon cease feeding and die. About 6 million acres of Bt corn, introduced this year, will be planted in 1997 to hybrids available from Mycogen, Ciba Seeds, and Northrup King. A resistance management program using refugia is a must. Such programs currently involve monitoring ECB populations and planting Bt corn in blocks rather than strips to prevent insect migration. While the program may change in future years, Ciba Seeds now says refugia are not necessary because of Bt corn's relatively low percentage of the total corn acreage.

Other Corn Technologies

Roundup Ready Corn, due for introduction in 1998-99, could be very effective but a little more 'iffy' than RR-soybeans. Preliminary testing has shown that RR-corn may be more susceptible to herbicide injury. Hybrids traditionally bred for tolerance to soils with high pH are being targeted in the Western Corn Belt. Yields could be at least one-third higher than susceptible hybrids. Ongoing research at several seed companies is focused on developing hybrids with tolerance of or resistance to gray leaf spot (GLS), the Corn Belt's number one foliar disease. In the developmental stages are other Bt strains and genetically engineered modes of action to control such major pests as rootworms, black cutworms, armyworms, earworms, and sugarcane borers. "Identity preserved" or value-added hybrids, bred for certain desirable traits such as high-oil content, improved milling qualities, specific food characteristics, and enhanced animal nutrition, are the "sleeper" of enhanced seed systems. Many major seed companies expect to have full-blown programs by the turn of the century. Technologies will be "stacked" for multiple characteristics. Agriculture's first dual herbicide-resistant hybrid--resistant to both Liberty and IMI herbicides--is nearing completion and will be commercialized by ICI/Garst.

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