Crop Insights: Selecting Corn Hybrids with Diverse Genetics to Increase Yields and Stability
By Michael Rupert and Steve Butzen
- Every hybrid has strengths and weaknesses that could make it a top-performing choice for a certain environment or year, but a lower performer in a different environment or year.
- Corn growers should spread their environmental risk by planting a genetically diverse lineup of hybrids adapted to the different types of conditions they would commonly expect from year-to-year.
- An extreme case of lack of genetic diversity resulting in severe crop losses was the use of T male sterile cytoplasm on about 80 percent of US corn acres during the early 1970's.
- Over the past 83 years, Pioneer has assembled the largest pool of elite corn germplasm in the world, and over the last two decades, implemented a step change to increase the number and diversity of its unique elite parent lines.
- While US seed law allows seed to be sold under a brand name, it also requires the seed corn tags or bags to identify the variety name. To spread risk, check the variety name on the tag to avoid planting the same hybrids from two different companies.
- The advantage of genetic diversity is demonstrated in the number of wins in the National Corn Yield Contest by a diverse list of Pioneer® brand hybrids.
- Key traits to consider when choosing a hybrid include: maturity, yield, drought tolerance, standability, pest resistance, drydown, grain quality and harvestability.
A corn hybrid's genetics determine its overall yield potential and the measure of that potential achieved in varying growing environments. Because hybrids differ in genetics and therefore in response to environmental pressures, selecting which hybrids to grow is likely the most important decision corn growers make each year. All crop management decisions made before or after hybrid selection are focused on maximizing or protecting the genetic potential of hybrids to produce high yields of marketable grain or silage.
Hybrid selection, perhaps more than any other management practice, can help growers manage their risks. Most risks and uncertainties are a result of each season's unique weather patterns and pest pressures, and are largely beyond the growers' control. Growers must therefore make the most of decisions and opportunities that can be controlled to help lower the risk of crop loss. Choosing a diverse lineup of locally adapted hybrids that vary in maturity and agronomic strengths is an excellent strategy to help manage weather- and pest-related risks.
This article will discuss "genetic diversity" in corn hybrids and explain how growers can choose diverse hybrids. It will also explain how the lack of diversity can lead to widespread performance problems, the success of Pioneer corn breeders in increasing genetic diversity in Pioneer® brand hybrids, and the role of genetic diversity in achieving contest-winning yields.
Selecting a Diverse Hybrid Lineup
Variations in weather and pest pressure. Yearly fluctuations in weather make it difficult to select a single hybrid that will have stable performance year after year, even on the same field or farm. Figure 1 shows the extreme year-to-year climate variability growers experienced from 2004 to 2008. Pest pressures also vary from year to year, usually due to environmental factors that may be favorable or unfavorable for pest development. These include weather patterns, crop residue levels, rotation, tillage, etc.
Mitigating weather and pest risks. Because every year brings different risks for crops, farmers attempt to mitigate risk against key agronomic challenges and during critical periods. By planting hybrids of differing maturities over a period that may last several weeks, corn growers help ensure that their entire crop will not be simultaneously affected by risk factors during germination, emergence, vegetative growth, flowering, grain fill, and even harvest. Experience shows that by spreading out crop development, at least part of the crop will be at a stage more likely to "weather" a dramatic environmental event.
Farmers also mitigate risk by choosing hybrids bred for resistance or tolerance to expected environmental and pest pressures. To assist customers in this process, Pioneer hybrids are rated for their ability to withstand the most prevalent risk and stress factors. "Agronomic traits" rated by Pioneer scientists include stress emergence, stalk strength, root strength, drought tolerance, brittle snap resistance, and resistance to common diseases and insects.
Figure 1. The Pioneer EnClass® system shows the diversity of growing environments classified over the last five years. These weather variations must be considered as well as hybrid strengths when selecting hybrids.
No "perfect" hybrids. Choosing hybrids with the right combination of high yield and defensive agronomic traits can be challenging. The corn plant only has a finite amount of energy to partition between different attributes. If a hybrid is developed for maximum yield, it has less energy remaining for stalk strength, root strength, disease resistance and other agronomic traits. The plant breeder and ultimately the grower must decide which combination of strengths in a particular hybrid will result in the highest, most consistent profits year after year. Because all the required strengths are rarely found in any one product, growers should focus on selecting a set of hybrids that contain all the attributes they need.
Lack of Diversity - A Lesson from History
A genetic diversity strategy is important to acquire a set of needed hybrid strengths and avoid a common hybrid weakness. The best example of a lack of genetic diversity resulting in a widespread problem was the southern corn leaf blight epidemic of the early 1970's. Use of the Texas male sterile cytoplasm, or "T cytoplasm" to eliminate detasseling of seed fields resulted in about 80 percent of US corn acres containing this genetic characteristic. When a new race of southern corn leaf blight developed, all hybrids with the T cytoplasm were susceptible. The widespread use of the cytoplasm created a uniformly susceptible host across all US corn-producing areas. This allowed the disease to spread rapidly with severe yield reductions on tens of millions of corn acres. As a consequence, the seed industry abandoned the use of T cytoplasm male sterile genetics.
In 1972 the scientific community weighed in on the factors leading to the southern corn leaf blight outbreak. A study reported by the National Academy of Sciences stated that corn became vulnerable because a common genetic characteristic existed such that "whatever made one plant susceptible made them all susceptible."¹
In a 1976 report, the USDA stated: "In the [1960s], it became clear that relatively few corn breeding parents were being used to produce the bulk of American hybrid corn varieties. This narrowness of germplasm set the stage for potential vulnerability to diseases, insects and other stresses. In early 1970, environmental conditions in southern and north-central corn-producing regions were favorable for easy disease establishment and spread among vast plantings of highly uniform varieties."²
Increased Use of Genetic Diversity in Pioneer Corn Breeding
Pioneer has endeavored to increase the genetic diversity of corn germplasm utilized in commercial hybrids, as Figure 2 demonstrates. This figure shows a dramatic increase in Pioneer's pool of unique proprietary parent lines developed after 1970 (2a and 2b), and step changes in diversity in the last two decades (2c and 2d).
Since the company's beginnings in 1926, Pioneer corn breeders have led the industry in introducing new genetics and mining all available corn germplasm for genes favoring higher yields and more agronomic stability. Beginning with the widespread adoption of hybrid corn in the 1940's, average US corn yields have increased almost two bushels per acre per year. Yield gains are attributable partly to genetic improvements and partly to the abilities of corn breeders to develop hybrids that capitalize on the concurrent advancements in farming technology. In addition to improvements in yield, Pioneer corn breeders have made significant gains in agronomic stability.
|Figure 2. Pioneer corn germplasm pool. Note that the number of Pioneer parent lines developed in the last decade (2000 to present) is greater than the number developed in its previous 75-year history.|
Genetic Diversity in Today's Marketplace
Unfortunately, today's seed corn marketplace does not lend itself easily to achieving genetic diversity. Because more seed companies license hybrids from a single source, there is a growing concentration of some germplasm resources. Similar genetics often appear from several companies, and fewer truly different, top-performing hybrids are available. As a consequence, growers often do not receive the genetic diversity they expect in their corn lineup. Some extension corn specialists have expressed concern that this trend is becoming a serious problem in the seed corn industry.
In spite of these challenges, resources are available to help growers in selecting diverse hybrid genetics. The Federal Seed Act stipulates that no commercial corn hybrid may be sold under two or more variety names. This US seed law also requires that seed corn tags or bags identify the unique variety name (even though it allows seed to also be sold under a brand name). Therefore, growers should carefully check the seed corn "bag tags" to avoid planting hybrids from two different companies that have the same variety name.
Figures 3 and 4 show where variety names can be found on a sampling of hybrid seed corn tags. Seed providers should be willing to help growers locate this information, as well as provide more details on the genetic diversity available in their company's product offerings. Planting a lineup of unique hybrids across a range of maturities is one of the best ways for growers to reduce risk in their operations.
|Figure 3. Checking variety names (B0000167 in this case) on bag tags of commercial hybrids is the only way to verify if products from different companies are the same or different.|
Genetic Diversity in Hybrids from Pioneer
Pioneer offers growers unequalled genetic diversity. The company's customers can be certain that each Pioneer® brand hybrid is different from other Pioneer hybrids and genetically different from those of competitive brands. The following points describe Pioneer's approach to providing genetically diverse hybrids to the marketplace:
|Figure 4. A grower was unaware he had actually purchased the very same hybrid from two different companies this year until he closely examined the bag tags. The variety, B0000168, is the same on both tags, even though the "brand" names (Dekalb® brand RX674VT3 and Crow's® brand 4354 VT3) are different.|
- Pioneer parent lines, corn hybrids and other crop varieties are specific to Pioneer and are proprietary. They cannot be used by other companies without Pioneer's consent.
- Pioneer develops its products from a unique genetic base that has been developed over the last 80 years and which continues to increase in diversity.
- Germplasm is at the heart of Pioneer's business and is key to the performance of its products.
- Growers have invested in Pioneer products with the understanding the company will continue to re-invest in the development of improved products. Pioneer's ability to continue that mutually beneficial process depends on the ability to protect the germplasm it has developed.
- Pioneer has initiated and maintains a scientifically proven testing program to help determine if misappropriation of Pioneer germplasm by its competitors has occurred.
- Pioneer supports the Federal Seed Act and is in compliance with all seed labeling regulations. Representing the same commercial hybrid as two or more different varieties is a violation of the Federal Seed Act, which serves to protect farmers and growers from this danger.
- Crops are always at risk from diseases, insects and weather. By providing hybrids with unique, diverse genetics and transparent seed bag labeling, Pioneer helps farmers manage the risks associated with any particular genotype.
- Without assurance of the differences between hybrids, growers do not have the ability to make good risk management choices.
- Local Pioneer sales professionals can help growers select a package of hybrids with diverse genetics and the right combination of traits for each particular field.
NCGA Yield Contest Shows Level of Diversity in Pioneer vs. Competitor Hybrids
The National Corn Growers Association (NCGA) sponsors a National Corn Yield Contest (NCYC) each year, recognizing first, second and third place winners in eight classes (nine classes prior to 2008). This contest is a proving ground and a showcase for top corn management practices, including hybrid selection and placement, soil fertility and pest management. The contest results reveal some interesting points about genetic diversity:
- In 2008, contestants using Pioneer® brand hybrids won 17 of 24 national awards (1st, 2nd or 3rd place) with 12 different hybrids (Figure 5 and Table 1). Contestants using Dekalb® brand hybrids won 6 awards with 3 different hybrids.
Figure 5. Seed corn brand planted by National Corn Yield Contest winners in 2005 - 2008.
- In 2007, contestants using Pioneer hybrids won 20 of 27 national awards, again with 12 different hybrids, while contestants using Dekalb® brand hybrids won 7 awards with 4 different hybrids.
- In both 2008 and 2007, the 12 Pioneer hybrids that won national awards were created using 12 unique female parents and 12 unique male parents (Table 1).
- Pioneer's nearest competitor had only 3 hybrid platforms that won contests in each of the past 2 years, illustrating the narrow genetic base used by much of the seed industry.
- In 2008, 6 Pioneer hybrids exceeded 300 bu/acre, and one of these exceeded it 3 times. This compares with one competitor hybrid exceeding 300 bu/acre.
- Over the past 10 years, Pioneer hybrids have won 226 out of 266 national awards in all the diverse growing conditions represented by NCYC entries.
Table 1. 2008 NCYC winning hybrids (all yields exceeding 300 bu/acre are shown after the hybrid number.)
|Pioneer® brand Hybrids||Dekalb® brand Hybrids|
|17 wins, 12 hybrids,12 platforms
12 male and 12 female parents
|6 wins, 3 hybrids, 3 platforms|
|H31D61 (362 bu/acre)||DKC52-59ybrid|
|H31N30 (327, 347, 368 bu/acre)||DKC61-69 (316 bu/acre)|
|32B11 (331 bu/acre)|
|34A14 (317 bu/acre)|
|35F40 (321 bu/acre)|
These results illustrate the extensive genetic diversity available in Pioneer's elite hybrid lineup compared to that of its competitors. They also demonstrate that top yields can be achieved in many hybrid maturities and genetic backgrounds when products are properly matched to their growing environment. This approach of providing the right product for the right acre that produces winning entries in the National Corn Yield Contest also produces a diverse hybrid lineup to help growers maximize farm yields and reduce risk.
Stable, high yields from season-to-season are critical for maintaining a profitable farming operation. With that in mind, corn growers should spread their environmental risk by planting a genetically diverse lineup of high-yielding, locally adapted hybrids that vary in maturity and agronomic strengths. Pioneer realizes the importance of genetic diversity to the success of corn growers and the stability of the corn industry. Therefore, the company focuses its efforts to utilize fully the genetic diversity of corn to maximize yields and agronomic traits. Recent advances in technologies are allowing Pioneer researchers to raise yields and agronomics to unprecedented levels by leveraging an industry-leading corn germplasm pool.
References and Resources
¹National Research Council. 1972. Genetic Vulnerability of Major Crops. National Academy of Sciences. Washington, D.C.
Selecting High-Yielding Hybrids - What NCYC Winners Can Teach Us
Hybrids tested against each other in a single environment (e.g., a university or seed company test plot) routinely vary in yield by at least 30 to 40 bu/acre. At contest yield levels, hybrid differences are even higher. That is why selecting the right hybrid is probably the most important decision contest winners and all corn growers can make.
The genetic potential of many hybrids now exceeds 300 bu/acre. But realizing that yield potential requires matching hybrid characteristics with field attributes such as moisture- supplying capacity, insect and disease spectrum, maturity zone, residue cover and even seedbed temperature. Generally, contest participants should select a hybrid with:
- Top-end yield potential. Growers should examine yield data from multiple, diverse environments to identify hybrids with highest yield potential for contest plots.
- Full maturity for the field. Using all of the available growing season is a good strategy for maximizing yield.
- Good emergence under stress. This helps ensure full stands and allows earlier planting, which moves pollination earlier to minimize stress during this critical period.
- Above-average drought tolerance to provide insurance against periods of drought that most fields experience.
- Resistance to local diseases. Leaf, stalk, and ear diseases disrupt normal plant function, divert plant energy, and reduce standability and yield.
- Traits for resistance to major insects such as corn borer, corn rootworm, black cutworm, and western bean cutworm. Insect pests reduce yield by decreasing stands, disrupting plant function, allowing diseases, feeding on kernels, and increasing lodging and dropped ears.
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