MU SOYBEAN GENE ZOO

Demonstration of soybean history from domestication to modern varieties

 

The wild progenitor of soybean is Glycine soja. Glycine soja can still be found in parts of China and other Asian countries. The plant is a vine that twines around other plants and structures for support. Leaflets are much smaller than those of modern soybean varieties. Glycine soja seeds are small, black, and hard.

 

Soybean was introduced in what would become the USA as early as 1765. The first varieties grown in the Midwest were introductions from China. The USDA began organized introductions of soybean varieties from China and other Asian nations in 1898. Two examples of early introductions from China into the Midwest are Mukden and Mandarin.

 

The primary purpose for soybean cultivation in the USA was hay and other forage uses until World War II. War with Japan and Japan’s control of oil palm production in SE Asia necessitated finding a new source for vegetable oil and soybean seeds came to the rescue. By 1944, nearly 75% of USA soybean acreage was harvested for grain.

 

Soybean introductions from China were used as parents of the first varieties developed in the USA. At first, nearly all soybean varieties were released by universities or the USDA. Now, private companies produce the majority of soybean varieties. The MU Soybean Gene Zoo displays one or more varieties released in each decade from the 1910s through the 2010s.

 

Demonstration of the use of biotech and non-biotech trait development

 

Soybean was one of the first major agricultural crops for which biotechnology was used. Varieties that contained a gene that made plants resistant to the herbicide glyphosate were commercialized in 1995. Today, soybean varieties may possess one or both biotechnology traits that confer resistance to herbicides. The glyphosate resistance trait (e.g. Roundup Ready® and Roundup Ready 2 Yield® came from a bacterium in the Agrobacterium genus. The glufosinate resistance trait (Liberty Link®) originated in the bacterium Streptomyces hygroscopius. Both of these traits allow for the post emergence application of a nonselective herbicide to soybean plants. STS® is a non-biotech trait that increases soybean plant tolerance to a class of herbicides called sulfonylurea.

 

Demonstration of maturity group adaptation

 

soyMAP small.jpgAlthough temperature affects soybean growth and development, soybean plants are also quite sensitive to photoperiod. The lengths of the light (photoperiod) and dark periods within a 24 hour day change each day. These changing photoperiods regulate the timing of flowering and other stages of soybean plant development. Soybean is classified as a short day plant because flower initiation is stimulated when photoperiod is shorter than a critical value. Critical values differ among varieties and are determined by a variety’s genes.

 

Photoperiod lengths differ among latitudes on any specific day. After the first day of spring and until the first day of fall, photoperiods are larger as latitude increases (further north). Because of soybean’s sensitivity to photoperiod, soybean varieties are assigned to one of 13 maturity groups. These maturity groups are adapted to relatively narrow bands of latitude. In North America, MG OOO is adapted to southern Canada; whereas, MG 10 (X) is adapted to Mexico and the Caribbean Islands.

 

Nearly all soybean varieties planted in Missouri are MG 3 (III), 4 (IV), or 5 (V). Varieties adapted to maturity groups earlier than 3 tend to produce short plants with less yield potential if planted in Missouri. Varieties adapted to maturity groups 6 and later tend to produce plants that are tall and often flower too late to produce yield if planted in Missouri. The MU Soybean Gene Zoo demonstrates the effects of maturity group adaptation on plant growth and yield potential. Varieties from MG 00 to 5.9 are on display.

 

Demonstration of special use soybean types

 

Soybean seeds are rich in both oil and protein. Nearly 90% of the oil is used for human food; whereas, the protein is most often used for animal feed. Some industrial products are made from either soy oil or protein.

 

Soybean oil contains five fatty acids: palmitic acid (11%), stearic acid (4%), oleic acid (22%), linoleic acid (55%), and linolenic acid (8%). Soybean varieties may differ slightly for the percentages of these fatty acids, and the fatty acid mix can be affected by environment. Modern breeding programs are addressing the fatty acid profile of soybean oil. Varieties with dramatically different proportions of fatty acid types are already available or soon will be available for contract production.

 

Palmitic and stearic acids are saturated, meaning that they contain no carbon to carbon double bonds. There is some evidence that consuming high amounts of saturated fatty acids has a negative impact on human health including heart disease. Although the amount of saturated fatty acids in soybean oil is lower than in animal products such as butter and lard it is higher than in some other plant oils such as canola. Decreasing saturated fatty acids content is a goal of some breeding programs.

 

Linoleic and linolenic acids are polyunsaturated, meaning that they contain more than one carbon to carbon double bonds. Linolenic acid contains three carbon to carbon double bonds and is not suitable for high temperature uses such as frying. It also reacts easily with oxygen, causing the oil to spoil, which shortens shelf life. Linolenic acid is the primary reason soybean oil must be hydrogenation. This process reduces the number of unsaturated bonds, but also leads to the formation of trans-fatty acids - a possible human health risk. Low linolenic varieties have less than 4% linolenic acid. This reduces the amount of hydrogenation needed and trans-fat formation.

 

The monounsaturated fatty acid, oleic acid, might have advantages for human health. Increasing the amount of oleic acid in soybean oil is a goal of some breeding programs.

 

Examples of two food uses of soybean are natto and tofu. Natto is a fermented product with high protein content. Fermentation is facilitated by the bacterium Bacillus natto. Natto has a sticky texture and strong odor and taste. Natto varieties are usually small seeded because this aids fermentation.

 

Tofu is made by coagulating soy milk followed by pressing the curds into blocks. Tofu can be used fresh or after further processing. Tofu has very little flavor or smell on its own and is often added to other foods. Tofu varieties usually produce large seeds with a clear hilum.

 

All soybean varieties are edible, but certain varieties are known as edamame. Edamame soybeans are harvested, usually by hand, before maturity. The seeds are left in the pod. Pods containing seeds are boiled and eaten. Edamame varieties are usually large seeded with milder taste than normal soybean varieties.

 

Demonstration of the effects single genes on plant growth, development, and morphology

 

Growth Habit


Soybean growth habit is controlled by genes at two loci. One locus determines whether the plant possesses the indeterminate (Dt1Dt1) or determinate (dt1dt1) growth habit. Plants with the indeterminate growth habit continue to produce leaves and stem growth for 25 to 40 days after flowering begins. This results in considerable overlap between vegetative (leaves and stems) growth and reproductive (flowers, pods, and seeds) growth. Plants with indeterminate growth habit often exhibit many different development stages of flowers and pods at nodes along the stems. Leaves located near the top of the plant are often smaller than leaves located near the middle of the plant.

 

On plants with the determinate growth habit, leaf and stem growth stops shortly after flowering begins. This results in a small overlap between vegetative growth and reproductive growth. Plants with determinate growth habit exhibit nearly uniform development stage of flowers and pods along the stem. Large leaves occur near the top of the plant, and the stem terminates in an often large raceme that produces a cluster of pods.

 

Growth habit is often related to Maturity Group. Varieties in MG000 through MGIV nearly always exhibit the indeterminate growth habit. Varieties in MGV through MGX nearly always have the determinate growth habit. Adding the Dt1 gene to variety adapted to Missouri greatly shortens the plants.

 

At a second locus, an allele (Dt2) causes plants to have a semi-determinate growth habit if combined with Dt1Dt1 at the other locus. Plants with this growth habit exhibit stem, leaf, and pod growth characteristics in between plants with indeterminate and determinate growth habits.

 

The MU Soybean Gene Zoo demonstrates indeterminate, determinate, and semi-determinate growth habits in a ‘Clark’ background. This means that all genes other than genes controlling growth habit are identical.

 

Morphology


The appearance of soybean plants can be dramatically changed by a single gene. Several of these are exhibited at the MU Soybean Gene Zoo. All traits are in the Clark background.

 

Non-nodulating plants do not produce nodules. Nodules form on roots and house nitrogen fixing bacteria. Plants without nodules often exhibit symptoms of nitrogen deficiency.

 

Chlorophyll deficient mutant reduces the production of the green pigment chlorophyll in leaves. Chlorophyll is required for photosynthesis. Leaves appear yellow or light green because of other pigments that would normally be masked by chlorophyll.

 

Glabrous pubescence results in stems and leaves with little or no pubescence. Pubescence are hair-like structures that protect soybean plants from feeding of insects with sucking mouth parts. Plants without pubescence often suffer from viruses that are transmitted by these insects. Dense pubescence results in stems and leaves with greater than normal amounts of pubescence.

 

Soybean leaves contain three leaflets (except the first pair of unifoliolate leaves). Mutant cause leaves to produce five or seven leaflets. Narrow leaflet results in leaflets that are much narrower than normal.

 

Sources of resistance to SCN


Soybean cyst nematode (SCN) is a small, soil-living, round worm that attacks soybean roots. SCN is one of the most destructive soybean pests and costs soybean farmers several billion dollars in lost yield each year. Fortunately, several genes that confer resistance to SCN have been found. These genes interfere with feeding and reproduction of the female nematode. But, resistance is not the same as immunity, and some damage and yield loss is possible even with planting of resistant varieties.

 

The first SCN resistant variety was released in 1966, about 12 years after SCN was discovered in the USA. The source of SCN resistance of this variety was Peking. Peking is a dark-seeded introduction from China. Few modern varieties have Peking as the sole source of SCN resistance, although it may be used in combination with other sources.

 

The most common source of SCN resistance comes from the plant introduction, PI88788. The first variety with this source was released in 1978. More than 95% of all SCN resistant varieties in the USA have PI88788 as the source of SCN resistance.

 

Another source of resistance that is used in some varieties is PI437654. This plant introduction was first used as a parent of ‘Hartwig’, and Hartwig was used in the development of a group of trademarked varieties - CystX. PI437654 is unusual in that it confers resistance to all known races of SCN.

 

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