The Biology of Glycine max (L.) Merr. (Soybean)
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Biology document BIO2021-01: A companion document to Directive 94-08 (Dir94-08), Assessment Criteria for Determining Environmental Safety of Plant with Novel Traits.
This document replaces BIO1996-10 [The Biology of Glycine max (L.) Merr. (Soybean)].
On this page
- 1. General administrative information
- 2. Identity
- 3. Geographical distribution
- 4. Biology
- 4.1 Reproductive biology
- 4.2 Breeding and seed production
- 4.3 Cultivation and use as a crop
- 4.4 Gene flow during commercial seed and biomass production
- 4.5 Cultivated soybean as a volunteer weed
- 4.6 Means of movement and dispersal
- 5. Related species of soybean
- 6. Potential interaction of soybean with other life forms
- 7. References
1. General administrative information
The Canadian Food Inspection Agency's Plant and Biotechnology Risk Assessment (PBRA) unit is responsible for assessing the potential risk to the environment from the release of plants with novel traits (PNTs) into the Canadian environment.
Risk assessments conducted by the PBRA unit require biological information about the plant species being assessed. Therefore, these assessments can be done in conjunction with species-specific biology documents that provide the necessary biological information. When a PNT is assessed, these biology documents serve as companion documents to Directive 94-08 (Dir 94-08): Assessment Criteria for Determining Environmental Safety of Plants With Novel Traits.
This document is intended to provide background information on the biology of Glycine max, including
- its identity
- geographical distribution
- reproductive biology
- related species
- the potential for gene introgression from G. max into relatives
- details of the life forms with which it has the potential to interact
Such information will be used during risk assessments conducted by the PBRA unit. Specifically, it may be used to characterize the potential risk from the release of the plant into the Canadian environment with regard to
- gene flow
- plant pest properties
- impacts on other organisms
- impact on biodiversity
Glycine max (L.) MerrillFootnote 1
Fabaceae (Leguminosae) family, commonly known as the legume and pea familyFootnote 1, Footnote 2.
Synonyms for G. max includeFootnote 1, Footnote 2, Footnote 3
- Dolichos soja L.
- Glycine angustifolia Miq.
- Glycine gracilis Skvortsov
- Glycine hispida (Moench) Maxim.
- Glycine hispida var. brunnea Skvortsov.
- Glycine hispida var. hispida (Moench) Maxim.
- Glycine hispida var. lutea Skvortsov
- Glycine max subsp. max (L.) Merr.
- Glycine soja (L.) Merr.
- Glycine ussuriensis Regel & Maack
- Phaseolus max L.
- Soja angustifolia Miq.
- Soja hispida Moench
- Soja japonica Savi.
- Soja max (L.) Piper
- Soja soja H. Karst
- Soja viridis Savi.
Some synonyms of G. max require special note: first, in this document Glycine gracilis Skvortsov is considered synonymous with G. maxFootnote 4, Footnote 5 but this taxonomic treatment is debated and not universally appliedFootnote 6, Footnote 7, Footnote 8. Second, Glycine soja (L.) Merr., a synonym of G. max, should not be confused with G. soja Siebold & Zucc. (2n=40) the other member of the Soja subgenusFootnote 1.
2.4 Common names
G. max is known asFootnote 1, Footnote 2
- reseeding soybean
- wild soybean
2.5 Taxonomy and genetics
The genus Glycine is a member of the tribe Phaseoleae of the legume and pea family Fabaceae / LeguminosaeFootnote 1. Phaseoleae comprises approximately 29 genera and contains agronomically-important species, includingFootnote 1
- cowpea (Vigna unguiculata)
- Bambara groundnut (Vigna subterranea)
- ground-bean (Macrotyloma geocarpum)
- mung-bean (Vigna radiata)
- bean (Phaseolus vulgaris)
- pigeon-pea (Cajanus cajan)
The genus Glycine is divided into the subgenera Glycine and SojaFootnote 1; the genus was last revised by HermannFootnote 5. G. max belongs to the subgenus Soja, which also contains G. soja Siebold & Zucc., a wild species of soybean that grows in many Asian countries. The Glycine subgenus contains approximately 26 wild perennial speciesFootnote 1.
G. max is a paleopolyploid, (2n=40)Footnote 9.
|Taxon||Scientific name and common name|
|Subkingdom||Tracheobionta (vascular plants)|
|Superdivision||Spermatophyta (seed plants)|
|Division||Magnoliophyta (flowering plants)|
|Family||Fabaceae / Leguminosae (legume and pea family)|
|Genus||Glycine Willd. (soybean)|
|Species||Glycine max (L.) Merr. (soybean)|
2.6 General description
Cultivated soybean is an erect, bushy herbaceous annual that can grow up to 1.5 metres (m) tallFootnote 10. Soybean varieties are adapted to a range of geographic and climatic regionsFootnote 11. The main growth habits (also referred to as stem types) of soybean are: determinate, semi-determinate and indeterminate. Determinate varieties, characterized by vegetative growth that is nearly complete when the plant starts flowering, are primarily grown in the southern United StatesFootnote 11. Most soybean varieties grown in Canada are indeterminate, characterized by vegetative and reproductive development co-occurring after reproductive growth beginsFootnote 12.
Soybean varieties are classified into 13 maturity groups (MGs) based generally on latitudeFootnote 13. The rate of plant development is influenced by photoperiod and temperatureFootnote 14. MGs vary from 000 for the earliest maturing varieties to X for the latest maturing varieties. Early maturing varieties (MG 000 to MG III) are most suited to the Canadian climateFootnote 15.
Soybean plants have a deep taproot and a large number of secondary roots that support many smaller rootsFootnote 16. Multibranched adventitious roots emerge from the lower portion of the hypocotyl. While the taproot may reach a depth of 2 m and the side roots a length of 2.5 m, under typical field conditions, the root system is less extensive and mostly in the top 15 centimetres (cm) of the soilFootnote 16, Footnote 17. Bacterial root nodules form with the gram-negative bacteria Bradyrhizobium japonicum and may extend to depths of at least 1 metreFootnote 18. The number of bacterial nodules per plant varies; Grubinger et al.Footnote 18 reported a range from 21 to 128 nodules per plant in 8 different varieties tested at 1 site.
Fine trichomes occur on the leaves, stems, sepals and pods. Soybean plants have 4 types of leaves: simple cotyledons or seed leaves, primary leaves, foliage leaves and prophylls. The pair of cotyledons occur first and are oppositely arranged. The 2 primary leaves are unifoliate, occurring opposite each other at the node above the cotyledons. Subsequent foliage leaves are trifoliolate, and are on alternate sides along the stem. Compound leaves with 4 or more leaflets are occasionally present. The prophyll occurs as small pairs of simple leaves, found at the base of lateral branches and the lower part of the pedicel of each flowerFootnote 11.
3. Geographical distribution
3.1 Origin and history of introduction
Historical and geographical evidence suggests that soybean was domesticated in China 4,000 to 9,000 years agoFootnote 6, Footnote 19. Soybean has 20 chromosome pairs derived from 2 rounds of genome-wide duplicationFootnote 9. G. soja, a legume native to central China, is believed to be the progenitor of cultivated soybeans according to morphological, cytological and biochemical studiesFootnote 6, Footnote 20, Footnote 21. Comparative studies on the traits of wild, semi-wild and cultivated soybeans describe increases in the seed size, pod size, reproductive period and leaf area, and decreases in the number of seeds per plant, plant height and branchingFootnote 11. Research into the specific domestication events, including whether soybean evolved directly from G. soja or a G. soja/G. max complex, which diverged from a common ancestor about 0.27 million years ago, is ongoingFootnote 20, Footnote 22. Sedivy et al.Footnote 19 summarize research into the domestication of soybean, including the results of newly available molecular approaches.
Soybean was introduced in Europe by the 1700s, North America in 1765Footnote 23, and Central and South America in the mid-1900sFootnote 24. The earliest cultivation records in Canada are from 1893, introduced by Professor Charles Zavitz from the Ontario Agricultural College (Istvan Rajcan, personal communication). Soybean production began in Ontario as a hay crop, transitioning to a commercial oilseed crop after World War II disrupted trade routes. The proportion of Canadian cropland seeded to soybean increased consistently between 1961 and 2016, from 0.4% to 5.9% of Canada's total field cropland. In the mid-1970s, soybean varieties with earlier maturity and improved tolerance of colder climates were developed. These new varieties were not widely adopted until the mid-1990s when soybean production began in other provinces, namely Quebec and ManitobaFootnote 25.
3.2 Native range
Soybean is thought to have originated in eastern AsiaFootnote 1.
3.3 Introduced range
Soybean is grown worldwide. The following 20 countries were the highest soybean producing countries in 2018Footnote 26.
Asia China, India, Indonesia
Africa Nigeria, South Africa, Zambia
North America Canada, Mexico, United States of America
South America Argentina, Bolivia, Brazil, Paraguay, Uruguay
Europe France, Italy, Romania, Russian Federation, Serbia, Ukraine
3.4 Potential range in North America
Soybean has a wide potential distribution in Canada that includes all provinces and may continue to expand northward as temperatures increase and new soybean varieties are produced. Soybeans are grown in every province in Canada, with Ontario, Manitoba and Quebec producing approximately 50%, 29% and 16% of the total yield, respectivelyFootnote 27. Soybeans are widely cultivated in the United States. Illinois, Iowa, Minnesota, and Indiana were the highest soybean-producing states reported in the 2017 Census of AgricultureFootnote 28. No cultivation was reported in Oregon, New Hampshire, Idaho and HawaiiFootnote 28.
Soybean is a moderately salt-tolerant crop; the reported salinity threshold is about 5 deciSiemens per metre, but the effect depends on the exposure timing, soybean variety and environmentFootnote 29. Although soybean is considered a warm-season crop, its cultivation extends from the tropics to at least 52 degree latitude north, usually at altitudes of under 1,000 mFootnote 17. Soybean plants are sensitive to photoperiod and light quantityFootnote 17. Water requirements vary significantly, but generally soybeans require 330 to 825 millimetres of rainfall over the growing season to produce a good cropFootnote 17, Footnote 30. Water requirements are highest from flowering to seed filling. Soybeans may be affected by waterlogging and droughtFootnote 11. Dry conditions, especially in July and August, can result in green soybean seed at harvest, even when the seed moisture is below 13%Footnote 15.
Soybeans grow best in neutral or slightly acidic soil, and can tolerate a pH range of approximately 5.5 to 7.8Footnote 4. Soybean cultivation occurs on a broad range of well-drained soil types, though clay loam soils are optimalFootnote 17. While heavy clay soils present challenges for seeding and plant emergence after germination, soybeans perform adequately once established. Sandy or gravelly soils leave plants prone to drought stress, and are least suited for soybean production.
Soybeans are typically grown where growing-season temperatures are 10 to 40 degrees Celsius (°C)Footnote 11. Soybean seeds require soil temperatures of at least 10°C for germination and root nodulationFootnote 11. A root zone temperature of at least 15°C to 17°C is needed for adequate soybean nodulation and nitrogen fixation, while 25°C is optimal. Cold temperatures can affect soybeans throughout the season. In early spring, soybeans can tolerate -2.8°C for a short period before sustaining tissue damage. A severe frost during flowering or pod fill can reduce yield by up to 80%. During flowering, sustained temperatures of less than 10°C affect pollen formation and can result in parthenocarpic seed pods. Freezing during pod fill will result in severely damaged beans with a greenish, wrinkled seed coat. Yield reductions from late-season frost injury are smaller as the crop matures. Frost during the R5 stage reduces yield by 50% to 70%. Frost at the R6 stage will cause losses of 20% to 30%. Once the crop reaches the R7 stage only a 5% to 10% yield loss is expected. No yield reductions occur once the plants have reached physiological maturityFootnote 15.
Generally, soybeans are incapable of sustained reproduction outside of domestic cultivation and is non-invasive of natural habitats, although they can occasionally volunteer in cultivated crops or grow in unmanaged fields or disturbed habitats (for example, roadsides, areas around grain elevators, fallow fields)Footnote 5, Footnote 30, Footnote 31.
4.1 Reproductive biology
Soybean development is grouped into vegetative growth (leaves and nodes) and reproductive growth (flowers, pods and seeds)Footnote 11, Footnote 15. The reproductive biology of soybean is described by Fageria et al.Footnote 17, SinghFootnote 11, and it is summarized below.
Flowering usually begins 25 to 50 days after planting, and lasts 20 to 40 days. The flowering of early-maturing soybeans is mainly controlled by accumulated heat units, whereas later-maturing soybean varieties are primarily influenced by day length. When planted at the optimal time, soybeans will develop 4 to 7 trifoliolate leaves before the flowering period (anthesis) beginsFootnote 15. Flower clusters appear on a node of the stem. The first node with a flower cluster is on the fifth or sixth node. Depending upon growth habit – determinate or indeterminate – flower buds can form on the terminal or auxiliary racemes. The inflorescence, called a raceme, initially contains about 3 to 35 single flower buds. Up to 90% flower abortion is reported, leaving only a few flowers per node. Flowers consist of
- a tubular calyx of 5 sepals
- a corolla of 5 petals (1 banner, 2 wings, and 2 keels)
- 1 pistil
- 9 fused stamens with a single separate posterior stamen
Anthesis begins once the pollen has matured. The anthers mature in the bud and directly pollinate the stigma of the same flower (self-pollination)Footnote 32. The stigma is receptive to pollen approximately 24 hours before anthesis and remains receptive 48 hours after anthesis. Cross-pollination in plants at 10 m or more from the source pollen is absent or very rareFootnote 33, Footnote 34, Footnote 35.
Pollen tubes travel through the style and enter into the filiform apparatus: the pollen tube tip bursts and releases 2 sperm nuclei. One sperm nucleus fuses with the egg and forms a zygote, while the second sperm nucleus unites with the secondary nucleus, forming an endosperm. The inflorescence of each node may develop into 1 to 20 pods, resulting in up to 400 pods per plant. Pods are generally visible 4 to 14 days after the start of flowering, and reach their maximum length after 15 to 20 daysFootnote 36. The pod is straight or slightly curved, varies in length from 2 to 7 cm, and consists of 2 halves of a single carpel joined by a dorsal and ventral suture. As the plant reaches maturity, pods commonly change from green to yellow to brownFootnote 37.
Mature seeds develop from 30 to 50 days after fertilization. At maturity, pods usually contain 2 to 3 seeds but may contain up to 5. The seed, oval or spherical, consists of a seed coat surrounding a large embryo. Mature seeds of common varieties are normally yellow; however, they may be green, brown, black, or bicolorFootnote 38. The seed coat has a hilum that can vary in shape and colour based on plant genetics, environment and diseasesFootnote 12. The hilum colour can be yellow, black, brown, grey, or buffFootnote 15.
4.2 Breeding and seed production
Goals of soybean breeding in Canada include developing varieties with higher yield potential, increased abiotic stress tolerance, and pest and disease resistance, in particular resistance to
- Sclerotinia stem rotFootnote 39
- Phytophthora rotFootnote 40
- Rhizoctonia root rotFootnote 41
- soybean cyst nematodeFootnote 42
Other goals include improved nutrition (for example, increased vitamin E, modified fatty acid profile, isoflavone levels)Footnote 43, Footnote 44 and increased oil content for industrial usesFootnote 11. Research to develop a commercial hybrid soybean seed with increased yield, similar to hybrid vigour seen in crops like corn (Zea mays), is challenging and ongoingFootnote 24.
The genetic base of North American soybean cultivars is narrow and breeding programs have been largely divided into northern and southern cultivarsFootnote 45, Footnote 46. For the northern genetic base, 10 ancestral cultivars account for 80% of the genes presentFootnote 46. About 170,000 G. max accessions are stored in 70 countries with the largest collections in China and the United StatesFootnote 1, Footnote 24. Significant local adaptation is needed to incorporate available breeding material into suitable varietiesFootnote 11. These accessions vary significantly in agronomic characteristics including
- days to flowering (22 to 78 days)
- days to maturity (68 to 140 days)
- oil content (13.0 to 24.7%)
- response to environmental stressors
G. soja is the sole member of the primary gene pool for soybean (in other words, the only species that can cross with soybean and produce F1 hybrids with some fertility). G. soja has been evaluated in soybean breeding programs to improve traits including seed sizeFootnote 47, oil profileFootnote 48, soybean cyst nematode toleranceFootnote 42 and yieldFootnote 49. Wild perennial species in the genus Glycine are of interest to soybean breeders, but transferring traits into soybean has not been widely accomplished due to interspecific crossing barriersFootnote 50. The perennial relative G. tomentella has soybean rust resistance genes that confer higher tolerance than genes in current soybean varieties. Patzoldt et al.Footnote 51 discussed incorporating these genes into commercial soybean varieties.
Oilseed soybean is subject to variety registration in Canada under the authority of the Seeds Act and Seed Regulations (Part III and Schedule III)Footnote 52. Varietal purity standards for pedigreed seed crop production of Foundation, Registered and Certified seed are developedFootnote 53. As of 2020, there were about 1,600 soybean varieties with a national registrationFootnote 54.
Soybean breeding follows the common procedures for varietal development like other self-pollinating crops, similar to wheat and riceFootnote 24. Conventional breeding is based on the phenotypic selection of superior individuals from segregating populations. The most common breeding method used by soybean breeders is Single Seed Descent. It takes about 8 to 10 years to complete a breeding cycle, starting with making crosses to the release of variety or germplasmFootnote 24. Yield progress of short-season soybean in Canada has been approximately 0.5 to 1% per year from the early 1930s to 2000Footnote 55, Footnote 56. Newer cultivars have a greater number of seeds per plant, not greater seed sizeFootnote 55. A decrease in lodging, an increased tolerance to plant population stress, a reduction in seed protein, and an increase in seed oil have been incrementally occurringFootnote 56, Footnote 57, Footnote 58. The increase in seed yield is correlated with an increase in leaf photosynthetic and stomatal conductance rates, and a decrease in leaf area indexFootnote 59.
Molecular plant breeding tools have allowed for progress in soybean breeding, notably for quantitative traits such as yield, and abiotic and biotic stress tolerance. The sequencing of the soybean genome has aided efforts to link phenotypic effects with the causal DNAFootnote 9. After a target gene or quantitative trait locus (QTL) of interest to breeding goals is identified, marker-assisted selection can be used to select plants with the QTL of interest, even before plants are grownFootnote 24.
Modern biotechnology has been used to introduce novel traits into soybean including tolerance to herbicides and insect pests, and a modified fatty acid profile. Herbicide tolerant soybean was first authorized for unconfined release in Canada in 1999Footnote 60. Modifications include the introduction of the
- gm-hra gene encoding a modified ALS enzyme and conveying tolerance to the ALS-inhibiting herbicides
- phosphinothricin acetyltransferase pat gene conveying glufosinate-ammonium tolerance
- csr1-2 gene that encodes an Arabidopsis thaliana acetohydroxyacid synthase (AtAHAS) enzyme conveying tolerance to imazamox
- aryloxyalkanoate dioxygenase-12 (aad-12) gene conveying tolerance to 2,4-D
- gat4601 gene encoding a glyphosate N-acetyltransferase (GAT) enzyme conveying tolerance to glyphosate
- dicamba mono-oxygenase (dmo) gene conveying tolerance to dicambaFootnote 60
Soybean has also been modified to express insecticidal proteins derived from the soil bacterium Bacillus thuringiensis (Bt), including cry1A.105, cry2Ab2, cry1Ac, and cry1FFootnote 60. Target pests include the lepidopteran species corn earworm (Helicoverpa zea) and secondary pests from the genus Spodoptera (for example, fall armyworm, S. frugiperda). Most of the target pests for currently developed Bt soybean events have limited presence in Canada and do not overwinter, thus, Bt soybean has not been commercially planted in Canada.
4.3 Cultivation and use as a crop
Globally, 363 million tons of soybean were produced in 2018; Canada was the seventh-highest producing country harvesting over 7.3 million tonsFootnote 26. Ontario, Manitoba and Quebec are the top soybean producing provincesFootnote 27. In 2015-2016, 64% of Canadian soybean production was exported, mostly as non-processed whole grainsFootnote 25. In 2019, genetically modified soybean was planted on 68% and 75% of the total soybean acres in Quebec and Ontario, respectivelyFootnote 61.
Soybean crop management has intensified and is almost entirely mechanized in CanadaFootnote 11. Recommendations and information on soybean cultivation are well established and are published by the Ontario Ministry of Agriculture Food and Rural Affairs (OMAFRA)Footnote 15. This document focuses on grain soybean. Specific crop management practices and breeding considerations for vegetable soybean, commonly used in fresh soybean products for human consumption, are discussed in Chapter 19 of SinghFootnote 11.
Soybeans are very responsive to crop rotationFootnote 15 and a variety of crops and practices are used globallyFootnote 11. In Canada, common rotations include corn-soybean, winter wheat-soybean, and winter wheat-soybean-cornFootnote 62. In western Canada, rotations may include canola, for example wheat-canola-corn-soybean or canola-soybeanFootnote 63. Producers in the southernmost regions of Ontario may grow soybeans immediately following the harvest of their winter cereal or pea cropFootnote 15. Soybeans may be used in intercropping systems with crops including sunflower, corn and sorghum, though this practice is not common in CanadaFootnote 11, Footnote 64. In Ontario, approximately two-thirds of the soybean crop is grown with no-till or reduced tillage systemsFootnote 62.
Soybeans are planted based on the calendar date, soil temperature, short-term weather forecast and growers' preference. Planting too early or too late can drastically reduce yieldFootnote 11. Soybeans can yield well over a wide range of seeding rates. The optimal seeding rate depends on the seed size, plant type and maturity period of the genotypeFootnote 11. A typical emergence rate is 75 to 80%Footnote 15. Full yield potential is achieved in Ontario with final stands of 125,000 to 150,000 plants per acre, depending on row widthFootnote 15. In Manitoba, the recommended final stand is 140,000 to 160,000 plants per acreFootnote 65. If the plant stand establishment is not adequate, for example due to fungal infection, frost, hail, or herbicide injury, the stand may be replanted, patched, or thickenedFootnote 15. Soybeans grow well under a wide range of row widths. The choice of row width depends on
- the tillage system
- available equipment
- weed populations
- soil conditions
- disease pressure
- planting date
In Ontario, an intermediate row width of 38 cm may result in the higher yield potential associated with narrow rows and the reduced white mold associated with wide rowsFootnote 15.
Recommended seeding depth varies from 2.5 to 5 cmFootnote 11; guidelines in Ontario state 3.8 cm is generally adequate, but if planting early in the growing season using no-till practices into soil with adequate moisture, soybean seeds can be planted at 2.5 cmFootnote 15. After planting, fields may be rolled to help conserve soil moisture and improve field conditions for harvestFootnote 15. Light tillage may be used to break up the soil crust in cases where it is likely to inhibit soybean emergenceFootnote 15.
The bacteria Bradyrhizobium japonicum is needed for soybeans to establish nodulated root systems, allowing the plant to fix atmospheric nitrogen. Once soybeans have been grown with good nodulation, B. japonicum will survive in the soil, and it may be possible to grow future crops without further inoculationFootnote 65. Inoculation is recommended in areas where soybean has not been grown, or in acidic soils (below pH 6), sandy soils, or soils that have poor drainage and/or have been flooded for an extended timeFootnote 15. When establishing B. japonicum in a field, using 2 formulations or placements is recommendedFootnote 65. Liquid inoculants are placed on-seed and/or in-furrow, and granular inoculants that may use a sterile peat-based carrier are placed in-furrow with the seedFootnote 15. Soybeans can meet most of their nitrogen requirements through biological nitrogen fixation, reducing the need for chemical fertilizersFootnote 11, Footnote 65. The amount of nitrogen fixation is difficult to quantify and varies based on factors including the
- soil characteristics
- variety of soybean
- crop management
- bacterial strain presentFootnote 11
Soybean seeds germinate when the soil temperature reaches approximately 10°C, and cotyledons emerge 5 to 7 days after seeding under favourable conditions. Soybean plants that have developed beyond the cotyledons can tolerate temperatures as low as -2.8°C for a short time but can be killed by a hard spring frostFootnote 15. After mild frost damage, soybean plants may develop new shootsFootnote 15. Delayed planting is an approach to manage the risk of frost damage in soybean; however, this also reduces the yieldFootnote 15.
Manganese deficiency is the only micronutrient deficiency diagnosed in Ontario soybeans, it manifests as pale-green (slight deficiency) to almost white (severe deficiency) upper leaves with green veinsFootnote 15. Other micronutrient deficiencies are rare in Canada but can occur depending on local soil conditions. For example, some environmental conditions can reduce the availability and uptake of iron by the soybean plant, leading to iron deficiency chlorosisFootnote 65. Identifying high-risk fields in advance and variety selection are the best options to manage iron deficiency chlorosis.
The critical weed-free period for soybean is from the first to third trifoliolate-leaf stages (V1-V3)Footnote 15. Weeds affecting soybean crops in Ontario include annual grasses, for example
- barnyard grass (Echinochloa spp.)
- crabgrass (Digitaria sanguinalis)
- fall panicum (Panicum dichotomiflorum)
- witchgrass (Panicum capillare)Footnote 66
Annual broadleaf weeds of soybean include
- wild buckwheat (Polvgonum convolvulus)
- cocklebur (Xanthium strumarium)
- Canada fleabane (Conyza canadensis)
- lady's thumb (Persicaria maculosa)
- lamb's-quarters (Chenopodium album)
- common ragweed (Ambrosia artemisiifolia)
- giant ragweed (Ambrosia trifida)
- velvetleaf (Abutilon theophrasti)Footnote 66
Perennial weeds of soybean include
- field bindweed (Convolvulus arvensis)
- horsetail (Equisetum arvense)
- milkweed (Asclepias spp.)
- nutsedge (Cyperus rotundus)
- Canada thistle (Cirsium arvense)Footnote 66
A wide range of herbicides are used for weed control in soybean, with a broader spectrum of control achieved through the combination of herbicidesFootnote 66.
To dry the crop, desiccants may be applied when 80 to 90% leaf loss has occurred, and 80% of pods are yellowFootnote 65, although this is not a usual practice. Soybeans are usually direct combined, preferably with a combine equipped with a floating flexible cutter bar and automatic header height controlFootnote 15. Soybeans may also be swathedFootnote 65. Soybeans can be harvested when moisture levels are under 20%, but they must be stored at 14% moisture or lowerFootnote 15. Harvest losses and mechanical damage may be high when soybeans are harvested below 12% moistureFootnote 15. A variety of drying methods can reduce moisture to 14% or lower, which is required for storageFootnote 15.
Soybean is cultivated worldwide and is consumed as a food and animal feed. Soybean has become the primary source of edible fats and oil in North AmericaFootnote 25. After edible oil extraction, the resulting 'soybean meal' is a high protein ingredient in animal feedFootnote 11. Soybean may be eaten in fermented form or incorporated into products after being dried and ground. Soybean is processed and used in products such as
- soy milk
- isolated soy protein
- concentrated soy proteinFootnote 11
Soybean oil is also used for the production of printing ink and biodieselFootnote 11.
Insect pests and diseases affecting soybean are discussed in Section 6. A Field Crop Protection Guide is published yearly by OMAFRA, recommending federally registered insecticides and fungicides for use in soybean cropsFootnote 62.
4.4 Gene flow during commercial seed and biomass production
Soybean is self-pollinatedFootnote 32. Natural cross-pollination to neighboring plants is typically below 1%, but higher values have been observedFootnote 67. The cross-pollination rate is influenced by
- the distance between plants
- soybean genotypes
- the environment
- flowering synchrony
- the insects presentFootnote 67, Footnote 68, Footnote 69
Cross-pollination of soybean plants that are more than 10 m from the source pollen is absent or very rareFootnote 33, Footnote 34, Footnote 35. Insects are believed to be responsible for some cross-pollinationFootnote 68, Footnote 70. Flowers can be a source of nectar and pollen for many insects including
- honey bees, Apis mellifera L. (Hymenoptera: Apidae)
- wild social and solitary bees (Hymenoptera: Apoidea)
- flower-visiting flies (Diptera)
- thrips (Thysanoptera: Thripidae)
As they feed, insects may transfer pollen between soybean flowers. Soybean plants release very little airborne pollen, which does not travel long distancesFootnote 33, Footnote 71. Wind dispersal is expected to be negligible.
In Canada, the production of soybean seeds grown for pedigreed status must meet standards specified by the Canadian Seed Growers' AssociationFootnote 53. For Foundation, Registered, and Certified production, soybean must be planted at least 3 m from different varieties of soybean or non-pedigreed soybean. To multiply breeder seed, the isolation distances required are 3 m from inspected pedigreed soybean of the same variety, and 10 m from different soybean varieties, non-pedigreed soybean, and inspected pedigreed soybean of the same variety contaminated with off-types or other varieties.
4.5 Cultivated soybean as a volunteer weed
Soybean seed rarely displays seed dormancy, and only under certain environmental conditions grows as a volunteer in the years following cultivationFootnote 10. Volunteer soybean occurs more in areas with mild winters, for example southwestern Ontario. In areas with cold winters, frost often kills volunteer soybeanFootnote 30. Volunteer soybean may cause yield loss in subsequent crops, harbor plant pathogens between growing seasons, and increase inoculum of soil-borne pathogensFootnote 72. A study in North Dakota found corn yield losses due to season-long volunteer soybean competition were about 56% at high volunteer densities and 3% at low volunteer densitiesFootnote 73. However, volunteer soybean is rarely seen as an economically significant weed and is typically controlled by herbicides and management practices used to control other weeds. Soybean is not listed as a noxious weed in the Weed Seed Order, 2016 and is not listed as a noxious weed in the United StatesFootnote 4.
Because of the low national occurrence and impact of volunteer soybean, research and the control practices discussed in this section are somewhat limited.
4.5.1 Cultural/mechanical control
Soybean volunteers can be reduced by minimizing seed loss during harvest. Seed loss may increase due to
- combining delays after crop maturity
- missed plants
- missed pods due to high cutting height
- equipment inefficiencies (for example, plugged screens, dull cutter bar)
- harvesting when moisture is below 12%Footnote 15, Footnote 73
A ground speed of 4 to 5 km/h and appropriate reel speed also reduces seed lossFootnote 15.
The use of
- planting into weed-free seedbeds
- scouting for weeds
- crop rotation
- cover crops
may further reduce weed pressure, including soybean volunteersFootnote 66, Footnote 74.
4.5.2 Chemical control
Broadleaf herbicides are registered in Canada for volunteer soybean control in wheat (spring, durum, and winter), spring barley, timothy, perennial ryegrass, brome grasses, red fescues, and triticale (spring and winter)Footnote 75. The active ingredients contained in the 2 registered products are from
- Group 4 (Fluroxypyr)
- Group 6 (Bromoxynil)
- Group 27 (Pyrasulfotole)
Studies have evaluated herbicides to control soybean volunteers in sunflowerFootnote 76 and white beanFootnote 31.
The commercialization of herbicide-tolerant soybean has led some growers to experience problems with herbicide-tolerant soybean volunteers in other crops that may require new control methods and recommendationsFootnote 73, Footnote 77. Soybean containing novel herbicide tolerance traits authorized in Canada at the time of writing include soybean with tolerance to
- glufosinate-ammonium (Group 10)
- 2,4-D and dicamba (Group 4)
- glyphosate (Group 9)
- ALS-inhibiting herbicides (Group 2)
- HPPD-inhibitors (Group 27)Footnote 60
Alms et al.Footnote 73, Currie and GeierFootnote 77, and Zollinger and RiesFootnote 78 report the efficacy of several herbicides for herbicide tolerant volunteer soybean control in corn.
The novel herbicide tolerance traits expressed by the volunteer soybean plants and the potential for yield loss are considerations in deciding if and when control is warrantedFootnote 73. Herbicide-tolerant soybean can be controlled using herbicides with other modes of action or by mechanical means.
4.5.3 Integrated weed management
Integrated weed management (IWM) utilizes a combination of biological, cultural, mechanical, and chemical weed control tactics to manage weed populations and increase economic returns. IWM strategies for soybean can include
- the rotation of crops
- use of cover crops
- rotation of herbicide groups
- planting into weed-free seedbeds
- scouting for weeds
- appropriate use of pre-plant/pre-emergence/post-emergence herbicides
- tillageFootnote 66, Footnote 74
4.5.4 Biological control
No biological control methods for soybean volunteers exist.
4.6 Means of movement and dispersal
Soybean is domesticated and only occurs incidentally outside cultivationFootnote 5. Soybean seed is primarily dispersed mechanically by pod dehiscence and seed shattering, a trait that is selected against in breeding programsFootnote 79. Soybean seed can be spread as a result of human activity such as seed transport, harvest, food refuse, or in contaminated commoditiesFootnote 30. The role of animals in soybean dispersal is not well characterized and believed to be minor. While no specific information was found for soybean, birds can play a role dispersing other Glycine speciesFootnote 30. Farm animals, rodents and deer eat soybean seeds, but whether seeds remain viable is unknownFootnote 80, Footnote 81, Footnote 82. Soybeans seeds are not adapted for wind dispersal, and no evidence of this occurring was found. No evidence of water dispersal was found; however, G. soja seeds are rarely dispersed up to 400 m away, possibly by water, as the plants often grow on riverbanksFootnote 83.
5. Related species of soybean
5.1 Inter-species/genus hybridization
The cultivated soybean and its wild progenitor, G. soja, have a center of origin in eastern Asia, and are the only 2 species in the annual subgenus SojaFootnote 84. G. soja is a wild vine-like annual with small and narrow trifoliate leaves, purple flowers and small round brown-black seeds. It grows wild in fields, hedgerows, roadsides and riverbanks in China, Japan, Korea and the Far East area of RussiaFootnote 11. Cytological, morphological and molecular evidence suggest that G. soja is the ancestor of soybeanFootnote 6, Footnote 85.
Soybean can cross with G. soja under field conditions. In Canada, G. soja is occasionally grown in research plotsFootnote 86, Footnote 87, but is not naturalized in North America and there are no reports of its escape to unmanaged habitats. When soybean and G. soja are grown adjacently, some gene flow occurs (<0.1%); this is reduced to almost zero when plants are at least 2 m apartFootnote 88.
In addition to the subgenus Soja, the genus Glycine contains the subgenus Glycine. The Glycine subgenus contains over 26 wild perennial speciesFootnote 1, Footnote 84, including:
- G. clandestina Wendl.
- G. falcate Benth
- G. latifolia Benth.
- G. latrobeana Meissn. Benth
- G. canescens F.J. Herm.
- G. tabacina Labill. Benth.
- G. tomentella Hayata
These species are indigenous to Australia, South Pacific Islands, China, Papua New Guinea, Philippines and TaiwanFootnote 84.
Efforts to cross soybean with wild perennial relatives in the subgenus Glycine have not resulted in fertile offspring under natural conditions. Even using laboratory techniques, creating hybrids between soybean and species in the subgenus Glycine is extremely difficult, hampering efforts to incorporate traits from relatives into soybean breeding programsFootnote 89, Footnote 90, Footnote 91, Footnote 92. Breeders have noted poor crossing ability, early pod abortion and the need for seed rescue techniques to obtain F1 hybridsFootnote 89, Footnote 93. Using in vitro methods, crosses between soybean and G. tomentella resulted in offspring that were successfully backcrossed to soybeanFootnote 51, Footnote 93, Footnote 94. Some in vitro crosses between soybean and G. clandestina resulted in sterile hybrid offspringFootnote 89. Sterile hybrids were produced crossing soybean and G. canescens using transplanted endosperm as a nurse layerFootnote 95.
5.2 Potential for introgression of genetic information from soybean into relatives
Relatives of soybean do not naturally occur in Canada. The likelihood of gene flow from soybean to G. soja outside of breeding programs is very remote in Canada. In the absence of sexually compatible species related to soybean in Canada, the potential for interspecific gene flow is negligible.
6. Potential interaction of soybean with other life forms
The interactions of soybean with other life forms in Canada are well characterized, and information is readily available on the management of many diseases and insect pests of soybean.
Numerous pathogenic species can decrease soybean yield and crop quality. The most common diseases of soybean in Canada include
- seed rots and seedling blights (Pythium, Fusarium and Rhizoctonia species)
- phytophthora root rot (Phytophthora sojae)
- rhizoctonia root rot (Rhizoctonia solani)
- phomopsis seed decay (Phomopsis longicolla)
- pod and stem blight (Diaporthe phaseolorum var. sojae)
- soybean sudden death syndrome (Fusarium virguliforme)
- white mould (Sclerotinia sclerotiorum)Footnote 74
Major insect pests of soybean include
- the seedcorn maggot (Delia platura)
- the soybean aphid (Aphis glycines)
- the bean leaf beetle (Cerotoma trifurcata)Footnote 74
Other insect pests include
- defoliators (Lepidoptera, Coleoptera, Orthoptera)
- phloem feeders (Hemiptera)
- seed and pod feeders (Coleoptera, Diptera)
- stem borers
- root feeders (Coleoptera, Diptera, Lepidoptera)Footnote 11
Globally, about 24 genera and many species of plant-parasitic nematodes are associated with soybeanFootnote 11. Soybean cyst nematode (Heterodera glycines) causes the greatest economic loss in soybeanFootnote 42. Other pests include the sedentary nematodes of Meloidogyne species (root-knot nematodes) and the migratory endoparasites of Pratylenchus species (root-lesion nematodes)Footnote 96.
Soybean forms a symbiosis with a range of Rhizobium species, which invade the root hair and form a nodule from which they provide the plant with nitrogenFootnote 97. B. japonicum is added to soybean fields in a process called inoculation. Once present, rhizobia will survive in most soils for 7 to 10 yearsFootnote 15.
Please refer to the tables below for examples of interactions of Glycine max with other life forms during its life cycle:
- Table 1: Fungi
- Table 2: Bacteria
- Table 3: Viruses
- Table 4: Insects
- Table 5: Nematodes
- Table 6: Animals
- Table 7: Plants
Abbreviation list for tables
- BC – British Columbia
- AB – Alberta
- SK – Saskatchewan
- MB – Manitoba
- ON – Ontario
- QC – Quebec
- NB – New Brunswick
- NS – Nova Scotia
- PE - Prince Edward Island
- NL – Newfoundland & Labrador
|Fungi||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
(Kirchner 1896) Jordan (Soybean rhizobia)
|Symbiont||Widespread||(OMAFRA, 2017Footnote 15)|
(T. Matsumoto & Tomoy.)
(Cercospora leaf blight and purple seed stain diseases)
|Pathogen||QC, ON, MB||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; CABI, 2017Footnote 99)|
K. Hara (Frogeye leaf spot)
|Pathogen||ON||(OMAFRA, 2017Footnote 15; Ginns 1986Footnote 100)|
(Schwein.) Andrus & W.D. Moore (Anthracnose)
|Pathogen||ON, MB, SK||(AAFC, 2013Footnote 98; Buchwaldt et al., 2004Footnote 101)|
|Diaporthe phaseolorum var. caulivora
Athow & Caldwell (Stem canker)
|Pathogen||ON, QC||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; Hall & Xue, 1995Footnote 102)|
|Diaporthe phaseolorum var. sojae
(Lehman) Wehm. (Pod and stem blight)
|Pathogen||ON||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98)|
(Fusarium wilt, blight, seed and root rot)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; Hartman et al., 2015Footnote 103)|
O'Donnell & T. Aoki (Soybean sudden death syndrome)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98)|
Cooke & Peck (Powdery mildew)
|Pathogen||ON||(OMAFRA, 2017Footnote 15; CABI, 2017Footnote 99)|
|Mychorrhizal fungi||Symbiont||Widespread||(Bethlenfalvay et al., 1982Footnote 104)|
|Peronospora trifoliorum var. manshurica
Naumov (Downy mildew)
|Pathogen||NS, QC, ON, MB, BC||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; CABI, 2017Footnote 99)|
|Phakospora pachyrhizi Syd. & P. Syd.
(Asian Soybean rust)
|Pathogen||ON||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98)|
(Allington & D.W. Chamb.) W. Gams (Brown stem rot)
|Pathogen||ON||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98)|
T. W. Hobbs (Phomopsis seed decay)
|Pathogen||ON, MB||(OMAFRA, 2017Footnote 15; Pradhan et al., 2019Footnote 105)|
Kaufmann and Gerdemann (root and stalk rot)
QC, ON, MB
|(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; Pradhan et al., 2019Footnote 105)|
(Pythium root rot)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98)|
J.G. Kühn (Rhizoctonia stem and root rot)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; Pradhan et al., 2019Footnote 105)|
(Lib.) de Bary
(Sclerotinia stem rot / White mould)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; Hartman et al., 2015Footnote 103)|
Hemmi (Brown spot)
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; Pradhan et al., 2019Footnote 105)|
|Bacteria||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Pseudomonas syringae Van Hall
|Pathogen||Widespread||(OMAFRA, 2017Footnote 15; AAFC, 2013Footnote 98; CABI, 2017Footnote 99)|
|Xanthomonas axonopodis pv glycines (Xag) (Bacterial pustule)||Pathogen||QC, ON, MB||(AAFC, 2013Footnote 98; Hartman et al., 2015Footnote 103)|
|Viruses||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Alfalfa mosaic virus (AMV)||Pathogen||Widespread||(Hartman et al., 2015Footnote 103)|
|Bean pod mottle virus (BPMV)||Pathogen||Widespread||(OMAFRA, 2017Footnote 15; Hartman et al., 2015Footnote 103)|
|Soybean mosaic virus (SMV)||Pathogen||Widespread||(OMAFRA, 2017Footnote 15; Hartman et al., 2015Footnote 103)|
|Tobacco ringspot virus (TRSV)||Pathogen||Widespread||(Hartman et al., 2015Footnote 103)|
|Insects||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Anticarsia gemmatalis (Hübner) (Velvetbean caterpillar)||Consumer||QC, ON||(Herzog & Todd, 1980Footnote 106)|
|Aphis glycines Matsumura (Soybean aphid)||Consumer||QC, ON, MB||(OMAFRA, 2017Footnote 15; CABI, 2017Footnote 99; Manitoba Agriculture, 2006Footnote 107; Hallett et al., 2014Footnote 108)|
|Cerotoma trifurcata Forster (Bean leaf beetle)||Consumer||QC, ON, MB||(OMAFRA, 2017Footnote 15; Bousquet et al., 2013Footnote 109)|
|Cutworms (various species)||Consumer||Widespread||(OMAFRA, 2017Footnote 15; Arnett Jr, 2010Footnote 110)|
|Delia platura (Meigen) (Seedcorn maggot)||Consumer||Widespread||(Miller & McClanahan, 1960Footnote 111)|
|Epilachna varivestis Mulsant (Mexican bean beetle)||Consumer||NB, QC, ON||(OMAFRA, 2017Footnote 15; Bousquet et al., 2013Footnote 109; Kogan, 1972Footnote 112)|
|Euschistus servus (Say) (Brown stink bug)||Consumer||Widespread||(OMAFRA, 2017Footnote 15; McPherson & McPherson, 2000Footnote 113)|
|Family Acrididae, grasshoppers spp.||Consumer||Widespread||(Seagraves & Lundgren, 2012Footnote 114; Vickery & Kevan, 1985Footnote 115)|
|Family Aleyrodidae, whiteflies||Consumer||Widespread||(Maw et al., 2000Footnote 116; McPherson & Lambert, 1995Footnote 117; Rice, 2007Footnote 118)|
|Family Chrysopidae, green lacewings||Beneficial organism||Widespread||(Samaranayake & Costamagna, 2018Footnote 119)|
|Family Coccinellidae, lady beetles||Beneficial organism||Widespread||(Hallett et al., 2014Footnote 108; Samaranayake & Costamagna, 2018Footnote 119)|
|Family Hemerobiidae, brown lacewings||Beneficial organism||Widespread||(Samaranayake & Costamagna, 2018Footnote 119)|
|Family Nabidae, damsel bugs||Beneficial organism||Widespread||(Samaranayake & Costamagna, 2018Footnote 119)|
|Halyomorpha halys Stål (Brown marmorated stink bug)||Consumer||QC, ON, BC||(Abram et al., 2018Footnote 120)|
|Helicoverpa zea (Boddie) (Corn earworm)||Consumer||Widespread||(OMAFRA, 2017Footnote 15; Walker et al., 2000Footnote 121)|
|Hypena scabra (Fabricius) (Green cloverworm)||Consumer||Widespread||(Maw, 2000Footnote 116; Young, 1986Footnote 122)|
|Lygus lineolaris (Palisot de Beauvois) (Tarnished plant bug)||Consumer||Widespread||(Maw et al., 2000Footnote 116; Young, 1986Footnote 122)|
|Orius insidiosus (Say) (Insidious flower bug)||Beneficial organism||Widespread||(Hallett et al., 2014Footnote 108)|
|Phyllophaga spp. (June beetle)||Consumer||Widespread||(Bousquet et al., 2013Footnote 109; Lentz, 1985Footnote 123)|
|Podisus maculiventris (Say) (Spined soldier bug)||Beneficial organism||Widespread||(O'Neil, 1988Footnote 124)|
|Popillia japonica Newman (Japanese beetle)||Consumer||NS, PE, NB, QC, ON||(Bousquet et al., 2013Footnote 109; Yesudas et al., 2010Footnote 125)|
|Pseudoplusia includens Walker (Soybean looper)||Consumer||NS, QC, ON||(CABI, 2017Footnote 99)|
|Wireworms (Limonius spp., Melanotus spp., and others)||Consumer||Widespread||(Bousquet et al., 2013Footnote 109; Keaster et al., 1975Footnote 126)|
|Nematodes||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Heterodera glycines Ichinohe (Soybean cyst nematode)||Consumer||QC, ON, MB||(OMAFRA, 2017Footnote 15)|
|Meloidogyne spp. (Root knot nematode)||Consumer||Widespread||(AAFC, 2013Footnote 98)|
|Animals||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Animal browsers (for example, deer, groundhog, mice)||Consumer||Widespread||(Kaufman & Kaufman, 2017Footnote 81; MacGowan et al., 2006Footnote 82; Nelson et al., 1988Footnote 80)|
|Birds (for example, blackbirds, flycatchers, sparrows)||Consumer, Beneficial organism||Widespread||(Kirk et al., 2001Footnote 127)|
|Earthworms||Beneficial organism||Widespread||(Eriksen-Hamel & Whalen, 2007Footnote 128)|
|Millipedes||Beneficial; Consumer||Widespread||(OMAFRA, 2017Footnote 15)|
|Slug (Deroceras reticulatum)||Consumer||Widespread||(Barratt et al., 1994Footnote 129; Hahn et al., 2011Footnote 130)|
|Tetranychus urticae Koch (Two-spotted spider mite)||Consumer||NS, QC, ON, BC||(OMAFRA, 2017Footnote 15; CABI, 2017Footnote 99)|
|Plants||Interaction with Glycine max (pathogen; symbiont or beneficial organism; consumer; gene transfer)||Presence in Canada||Reference(s)|
|Glycine soja Siebold & Zucc.||Gene transfer||Absent||(OECD, 2000Footnote 10)|
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