The biology of Sinapis alba L. (mustard)

Biology document BIO2022-01: A companion document to Directive 94-08 (Dir94-08), Assessment Criteria for Determining Environmental Safety of Plant with Novel Traits.

On this page

1. 1. General administrative information
   1. 1.1 Background
   2. 1.2 Scope
2. 2. Identity
   1. 2.1 Name(s)
   2. 2.2 Family
   3. 2.3 Synonym(s)
   4. 2.4 Common name(s)
   5. 2.5 Taxonomy and genetics
   6. 2.6 General description
3. 3. Geographical distribution
   1. 3.1 Origin and history of introduction
   2. 3.2 Native range
   3. 3.3 Introduced range
   4. 3.4 Potential range in North America
   5. 3.5 Habitat
4. 4. Biology
   1. 4.1 Reproductive biology
   2. 4.2 Breeding and seed production
   3. 4.3 Cultivation and use as a crop
   4. 4.4 Gene flow during commercial seed and biomass production
   5. 4.5 Cultivated S. alba as a volunteer weed
      1. 4.5.1 Cultural/mechanical control
      2. 4.5.2 Chemical control
      3. 4.5.3 Integrated weed management
   6. 4.6 Means of movement and dispersal
5. 5. Related species of S. alba
   1. 5.1 Inter-species/genus hybridization
   2. 5.2 Potential for introgression of genetic information from S. alba into relatives
6. 6. Potential interaction of S. alba with other life forms
7. 7. References

1. General administrative information

1.1 Background

The Canadian Food Inspection Agency's (CFIA) Plant 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 Dir94-08: Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits.

1.2 Scope

This document is intended to provide background information on the biology of S. alba, including:

• its identity
• geographical distribution
• reproductive biology
• related species
• the potential for gene introgression from S. alba 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:

• weediness/invasiveness
• gene flow
• plant pest properties
• impacts on other organisms
• impacts on biodiversity

2. Identity

2.1 Name(s)

Sinapis alba L.^Footnote 1

2.2 Family

Brassicaceae (alt. Cruciferae) family, commonly known as the mustard family^Footnote 1.

2.3 Synonym(s)

The most encountered synonym for S. alba is Brassica hirta Moench. The name B. hirta was given by Moench in 1802; in 1839, Rabenhorst named this species Brassica alba (L.) Rabenh.; ultimately, the name Sinapis alba L. was adopted^Footnote 2.

Other synonyms for S. alba include:

• Bonannia officinalis C.Presl
• Brassica alba Moench
• Brassica foliosa (Willd.) Samp.
• Crucifera lampsana E.H.L.Krause
• Eruca alba (L.) Noulet
• Leucosinapis alba (L.) Spach
• Napus leucosinapsis K.F.Schimp. & Spenn.
• Raphanus albus (L.) Crantz
• Rhamphospermum album (L.) Andrz. ex Rchb.
• Rorippa coloradensis Stuckey
• Sinapis alba ssp. dissecta (Lag.) Bonnier
• Sinapis alba var. melanosperma Alef.
• Sinapis foliosa Willd.^Footnote 3,^Footnote 4,^Footnote 5

2.4 Common name(s)

The common name 'mustard' can refer to multiple species, including S. alba and Brassica juncea (L). Czern & Coss. (brown and oriental mustard)^Footnote 6,^Footnote 7. S. alba is commonly known as white mustard and yellow mustard^Footnote 1,^Footnote 5,^Footnote 8. It may also be referred to as:

• charlock
• kedlock
• rough mustard
• tame mustard^Footnote 3

2.5 Taxonomy and genetics

S. alba has 2n = 24 chromosomes^Footnote 9,^Footnote 10.

There are 3 subspecies of S. alba; only S. alba subsp. alba is naturalized in North America:

• Sinapis alba subsp. alba (cultivated)
• Sinapis alba subsp. dissecta (Lag.) Simonk.
• Sinapis alba subsp. mairei (H.Lindb.) Maire^Footnote 1,^Footnote 11

2.6 General description

Plants grow to approximately 1 m^Footnote 12,^Footnote 13. S. alba has yellow, alternate flowers with 4 sepals alternating with 4 petals, typical of the Brassicaceae^Footnote 3. Leaves are deeply pinnately lobed^Footnote 14. Pods are 2.0 to 4.2 centimetres long and have a long flat beak that occupies about one-third of the length^Footnote 8. Pods contain 2 to 4 seeds in each loculus separated by a false septum^Footnote 8. Both yellow- and brown-seeded forms exist, with yellow-seeded S. alba commonly cultivated^Footnote 7,^Footnote 8. Seeds are spherical or oval, approximately 2 to 3 millimetres in diameter^Footnote 15.

S. alba has a similar life cycle and growth pattern to Brassica napus L. (canola/rapeseed). The phenological growth stages of S. alba can be classified using the BBCH system^Footnote 16.

Principal growth stages

• 0: germination
• 1: leaf development
• 2: side shoot development
• 3: stem elongation
• 4: vegetable plant part development
• 5: inflorescence emergence
• 6: flowering
• 7: fruit development
• 8: ripening
• 9: senescence

These main growth stages can be further subdivided to indicate points in plant development^Footnote 7.

S. alba may be confused with Sinapis arvensis L. (wild mustard) and other annual yellow-flowered mustards. A key to identifying mature plants including S. alba and S. arvensis can be found in Warwick, Beckie^Footnote 17.

3. Geographical distribution

3.1 Origin and history of introduction

S. alba originates from the Middle East and Mediterranean regions^Footnote 18,^Footnote 19. S. alba has been cultivated as a condiment crop for thousands of years^Footnote 18. In the western Canadian prairies, commercial production of S. alba began on a small scale in 1936^Footnote 12. The Canadian mustard acreage (combined production of S. alba and Brassica juncea) gradually increased. In 1951, 40,850 acres were seeded in Canada. Acreage climbed to 131,050 acres in 1960 and 200,000 acres in 1970. Since 1970, the annual seeded acres have ranged from 87,000 (1976) to 840,000 (2003)^Footnote 20. S. alba usually makes up 40 to 60 percent of the mustard acreage^Footnote 21.

3.2 Native range

The native range of S. alba includes the Mediterranean Region and some surrounding countries^Footnote 1. The Mediterranean Region includes parts of Europe, Africa, and Asia.

3.3 Introduced range

S. alba is introduced and widely naturalized in:

• Canada
• the continental United States
• the Caribbean Territories^Footnote 1,^Footnote 5

3.4 Potential range in North America

S. alba occurs over a large range in Canada, including in the YK, BC, AB, SK, MB, ON, QB, NB, NS, and PE^Footnote 22,^Footnote 23,^Footnote 24. S. alba is predominantly found in areas it is cultivated, primarily in the brown and dark brown soil zones of the western Canadian Prairies and the northern Great Plains of the United States^Footnote 8. S. alba is uncommon in the Maritime provinces^Footnote 22,^Footnote 23. The potential future range includes all Canadian provinces and territories.

Geographical abbreviations:

• YK: Yukon
• NT: North West Territories
• NU: Nunavut
• BC: British Columbia
• AB: Alberta
• SK: Saskatchewan
• MB: Manitoba
• ON: Ontario
• QB: Quebec
• NB: New Brunswick
• NS: Nova Scotia
• PE: Prince Edward Island
• NF: Newfoundland
• LB: Labrador

3.5 Habitat

S. alba is a cool-season crop that can perform well in a short growing season^Footnote 7. S. alba can occur in cultivated fields, disturbed prairies, roadsides, and disturbed areas^Footnote 3,^Footnote 24. S. alba is primarily found in agricultural environments, where it can grow as a volunteer in the years following cultivation^Footnote 25.

4. Biology

4.1 Reproductive biology

Flowering

S. alba is a long-day plant^Footnote 26. Typically, long-day plants require light periods longer than a certain critical length to flower. However, Bodson et al. (1977) found it was possible to induce some flowering over 3 short days under experimental conditions^Footnote 26.

Pollen dispersal

At the time of writing, there is limited information on pollen dispersal distances and characteristics in S. alba. In a field experiment with plots of 4 rows of 10 meters and 45 cm between the rows, the intercrossing between neighbouring plots exceeded 30 percent^Footnote 27. S. alba must be at least 200 meters from other varieties of S. alba and non-pedigreed S. alba to obtain adequate purity in Foundation or Registered seed^Footnote 28. The pollen yield in S. alba is variable, typically ranging from 7 to 12 mg/10 flowers^Footnote 29. S. alba pollen can be dispersed by insects and wind^Footnote 18,^Footnote 29. Because of its nectar and pollen production, S. alba is recommended as a good melliferous plant^Footnote 29. S. alba flowers are adapted to pollination by short-tongued bees and flies^Footnote 29,^Footnote 30. Naumkin and Velkova (2013) identified and quantified insect pollinators in Russian S. alba fields from 2000 to 2012^Footnote 31. Pollinators included:

• wild bees (Apidae)
• anthomyias (Anthomyiidae)
• honey bees (Apis mellifera)
• flower flies (Syrphidae)
• golden-eyed flies (Chrysophidae)
• lady beetles (Coccinellidae)
• bumblebees (Bombus spp.)^Footnote 31

Pollination

S. alba is an obligate outcrossing species^Footnote 32. Olsson (1960) measured the degree of outcrossing between individual plants of S. alba in experimental field plots to be up to 99.6%^Footnote 27. The self-incompatibility mechanism is discussed in Śnieżko and Winiarczyk (1996)^Footnote 32. When flowers are pollinated with pollen from the same plant, pollen grains can germinate on the stigma, but they do not grow in the pistil tissue.

Maturity

S. alba reaches maturity after approximately 3 months^Footnote 12,^Footnote 13.

4.2 Breeding and seed production

Standard breeding techniques

As S. alba is an obligate outcrossing species^Footnote 27, recurrent selection has been widely used in breeding programs^Footnote 33. Recurrent selection is not always effective for seed yield increase due to low heritability and limited natural variation within S. alba^Footnote 10,^Footnote 12. 3 varieties of S. alba (AC Pennant, AC Base and Andante) were developed from the same base population through several cycles of recurrent selection^Footnote 13. Rakow et al. (2009) explains the pedigree and selection scheme for these cultivars^Footnote 13.

Microspore production for S. alba has not been successful^Footnote 34. Seed mutagenesis can be used^Footnote 34.

Traits targeted by breeding programs

S. alba has uniformly high levels of hydroxybenzyl glucosinolate and resistance to many insects and diseases^Footnote 12. Most breeding efforts have focused on:

• seed-yield increase^Footnote 8,^Footnote 12,^Footnote 13
• lower husk-to-embryo ratio^Footnote 12
• lower green seed count^Footnote 12
• development of an edible oilseed S. alba for the production of vegetable oil and high protein meal^Footnote 35,^Footnote 36
• increased seed mucilage content^Footnote 13
• bright yellow seed colour^Footnote 13
• herbicide tolerance^Footnote 34

Seed production

Historically, the highest-quality commercial seed from the previous year's production was selected and grown in subsequent years. These landraces are believed to have been brought over from Europe, though the exact origins are unknown^Footnote 12. Currently, S. alba is subject to variety registration listed on Schedule 3 of the Seeds Regulations (C.R.C., c. 1400). The Canadian Seed Growers Association has developed varietal purity standards for pedigree seed production of foundation, registered and certified seed^Footnote 28. The Prairie Recommending Committee for Oilseeds evaluates the merit of new varieties and recommends varieties to the CFIA's Variety Registration Office^Footnote 21.

4.3 Cultivation and use as a crop

Cultivation

Common practices applied during the cultivation of S. alba (for example, seeding, fertilization, chemical treatments, rotation, and harvesting) are discussed in detail in provincial crop production guides and extension material. Please refer to:

• the Saskatchewan Mustard Development Commission's Mustard Production Manual^Footnote 7
• the Government of Alberta's publication 'Mustard Production for Alberta'^Footnote 15
• the Government of Manitoba's Guide to Mustard – Production and Management^Footnote 37

Crop rotation

Often, S. alba follows a cereal crop in rotation. A break of several years between canola and mustards is often implemented to prevent contamination of mustard grain with canola containing genetically-engineered traits. In the brown and dark brown soil zones where S. alba is primarily grown, moisture is often limiting and rotating between deep and shallow-rooted crops can help manage soil moisture^Footnote 7.

Weeds

Problematic weeds include:

• annual sow thistle (Sonchus asper)
• ball mustard (Neslia paniculata)
• Canada thistle (Cirsium arvense)
• cleavers (Galium aparine)
• common groundsel (Senecio vulgaris)
• cow cockle (Saponaria vaccaria)
• dandelion (Taraxacum officinale)
• dog mustard (Erucastrum gallicum)
• field bindweed (Convolvulus arvensis)
• kochia (Bassia scoparia)
• narrow leaved hawk's beard (Crepis tectorum)
• perennial sow thistle (Sonchus arvensis)
• shepherd's purse (Capsella bursa-pastoris)
• stinkweed (Thlaspi arvense)
• stork's bill (Erodium cicutarium)
• tartary buckwheat (Fagopyrum tataricum)
• volunteer canola
• wild buckwheat (Polvgonum convolvulus)
• wild mustard
• wild oat (Avena fatua)^Footnote 7,^Footnote 15,^Footnote 37

There are limited in-crop herbicides for use on S. alba. Many of these weeds have no registered in-crop herbicides to control them^Footnote 15. Control of herbicide resistant weed biotypes in S. alba is challenging. Therefore, integrated weed management is important for controlling weeds in S. alba. Best practices include increasing the competitiveness of S. alba:

• using higher seeding rates
• seeding shallow
• using narrow row spacing
• providing optimal fertility
• using clean seed
• seeding early
• avoiding planting into fields with high weed pressure^Footnote 7

Health Canada's Pest Management Regulatory Authority maintains a database of approved herbicides^Footnote 38. Please refer to this database for current information on registered herbicides for weed control in S. alba. Some herbicides may only be registered for use and sale in some provinces. Some herbicides may also be registered using a minor use registration.

The following herbicides may be applied to the soil before seeding, either in the late fall or in the early spring. Active ingredients include:

• triallate – a Group 8 (lipid synthesis inhibitors) herbicide used to control wild oat
• trifluralin – a Group 3 (microtubule assembly inhibitors) herbicide used to control a variety of broadleaf and grassy weeds
• sulfentrazone – a Group 14 (protoporphyrinogen oxidase inhibitors) herbicide used to control kochia
• ethalfluralin – a Group 3 herbicide used to control many broadleaf and grassy weeds^Footnote 7

Some Group 1 (ACCase inhibitors) herbicides, for example, clethodim, quizalofop, and sethoxydim, can be used for post-emergent control of grassy weeds^Footnote 7,^Footnote 38,^Footnote 39. Glyphosate (Group 9: inhibitors of EPSP synthesis) can be used pre-harvest to control perennial weeds the following season^Footnote 7. Saflufenacil (Group 14) can be used as a desiccant^Footnote 38.

Use

The major market for S. alba is the North American condiment industry, where uses include traditional hot dog mustard, mayonnaise, and salad dressings^Footnote 7. S. alba may also be used:

• as a water-binding agent and protein extender in prepared meats^Footnote 7
• as a feedstock for biodiesel production^Footnote 40
• for varied industrial applications because the seed coat mucilage has emulsifying, water-holding, and stabilizing properties^Footnote 41
• as a forage^Footnote 42

S. alba seed powder has been considered for use a bioherbicide^Footnote 43,^Footnote 44.

4.4 Gene flow during commercial seed and biomass production

S. alba is not invasive of natural habitats in Canada. Therefore, the potential risk of gene flow to wild populations of S. alba is negligible.

Gene flow to cultivated populations of S. alba grown in proximity may occur. The Canadian Seed Growers' Association (CSGA) has set standards for producing foundation, registered and certified S. alba seed^Footnote 28.

4.5 Cultivated S. alba as a volunteer weed

Following cultivation, volunteer S. alba can become weedy in subsequent crops. S. alba may also occur in prairies, roadsides, and disturbed areas^Footnote 3,^Footnote 11,^Footnote 25,^Footnote 45,^Footnote 46. We found no record of substantial populations of S. alba in natural environments in Canada. S. alba is not listed in the Weed Seeds Order, 2016.

S. alba has not become an abundant weed despite cultivation since the 1930s in western Canada. It does not exhibit the weedy characteristics of S. arvensis. The difference in weed ranking among cultivated Brassicaceae species is largely attributed to differences in the acreage and, more recently, herbicide resistance in some species. S. alba may be less likely than some other Brassicaceae species to become a problematic volunteer weed because of attributes including shatter resistance. Weedy forms of S. alba occur in the Mediterranean region and some countries where S. alba is used as a green manure crop^Footnote 47. In its native range, S. alba has developed tolerance to some Group 2 herbicides^Footnote 24,^Footnote 48. Changes to the acreage or agronomic characteristics of S. alba in Canada may cause it to become more prevalent as a weed.

Seed dormancy

No studies were found that evaluated the length of time S. alba could remain in the seedbank in the Canadian environment. Cultivated S. alba does not exhibit notable levels of seed dormancy; seeds are often referred to as 'non-dormant'^Footnote 49. Under suitable conditions, including adequate moisture and temperatures of at least 5 degrees celsius, seeds will germinate within 4 to 5 days^Footnote 49. Seeds can germinate within 24 hours when temperatures are approximately 20 degrees celsius^Footnote 49.

A study of seed dormancy in wild S. alba seeds collected in Israel found that dormancy was higher in seeds collected in the dry, hot southern part of Israel than seeds collected from the cooler, wetter northern region^Footnote 50. Temperature also played a role, with some seeds only expressing dormancy at high temperatures^Footnote 50. Germination of previously dormant S. alba seeds has been observed in the presence of gibberellic acid^Footnote 50. Seed dormancy is observed in the related weedy species S. arvensis^Footnote 51.

Susceptibility to shattering

S. alba pods rarely shatter at maturity^Footnote 8,^Footnote 52. Some intact ripe pods may be left in the field following harvest due to wind or mechanical action^Footnote 47.

Seed size

Seeds are large (approximately 4 to 6.1 grams per 1000 seeds) relative to canola (Brassica napus and B. rapa: 2 to 3 grams per 1000 seeds)^Footnote 8,^Footnote 13.

4.5.1 Cultural/mechanical control

Reducing harvest losses will minimize the number of potential S. alba volunteers. Losses can be reduced by properly setting combines and sealing any leaks. Control of S. alba volunteers in other crops or in fallow ground can readily be achieved by mechanical means.

4.5.2 Chemical control

Volunteer S. alba can be controlled using herbicides including:

• Bromoxynil/MCPA
• Dicamba + MCPA
• Dicamba/mecoprop/MCPA
• Fluroxypyr + MCPA
• Imazamox
• Imazamox/Imazethapyr
• Clopyralid/MCPA + Fluroxypyr^Footnote 39

4.5.3 Integrated weed management

S. alba volunteers rarely require special consideration in a weed management program. 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 S. alba volunteers can include:

• scouting for weeds
• seeding at an optimum rate with high-quality seed to maximize competition and suppression of weeds
• planting into weed-free seedbeds
• appropriate use of herbicides
• reducing harvest loss
• tillage^Footnote 15

4.6 Means of movement and dispersal

S. alba seed may disperse through pod shatter, seed spillage during human use (for example, during transportation), and as a contaminate of other crop seeds. Dry conditions between physiological maturity and straight combining and wind movement within the crop canopy can result in more pods breaking off or splitting open and losing seeds^Footnote 53. Under adverse harvesting conditions in a Saskatchewan study, 5.2 percent of S. alba seeds were lost, compared to 1.4 percent under low shattering conditions^Footnote 53. Other mechanisms for the movement and dispersal of S. alba seeds are unclear. S. alba seeds might be dispersed by organisms that consume the seeds. Their ability to become established may depend upon the receiving environment; no reports of significant feral populations in natural environments were found.

5. Related species of S. alba

As stated in Section 2.5 Taxonomy and genetics, S. alba is a member of the tribe Brassiceae of the Brassicaceae family. Within the tribe Brassiceae, species can be divided into 2 evolutionary lineages: the Rapa/Oleracea lineage and the Nigra lineage^Footnote 54. S. alba appears to be most closely related to the Nigra lineage^Footnote 55. Further research is needed to clarify which species are wild crop relatives with the potential to receive gene flow from S. alba. The species in the Brassicaceae family were originally categorized primarily based on morphological characteristics; more recently, molecular research is providing continued insights into the evolutionary relationships. The genus Sinapis is polyphyletic: it includes 3 clades which each show a closer relationship to Brassica species or other members of the tribe Brassiceae than to each other^Footnote 55,^Footnote 56,^Footnote 57,^Footnote 58,^Footnote 59. S. alba appears to be more closely related to Kremeriella cordylocarpus (2n = 24), Hemicrambe fruticulosa (2n = 18), Coincya (5 spp. 2n = 24) and, possibly some species in Diplotaxis than to S. arvensis.

The genus Sinapis includes 6 species:

• Sinapis alba L.
• Sinapis allionii Jacq.
• Sinapis arvensis L.
• Sinapis circinata Desf.
• Sinapis flexuosa Poir.
• Sinapis pubescens L.^Footnote 5

Of these, only S. alba and S. arvensis (charlock mustard, field mustard, wild mustard) are present in Canada.

S. arvensis is widespread in Canada and listed under Class 3 of the Canadian Weed Seeds Order, 2016 under the Seeds Act. S. arvensis is recorded in NT, YK, LB, NF, NS, PE, NB, QC, ON, MB, SK, AB, and BC^Footnote 24. Frankton and Mulligan (1987) list it as a common annual weed; less problematic east of Manitoba^Footnote 25. It is most abundant in Manitoba (Warwick et al., 2000a). In Saskatchewan, S. arvensis is considered a problematic weed, including in lentil production^Footnote 60. Its habitats include grain fields, cultivated fields, waste areas, fence rows, and roadsides. Controlling herbicide tolerant S. arvensis can be an agronomic challenge^Footnote 61. The range of S. arvensis overlaps with the range of S. alba production at it is expected that these 2 species will grow in the same areas.

Brassicaceae comprises approximately 324 genera, including the following agronomically-important species:

• Brassica rapa (oilseed rape, Polish canola, turnip, bird rape)
• Brassica napus (Argentine rape, swede rape)
• Brassica juncea (brown mustard, Indian mustard)
• Brassica carinata (Ethiopian mustard)
• Brassica nigra (black mustard)
• Brassica oleracea (cabbage, cauliflower, Brussel sprouts, broccoli, Chinese cabbage, kale, kohlrabi)
• Raphanus sativus (radish)
• Camelina sativa (camelina)^Footnote 1

The following details the distribution and habitat for each of these species in Canada, according to Warwick et al. (2013)^Footnote 24.

Brassica rapa is recorded in NT, YK, LB, NF, NS, PE, NB, QB, ON, MB, SK, AB, and BC. Frankton and Mulligan (1987) suggest that it is sometimes abundant and that in some parts of the East, the wild form, bird rape, supplants S. arvensis over large areas^Footnote 25. For more information, see The Biology of Brassica rapa L^Footnote 62.

Brassica napus is recorded in NT, LB, NF, PE, NS, NB, QC, ON, MB, SK, AB, and BC. B. napus is not listed in Frankton and Mulligan (1987) but has become increasingly abundant as a volunteer weed^Footnote 25. It ranked 18th in abundance during the 1970s and had risen to 14th since 2000 (Leeson et al., 2005). For more information, see The Biology of Brassica napus L. (Canola/Rapeseed)^Footnote 63.

Brassica juncea is recorded in NT, NF, PE, NS, NB, QC, ON, MB, SK, AB, and BC. Frankton and Mulligan (1987) report that B. juncea occurs in every province and reaches its greatest abundance in the western provinces^Footnote 25. For more information, see The Biology of Brassica juncea (Canola/Mustard)^Footnote 64.

Brassica carinata has been successfully cultivated across Canada. For more information, see The Biology of Brassica carinata (A.) Braun (Abyssinian cabbage)^Footnote 65.

Brassica nigra is recorded in NF, NS, NB, QC, ON, SK, AB, and BC. Frankton and Mulligan (1987) suggest that it is not very common in western Canada^Footnote 25.

Brassica oleracea is recorded in BC, AB, ON, and QC. B. oleracea rarely escapes from cultivation and is mainly found in fields, roadsides, and waste places.

Raphanus sativus is recorded in NU, NF, NS, PE, NB, QC, ON, MB, AB, SK, and BC. Frankton and Mulligan (1987) indicate that this species is occasionally persistent in gardens as a result of cultivation^Footnote 25.

Camelina sativa is recorded in NT, BC, AB, SK, MB, ON, and QC. As a weed, C. sativa can be found in prairies, fields (grain, flax, alfalfa), open woods, lakeshore, around elevators, roadsides, railways, and waste places. For more information, see The Biology of Camelina sativa (L.) Crantz (Camelina)^Footnote 6.

Weed species found in Canada in the Brassicaceae family include:

• Alliaria petiolata (garlic mustard)
• Berteroa incana (hoary alyssum, false hoary madwort)
• Capsella bursa-pastoris (Shepherd's purse)
• Descurainia sophia (flixweed)
• Diplotaxis muralis (sand rocket, stinking wall rocket)
• Erucastrum gallicum (dog mustard)
• Lepidium draba (hoary cress)
• Raphanus raphanistrum (wild radish)
• Sisymbrium spp.
• Thlaspi arvense (stinkweed)

The following details the distribution and habitat for each of these species in Canada, according to Warwick et al. (2003)^Footnote 24 unless otherwise cited.

Alliaria petiolata is recorded in BC, ON, QC, and NB. It is a winter annual or biennial that occurs in mixed to rich deciduous woodlands, fields, streamsides, gardens, roadsides, and waste places.

Berteroa incana is recorded in BC, AB^Footnote 66, SK, MB, ON, QC, NB, and NS. It is a annual or biennial that occurs in dry fields, pastures, parklands, farmyards, edges of woods, gravel and sand pits, waterways, roadsides, and waste places.

Capsella bursa-pastoris is recorded in YK, NT, NU, BC, AB, SK, MB, ON, QC, NB, NS, PE, NF, and LB. It is an annual weed that occurs in cultivated fields (grain, hay, canola, potato, strawberry), gardens, orchards, vineyards, woods, pastures, meadows, flats, beaches, roadsides, railways, and waste places.

Descurainia sophia is recorded in YK, NT, BC, AB, SK, MB, ON, QC, NB, NS, PE, and NF. It is an annual or biennial found in dry disturbed meadows, grasslands, pastures, valleys, prairies, gardens, barnyards, grain and hay fields, roadsides, railways, and waste places.

Diplotaxis muralis is recorded in NS, PE, NB, QC, ON, MB, SK, and AB. Darbyshire (2003) lists it as an occasional weed of shores, railway lines, roadsides and disturbed areas^Footnote 3. D. muralis is particularly abundant in irrigated areas^Footnote 67.

Erucastrum gallicum is recorded in NT, BC, AB, NB, NS, PE, and NF. Frankton and Mulligan (1987) state that it reaches its greatest abundance in MB and SK where it inhabits fields, waste areas, railways, gardens and orchards^Footnote 25. It is very common on road sides and is an abundant field weed in many localities in western Canada (Warwick and Wall, 1998). E. gallicum is within the Brassiceae tribe but has not been placed in the same clade as S. alba.

Lepidium draba is recorded in BC, AB, SK, MB, ON, QB, and NS. It is a perennial, rhizomatous plant that occurs in grain fields, hayfields, pasture grasses and legumes, ditches and roadsides. It is listed as a noxious weed in Canada^Footnote 68.

Raphanus raphanistrum is recorded in LB, NF, NS, PE, NB, QC, ON, SK, AB, and BC. It is an annual, winter annual or biennial that occurs in fields and pastures. It occurs in cultivated fields, abandoned fields, gardens, grasslands, meadows, orchards, woods, cliffs, riverbanks, beaches, dunes, roadsides, railway lines and disturbed areas. It is listed as a noxious weed in Canada^Footnote 69.

Sisymbrium altissimum (tumble mustard) is recorded in YK, NT, BC, AB, SK, MB, ON, QC, NB, NS, PE, and NF. It is an annual that occurs on dry hillsides, fields, prairies, rangeland, pastures, high meadows, gardens, flats, wharves, roadsides, railways, and waste places.

Sisymbrium loeselii (tall hedge mustard) is recorded in BC, AB, SK, MB, ON, QC, and NB. It is an annual that occurs in dry cultivated fields, especially grain fields, prairies, rangelands, river banks, beaches, roadsides, railways, and waste places.

Sisymbrium officinale (hedge mustard) is reported in BC, AB, MB, ON, QB, NB, NS, and PE. It is an annual that occurs in open disturbed areas in fields, farmyards, gardens, lawns, streamsides, beaches, roadsides, railways, and waste places.

Thlaspi arvense is recorded in YK, NT, BC, AB, SK, MB, ON, QC, NB, NS, PE, NF, and LB. It is an annual or winter annual weed that occurs in fields (grain, hay, rape), gardens, rangeland, irrigated areas, sloughs, meadows, beaches, outcrops, roadsides, railways, and waste places.

Relatives not currently found in Canada:

Kremeriella and species from Hemicrambe and most species from Coincya are not recorded in North America^Footnote 70,^Footnote 71,^Footnote 72. Coincya monensis subsp. recurvata (star mustard) is an invasive species introduced to the United States from western Europe or northwestern Africa^Footnote 73. The species has spread quickly^Footnote 74 and is now reported in Michigan and Pennsylvania^Footnote 75. It is an annual or perennial^Footnote 76. It is a colonist of open habitats found in disturbed areas such as fields, trails and railroad tracks in rocky and gravelly areas^Footnote 76. It can also occur in maritime sands, sandy rivers, and cliffs, forming large dense stands that can exclude other species^Footnote 76.

5.1 Inter-species/genus hybridization

As described above, our understanding of the relatives that S. alba may hybridize with is incomplete. Compared to the number of species in the Brassicaceae family, relatively few have been tested for compatibility with S. alba. In addition to molecular research to better identify relatives of S. alba, experiments are needed to determine the potential for S. alba to hybridize with weedy relatives including, C. monensis, D. muralis, S. arvensis, R. raphanistrum, and E. gallicum. Based on available information, we cannot determine the potential for S. alba to hybridize with related species.

FitzJohn et al. (2007) reviewed hybridization within the Brassicaceae family and found that most reported cross combinations were unsuccessful, and most crosses have only been reported once^Footnote 77. Where crosses were successful, rates of hybrid production were typically very low. No reports were found of successful hybridization under natural conditions between S. alba and any other species^Footnote 78,^Footnote 79.In rare cases, hand pollination was used to produce some hybrid offspring^Footnote 80,^Footnote 81 (see Table 1). S. alba has a diploid chromosome number of 2n = 24, meaning it has 2 sets of 12 chromosomes (1 from the paternal parent and 1 from the maternal parent). Many of the related species do not share the same number of chromosomes as S. alba and this will reduce sexual compatibility^Footnote 18. However, there are examples of successful crosses between species in the Brassicaceae family with different chromosome numbers^Footnote 47.

In almost all cases where hybrids were obtained between S. alba and species from the Brassicaceae family, one of the following methods was used to overcome sexual incompatibility (see Table 2):

• sexual crosses combined with in vitro techniques, for example, ovary culture and embryo rescue
• somatic hybridization by protoplast fusion^Footnote 78

Hybridization with other crop species

S. alba contains many agronomic traits that are of interest to breeding programs for related species, including insect and disease resistance. There have been many efforts to cross S. alba with species including B. napus, B. carinata, R. sativus, B. nigra, B. oleracea, and B. juncea (see Table 1 and Table 2).

Hybridization with related weeds and wild species

Compared to crop species, less effort has been placed on creating S. alba hybrids with weed species. FitzJohn et al. (2007) found no reported cases of attempted hybridization between S. alba and any non-crop species^Footnote 77. S. arvensis is the only other species in the Sinapis genus found in Canada, and it is a troublesome weed. No reports of naturally occurring hybrids between S. arvensis and S. alba hybrids were found in the literature^Footnote 82. Nelson (1927) reported sterile hybrids from crosses between S. alba and charlock (a common name for S. arvensis), which produced small pods with no seeds^Footnote 9. S. alba has 2n = 24 chromosomes, while S. arvensis has 2n = 18 chromosomes^Footnote 83. This difference will reduce the likelihood of viable hybrids between these species. However further research is needed to confirm that S. arvensis and S. alba do not hybridize under field conditions.

Studies would be useful to assess the potential for gene flow between S. alba and:

• D. muralis (2n = 42)
  • D. muralis is a recently formed allopolyploid and a widespread weed in Canada
  • This may increase the likelihood of hybridization with additional taxa
  • Successful conventional crosses have been made between D. muralis and both B. napus (AC and genomes^Footnote 84) and B. rapa (A genome^Footnote 77)
• C. monensis (2n = 24, 48)
• S. arvensis (2n = 18)
• R. raphanistrum (2n = 18)
  • R. raphanistrum is within the Brassiceae tribe but has not been placed in the same clade as S. alba
  • However, following genetic analyses Raphaninae genera and S. alba have been included in the nigra lineage, suggesting that intergeneric hybridization may be possible^Footnote 55
• E. gallicum (2n = 30)

5.2 Potential for introgression of genetic information from S. alba into relatives

S. alba contains many agronomic traits that may contribute to breeding programs for related species, including insect and disease resistance. There have been many efforts to cross S. alba with other cultivated species. Despite this, successful gene introgression has only been demonstrated into B. napus for yellow seed colour^Footnote 96,^Footnote 99.

An OECD report concluded that the possibility of introgression from S. alba to B. napus under natural conditions is extremely low^Footnote 47.

No reports of naturally occurring gene flow between S. alba and other crops, weeds, or wild species were found in the literature. The potential for introgression of genetic information from S. alba into wild relatives is undetermined.

6. Potential interaction of S. alba with other life forms

The interactions of S. alba with other life forms in Canada have not been extensively studied in agricultural environments. Naumkin and Velkova (2013) identify and quantify insect pollinators in Russian S. alba fields^Footnote 31. Information on the management of many diseases and insect pests of S. alba can be found in provincial publications^Footnote 7,^Footnote 15,^Footnote 37.

S. alba is resistant, or has some tolerance, to some insect pests and diseases. However, damage may still occur depending on pest pressure, timing, and whether other stressors are present. Diseases S. alba is resistant or tolerant to include:

• Alternaria diseases (moderate tolerance only)^{Footnote 100}
• Heterodera schachtii (beet cyst nematode)^{Footnote 101}

and insect pests include:

• cabbage seedpod weevil (Ceutorhynchus obstrictus)^Footnote 15,^{Footnote 102}
• flea beetles^Footnote 15,^{Footnote 103}
• aphids^{Footnote 102}

The most common diseases of S. alba in Canada include:

• damping off (Phytophthora cactorum and/or Pythium spp.)
• wirestem and brown girdling root rot (Rhizoctonia solani)
• Sclerotinia white mold (Sclerotinia sclerotiorum)
• white rust/staghead (Albugo candida)
• Alternaria diseases: black spot, gray leaf spot, and pod spot (Alternaria brassicae and/or Alternaria brassicola)
• white leaf spot/grey stem (Mycosphaerella capsellae)
• aster yellows (aster yellows phytoplasma)
• clubroot (Plasmodiophora brassicae)^Footnote 7,^Footnote 15

Insect pests of S. alba include:

• cutworm
• grasshoppers
• diamond back moth (Plutella xylostell) (does not overwinter in Canada)
• Bertha armyworm (Mamestra configurata)^Footnote 7,^Footnote 15,^{Footnote 102}

Please refer to the tables below for examples of interactions of S. alba with other life forms during its life cycle:

• Table 3: Fungi
• Table 4: Chromist
• Table 5: Phytoplasma
• Table 6: Insects
• Table 7: Animals
• Table 8: 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