The Biology of Brassica rapa L.
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Biology Document BIO1992-02: A companion document to the Directive 94-08 (Dir94-08), Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits
Table of Contents
Part A - General Information
Part B - The Biology of B. rapa
- B1. General Description and Use as a Crop
- B2. The Centres of Origin of the Species
- B3. The Reproductive Biology of B. rapa
- B4. Brief Outlook of Agronomic Practices for the Oleiferous B. rapa
- B5. Cultivated B. rapa as a Volunteer Weed
- B6. Summary of B. rapa Ecology
Part C - The Close Relatives of B. rapa
- C1. Inter-Species/Genus Hybridization
- Table 1. Interspecific and Intergeneric Hybrids obtained sexually between
B. rapa and those related species that are present in Canada
- C2. Potential for Introgression from cultivated B. rapa into Relatives
- C3. Occurrence of B. rapa and Related Species in Canada
- C4. The Agro-Ecology of Weedy Relatives of B. rapa
Part D - Potential Interactions of B. rapa with Other Life Forms
Part E - Bibliography
Part A - General Information
The Canadian Food Inspection Agency (CFIA) is responsible for regulating the field testing in Canada of agricultural and horticultural crop plants with novel traits (PNTs). PNTs are defined as a plant variety/genotype possessing characteristics that demonstrate neither familiarity nor substantial equivalence to those present in a distinct, stable population of a cultivated species in Canada and that have been intentionally selected, created or introduced into a population of that species through a specific genetic change. Familiarity is defined as the knowledge of the characteristics of a plant species and experience with the use of that plant species in Canada. Substantial equivalence is defined as the equivalence of a novel trait within a particular plant species, in terms of its specific use and safety to the environment and human health, to those in that same species, that are in use and generally considered as safe in Canada, based on valid scientific rationale. Environmental safety assessment criteria include:
- potential of the PNT to become a weed of agriculture or be invasive of natural habitats;
- potential impact of the PNT or its gene products on non-target species, including humans;
- potential for gene-flow to wild relatives whose hybrid offspring may become more weedy or more invasive;
- potential for the PNT to become a plant pest; and,
- potential impact on biodiversity.
The PNTs may be developed using traditional plant breeding techniques or other methodologies such as recombinant DNA technologies. Regulated field testing is necessary when PNTs are: (1) considered unfamiliar when compared with products already in the market; (2) not considered substantially equivalent to similar, familiar plant types already in use, and regarded as safe.
Before PNTs may be authorized for unconfined release, they must be assessed for environmental safety. Directive 94-08 (Dir94-08), entitled "Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits", describes the criteria and information requirements that must be considered in the environmental assessment of PNTs to ensure environmental safety in the absence of confined conditions.
The present document represents a companion document to Dir94-08. It is intended to provide background information on the biology of Brassica rapa L., its centres of origin and related species. Emphasis has been placed on detailing potential hybridization events between B. rapa and its close relatives. Discussion is limited to hybridization events that can occur in nature and result in fertile offspring.
Such species-specific information will serve as a guide for addressing some of the requirements of Part D of Dir94-08. Specifically, it will be used to determine if there are significantly different/altered interactions with other life forms resulting from the PNTs novel gene products which could potentially cause the PNT to become a weed of agriculture, become invasive of natural habitats, or be otherwise harmful to the environment.
The conclusions drawn in this document about the biology of B. rapa relate only to plants of this species with no novel traits.
Part B - The Biology of B. rapa
B. rapa and B. campestris were first described as two species by Linnaeus, with B. rapa being the turnip form and B. campestris, the wild weedy form. Metzger in 1833 concluded that these were the same species and combined the taxa under the name B. rapa (Toxeopus et al., 1984).
B1. General Description and Use as a Crop
B. rapa belongs to the Cruciferae (Brassicaceae) family, also known as the mustard family. The name crucifer comes from the shape of flowers, with four diagonally opposite petals in the form of a cross.
B. rapa has green foliage, leaves glabrous or slightly hispid when young, and the upper leaves partially clasping the stem. The stems are well branched, although the degree of branching depends on biotype / variety and environmental conditions. Branches originate in the axils of the highest leaves on the stem, and each terminates in an inflorescence. Lower leaves are sparingly toothed or pinnatifid and petioled, while upper leaves are sessile, subentire, oblong lanceolate and often constricted above the base. The inflorescence is an elongated raceme, the flowers are pale yellow, densely clustered at the top with open flowers borne at or above the level of terminal buds, and open upwards from the base of the raceme (Downey et al., 1980).
There are three well defined groups of B. rapa (A genome, n=10), based on their morphological characteristics: (1) the oleiferous or oil-type rape, often referred to in Canada as Polish rape or summer turnip rape, of which canola is a specific form having low erucic acid in its oil and low glucosinolate content in its meal protein; (2) the leafy-type B. rapa, including the chinensis group (pak-choi, celery mustard), the pekinensis group (Chinese cabbage), and the perviridis group (tendergreen); and (3) the rapiferous-type B. rapa, comprising the rapifera group (turnip, rapini), and the ruvo group (turnip broccoli, Italian turnip) (Hortus Third, 1976; Prakash and Hinata, 1980). The turnip and vegetable types are important as vegetable sources in many parts of the world and are used as forages for sheep and cattle. This document is written for the oleiferous rape.
B. rapa can be subdivided into: (1) Indian forms; ssp. trilocularis (Roxb.) Hanelt. known as yellow sarson and ssp. dichotoma (Roxb.) Hanelt. known as both toria and brown sarson, and; (2) western European and north American form; B. rapa ssp. oleifera (DC.) Metzg. (Kimber and McGregor, 1995).
The exact time and place of domestication are unknown, but Indian Sanskrit writings of 2000 to 1500 B.C. refer directly to oilseed rape and mustard, as do Greek, Roman and Chinese writings of 500 to 200 B.C. (Downey and Röbbelen, 1989). In Europe, domestication is believed to have occurred in the early middle ages and commercial plantings of rapeseed were recorded in the Netherlands as early as the 16th century. At that time rapeseed oil was used primarily as an oil for lamps. Later it became used as a lubricant for steam engines. Although used widely as an edible oil in Asia, only through breeding for improved oil quality, and through the development of improved processing techniques, has rapeseed oil become important in western nations. Since the Second World War, as a result of improved oil and meal quality, rapeseed production in Europe and Canada has increased dramatically. China, India, Europe and Canada are now the top producers, although there is potential for the crop to be successfully grown in the United States, South America and Australia where annual production increased sharply over the last few years.
Today "double low" commercial varieties of both B. napus and B. rapa dominate the oilseed Brassica production area in developed countries. These "double low" varieties are characterized as having a very low (<1%) content of erucic acid in the fatty acid profile of the seed storage lipid and a very low content of glucosinolates (<18 µmoles per gram seed at 8.5% moisture) in their seed and meal. The term "canola quality" is normally applied to seed, oil and meal from such varieties.
B. rapa was the dominant species in western Canada in the early 1970's (Downey et al., 1974). Similar acreages of B. napus and B. rapa were grown on the prairie provinces in the late 1980's but in the 1990's the proportion of the production area sown to B. rapa diminished to about 15 to 20%. The main B. rapa production regions in Canada are the province of Alberta, the Peace River region of British Columbia and northern Saskatchewan. The Manitoba acreage is primarily B. napus. B. rapa withstands spring frosts better than B. napus and generally requires fewer frost-free days to complete it's life cycle. B. rapa varieties therefore tend to be grown north of the areas in which B. napus is grown. Both spring and winter annual forms occur but only spring forms are grown. The winter forms are more productive than the spring forms but are not sufficiently winter hardy to be grown in Western Canada (Downey and Röbbelen, 1989).
B2. The Centres of Origin of the Species
Wild B. rapa ssp. oleifera [includes var. sylvestris] is regarded as the species from which var. rapa L. (cultivated turnip) and var. silvestris (Lam.) Briggs (turnip-rape) originated. It is native throughout Europe, Russia, Central Asia and the Near East (Prakash and Hinata, 1980), with Europe proposed as one centre of origin. The Asian and Near Eastern type may have originated from an independent centre of origin in Afghanistan which then moved eastward as it became domesticated. Prakash and Hinata (1980) suggest that oleiferous B. rapa developed in two places giving rise to two different races, one European and the other Asian. Recent evidence (Song and Osborn, 1992) through analyses of chloroplast and mitochondrial DNA suggests that B. montana (n = 9) might be closely related to the prototype that gave rise to both cytoplasms of B. rapa and B. oleracea.
Typically, the range of B. rapa extends to coastal lowlands, plateaus, hills, and montane areas up to 2300 m (Warwick & Francis, 1994). In Europe, the winter form has become a common yellow crucifer of roadsides, waste and cultivated ground, docks, cities and towns, arable fields and riverbanks. In the British Isles, for instance, it has escaped from cultivation and is naturalised wherever oil-seed rape is grown. It is a relatively recent introduction into Canada and the United States, and is described as an occasional weed, escape or volunteer in cultivated fields (Munz, 1968; Muenscher, 1980). In Canada, it is found in disturbed habitats, typically in crops, fields, gardens, roadsides and waste places (Warwick and Francis, 1994).
B3. The Reproductive Biology of B. rapa
B. rapa, with the exception of the Indian yellow sarson form, is an obligate outcrosser due to the presence of self-incompatible genes. As a result, little or no seed is set when B. rapa is self-pollinated. B. rapa pollen is sticky but lighter than that of B. napus (K. Falk and K. Downey, personal communications). As with B. napus, relatively high pollen levels can result from synchronously blooming B. rapa fields and the concentration of pollen, as indicated by outcrossing studies, decreases rapidly with increasing distance from the source of pollen (Stringam and Downey, 1978; Raney and Falk, 1998). Under field conditions, B. rapa pollen is transferred from plant to plant primarily through physical contact between neighbouring plants. It can be also transferred over longer distance by wind and insects. To minimize contamination of B. rapa foundation seed plots, a distance of 400 metres is required from other contaminating source of B. rapa pollen (CSGA, 1994).
Pollinating insects, in particular honey bees (Apis mellifera) and bumble bees (Bombus sp.), are believed to play a major role in the transfer of pollen over long distances. The dynamics of bee mediated pollen movement depend on the quantity of pollen available (size and density of donor population), the relative size, location and direction of the receiving populations from the pollen source, as well as on the environmental conditions and insect activity (Levin and Kerster, 1969; Ellstrand et al., 1989; Klinger et al., 1992; Stringam and Downey, 1978; Raney and Falk, 1998). Generally, the weather conditions at flowering time will influence pollination, for example a reduction in bee activity on cold or windy days.
B4. Brief Outlook of Agronomic Practices for the Oleiferous B. rapa (based on Thomas, 1994)
The spring-type oleiferous B. rapa is a cool-season crop. It is widely adapted, and performs well in a range of soil conditions, provided that moisture and fertility levels are adequate. Air and soil temperatures influence canola plant growth and productivity. The optimum temperature for maximal growth and development is just over 20°C, and it is best grown between 12°C and well below 30°C. After emergence, seedlings prefer relatively cool temperatures up to flowering; high temperatures at flowering will hasten the plant's development, reducing the time from flowering to maturity.
B. rapa is commonly swathed at physiological maturity when 30-50% of the seeds on the plant have begun to turn from green to brown or yellow. The seed is combined at full maturity when nearly all the seeds have turned colour. The use of desiccants results in rapid and more uniform maturity thus allowing the crop to be straight combined. Furthermore, B. rapa is more resistant to shattering compared to B. napus making B. rapa easier to straight combine.
Agronomic practices of B. rapa are influenced by the increased awareness of soil conservation issues. Minimal or no till B. rapa production are recommended, where most of the crop residue and stubble are left on the soil surface to trap snow, reduce snow melt run-off, stop wind and water erosion of the soil, and increase soil water storage. Reduced tillage techniques, however, are only effective when they are combined with a good systematic weed control program.
Weeds can be one of the most limiting parameters in rapeseed production. The closely related cruciferous weeds, e.g. wild mustard (Sinapis arvensis), stinkweed (Thlaspi arvense), shepherd's purse (Capsella bursa-pastoris), ball mustard (Neslia paniculata), flixweed (Descurainia sophia), wormseed mustard (Erysimum cheiranthoides), hare's-ear mustard (Conringia orientalis), common peppergrass (Lepidium densifolium), etc. are often problematic. Spring-type oilseed rape does not compete well with weeds in the early growth stages, because it is slow growing and slow to cover the ground. Weeds must be controlled early to avoid yield loss due to competition. Although the crop can be attacked by a number of insect pests, insect control must be carefully designed to reduce unnecessary and costly pesticide applications, opportunities for resistance buildup in insects, and damage to honeybees and native pollinating insects. Diseases can be severe in large production areas, and are greatly influenced by cultivation practices and environmental factors. To control disease, growers are advised to implement disease management programs (please refer to Table 2 for examples of B. rapa pests and diseases).
Generally, Brassica species should not be grown on the same field more often than once every four years, to prevent the buildup of diseases, insects, and weeds. Chemical residues from herbicides and volunteer growth from previous crops including rapeseed crops grown for different oil types are also important factors to consider when selecting sites.
Breeding of B. rapa is commonly done using simple recurrent selection procedures to prevent inbreeding depression. B. rapa shows considerable heterosis for yield, with up to 40% yield increases and there is consequently a strong interest in developing hybrid or synthetic cultivars (Falk et al., 1998). Synthetic cultivars are the result of random matings between selected parental lines, which give rise to both hybrids and progeny (sibs) from matings within the same parental lines (Buzza, 1995; Falk et al., 1998). The first B. rapa synthetics were registered in Canada in May 1994 under variety names CASH, Hysyn 100 (Falk and Stoenescu, 1996a), Hysyn 110 (Falk and Stoenescu, 1996b) and Maverick (CFIA, 1999).
B5. Cultivated B. rapa as a Volunteer Weed
As with all crops cultivated and harvested on a field scale, some seeds may escape harvest and remain in the soil until the following season when they germinate either before or following seeding of the succeeding crop. In some instances the volunteers may give considerable competition to the seeded crop and cause deterioration of quality of the crop harvest. In such instances, chemical and/or mechanical control is essential.
The problem of volunteer plants in succeeding crops is common to most field crop species. Much depends on the management practices used in the production of the crop, i.e. whether the plants have disbursed seed at the time of harvest, the setting of the harvesting equipment, and speed of the harvesting operation which will determine whether more or less seed is lost by the harvester. Brassica crops produce large numbers of small sized seed, which without proper management practices can result in severe volunteer problems in succeeding crops. Similar problems may be encountered with cultivated B. juncea and B. napus varieties. Shattered seeds of B. rapa can be induced to become dormant, especially if buried in the soil, although a suitable soil treatment after the harvest can considerably reduce the volunteer problem.
B6. Summary of B. rapa Ecology
B. rapa is a plant of disturbed habitats. In unmanaged ecosystems this species may be considered a primary colonizer, i.e. a plant species that is the first to take advantage of disturbed land where they would compete against plants of similar types for space. Unless the habitats are disturbed on a regular basis, such as on cliff edges, river edges and the edges of pathways made by animals, populations of these types of plants will become displaced by intermediaries and finally by plants that will form climax ecologies such as perennial grasses on prairies, and tree species and perennial shrubs in forests.
There is potential for B. rapa to become naturalized in disturbed habitats, such as roadsides, industrial sites, waste places, and crop lands. Evidence for this can be found in the plant records of B. rapa from countries where B. rapa has been introduced as a crop plant. The ability of B. rapa to compete for space with other primary colonizers will affect whether it becomes naturalized in a particular area. This will also be dependent on the suitability of the climate, soil conditions, etc. of that area.
In crop production systems, poor management practices and insufficient resistance to pod shattering may cause a large reduction in the numbers of seed of B. rapa harvested. This may, especially at high crop densities, cause volunteer weed problems in succeeding crops and also contamination of such crops with respect to their seed quality, especially if they are present at high density.
B. rapa is not listed as a noxious weed in the Weed Seed Order (1986). Weeds of Canada (Frankton and Mulligan, 1993) reports that B. rapa is distributed widely across all provinces in Canada. Field research shows that B. rapa occurs largely as a volunteer weed in cultivated land in the Western provinces (Thomas and Frick, 1998; Thomas et al., 1998). Reports of B. rapa as a weed are more frequent in Québec and in the eastern provinces of Canada. In the corn fields of eastern Canada where continuous use of the herbicide Atrazine was employed, selection pressure resulted in the identification of B. rapa plants tolerant to the triazine family of herbicides (Maltais and Bouchard, 1978). Additionally, bird rape, a wild B. rapa biotype, is a minor weed in limited grain field acreages in Ontario (Alex and Switzer, 1976).
Part C - The Close Relatives of B. rapa
C1. Inter-Species/Genus Hybridization
In considering the potential environmental impact following the unconfined release of genetically modified B. rapa, it is important to have an understanding of the potential for development of hybrids through interspecific and intergeneric crosses between the crop and its related species. The development of such hybrids could result in the introgression of the novel traits into these related species and result in:
- the related species becoming more weedy in agriculture lands or invasive of natural ecosystems; and,
- altered environmental interactions potentially causing harm to the environment or to human health and safety.
For a trait to become incorporated into a species genome, it is first necessary for hybrid intermediaries to be produced, and secondly that recurrent backcrossing of plants of that species to hybrid intermediaries occur, and for the resulting progeny to be viable and capable of reproducing.
While interspecific and intergeneric crosses have been made between B. rapa and its relatives, many have necessitated intervention in the forms of ovary culture, embryo rescue and protoplast fusion. Reported in the literature and cited below in Table 1 are interspecific and intergeneric hybrids that were obtained by sexual matings between B. rapa and related species that are present in Canada (Warwick and Black, 1993; Prakash and Hinata, 1980).
Table 1. Interspecific and Intergeneric Hybrids obtained sexually between B. rapa and those related species that are present in Canada
|B. napus x B. rapa||F1, F2, BCP||Morinaga, 1929; U, 1935; Bing et al.,
1991; Jørgensen & Andersen, 1994; Mikkelsen et al., 1996
|B. rapa x B. napus||F1, F2, BCP||Morinaga, 1929; U, 1935; Bing et al., 1991;
Falk, 1991; Jørgensen & Andersen, 1994; Mikkelsen et al., 1996
|B. rapa x B. nigra||F1||Mizushima, 1950; Prakash, 1973; Hinata et al., 1974;
Mattsson, 1988; Bing et al., 1996
|B. nigra x B. rapa||F1||Hinata et al., 1974|
|B. rapa x B. oleracea||F1||Wojciechowski, 1985; Mattsson, 1988|
|B. oleracea x B. rapa||F1||Ellerström, 1978; Wojciechowski, 1985|
|B. rapa x B. carinata||F1||Takeda, 1975; Falk, 1991|
|B. carinata x B. rapa||F1||Mizushima, 1950|
|B. juncea x B. rapa||F1, BCP||Sinskaia, 1927; Olsson, 1960;
Katiyar and Chamola, 1995
|R. sativus x B. rapa||F1||Ellerström, 1978|
|B. rapa x S. arvensis||F1||Mizushima, 1950|
|Diplotaxis erucoides x B. rapa||F1||Hinata et al., 1974; Vyas et al., 1995|
|D.. muralis x B. rapa||F1||Salisbury, 1989; Lefol et al., 1997|
|D. tenuifolia x B. rapa||F1||Salisbury, 1989|
|B. rapa x Erucastrum gallicum||F1||Lefol et al., 1997|
Some hybrids, such as the B. rapa x B. napus, B. napus x B. rapa and B. rapa x B. nigra hybridizations, resulted from field outcrossing studies reported by Bing et al. (1991, 1996). Others were achieved through hand pollination, usually through emasculation of the female plant followed by transfer of pollen from the male plant using a paint brush.
Interspecific crosses may result in progeny that exhibit partial fertility/sterility. This may be influenced by the chromosome number of the cultivated species and relatives. Many hybrids fail to occur due to a lack of development of the endosperm (tissue resulting from the fertilization of the two polar nuclei of the embryo sac by a male reproductive nucleus). Although there are many exceptions, a 2:1 ratio, or higher, of maternal and paternal chromosomes improves the chance for a successful cross (Nishiyama and Inomata, 1966). For example, the pollination of a tetraploid female parent by a diploid male usually produces seed while the reciprocal cross is less productive or produces no seed. Also of interest is the finding that partially fertile plants produced by the interspecific cross, B. napus x B. rapa, are able to set seed upon selfing.
Flowering periods of B. rapa and other species, such as B. napus, B. nigra, are critical for hybridization events to occur. Flowering periods, which are largely environmentally influenced, must overlap at least partially. To evaluate hybridization potential, it is important to know the flowering chronology of both the cultivated plant and related species, physical distance between species with potential to hybridize; occurrence of vectors for pollination, and in the case of pollination by insects, the frequency of the potential pollination, activity and behaviour.
For a trait to become incorporated into a species genome, recurrent backcrossing of plants of that species by hybrid intermediaries, and survival and fertility of the resulting offspring, is necessary.
C2. Potential for Introgression from cultivated B. rapa into Relatives
The hybridization events listed in Table 1 are intended to assist the assessment of the potential for introgression of novel traits introduced from cultivated B. rapa into wild relatives. Several factors should be considered when evaluating the potential of gene flow from one species to another, including: cross compatibility of the species involved; direction of the cross; viability of the seed developed from the interspecific or intergeneric cross; and fertility of the hybrid. The probability of gene transfer cross the Brassicas is quite high due to the cross-compatibility of the members of the triangle of U.
The first step in this assessment is to determine which, if any, of the potential mates of B. rapa are recorded as present in the geographic region where the cultivation is proposed. Should there be potential wild relative mates present, the frequency of hybridization events and the potential for environmental impact should introgression occur would then be considered.
Wild populations of B. rapa (bird rape) exist in agricultural sites and gene flow from B. rapa crop plants to these individuals is likely to occur.
Bing et al. (1991) suggested that of the crosses they attempted, there was potential for hybrids between B. napus, B. juncea and B. rapa to produce viable seed that could survive to the next generations. These three species are widely grown as crops for the production of both canola and mustard.
S. arvensis is perhaps the worst of the weedy Brassica relatives, especially in the major canola growing areas of Manitoba, Saskatchewan and Alberta. It presence was recorded as high as 45% in surveyed canola fields in Manitoba (Thomas et al., 1998).
Hybrid combinations successfully created using B. rapa as a female parent may be relevant to gene flow considerations as they could act as genetic bridges to other related Brassica species. Of concern would be the role of B. juncea as a genetic bridge to either B. nigra or S. arvensis, as B. juncea can hybridize with both of these species (Bing et al., 1991).
C3. Occurrence of B. rapa and Related Species in Canada
Of the above listed crosses, B. carinata is not reported as present in Canada (Warwick, 1993; Warwick et al., 1999), although it may provide a future source of genes responsible for large yellow seeds, disease and pod shattering-resistance for canola breeding. There are only old records of D. erucoides reported in the Gaspé peninsula of Québec. B. oleracea, apart from the wild types in their original habitats in Europe, is rarely found outside of cultivation.
Of the other species:
- The wild form of B. rapa (bird rape) is recorded in the Northwest Territories, District of Mackenzie (NT-M), Yukon Territory (YT), Labrador (LB), Newfoundland (NF), Nova Scotia (NS), Prince Edward Island (PE), New Brunswick (NB), Québec (PQ), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB) and British Columbia (BC). Weeds of Canada (Frankton and Mulligan, 1993) suggests it is sometimes abundant and that in some parts of Eastern Canada, bird rape supplants S. arvensis over large areas. Alex and Switzer (1976) indicate it occurs in a few grainfields and waste areas in Southern Ontario;
- B. napus (rapeseed) is recorded in the NT-M, LB, NF, PE, NS, NB, PQ, ON, MB, SK, AB and BC. B. napus is not listed in Weeds of Canada (Frankton and Mulligan, 1993) nor in Ontario Weeds (Alex and Switzer, 1976).
- B. juncea (oriental mustard and brown mustard) is recorded in NT-M, NF, NS, PE, NB, PQ, ON, MB, SK, AB and BC. Weeds of Canada reports that it occurs in every province and reaches its greatest abundance in the western provinces. Ontario Weeds indicates its distribution is similar to that of S. arvensis although it is generally less common;
- B. nigra (black mustard) is recorded in NF, NS, PE, NB, PQ, ON, SK, and BC. Weeds of Canada suggests that it is not very common in western Canada. In Ontario Weeds it is listed as occurring in a few localities in the south of the province especially in fields and waste areas bordering river valleys, and along railways;
- D. muralis (sand rocket) is recorded in NS, PE, NB, PQ, ON, MB, SK, and AB. Weeds of Canada does not list this species. Ontario Weeds indicates it usually occurs in coarse soils along roads, railways, beaches and around buildings and waste places in Southern Ontario;
- D. tenuifolia (wall rocket) is recorded in NS, NB, PQ, and ON. It is a common perennial found along roadsides and in waste places (Crompton et al., 1988). Weeds of Canada does not list this species.
- E. gallicum is recorded in NT-M (Warwick and Wall, 1998), NF, NS, PE, NB, PQ, ON, MB, SK, AB and BC. Weeds of Canada states that it reaches its greatest abundance in Manitoba and Saskatchewan where it inhabits fields, waste places, railway yards, gardens, and orchards. It is very common on roadsides, and is an abundant field weed in many localities in Western Canada. In Ontario, it occurs throughout the province but is more common in southern Ontario where it is frequently found around railway yards, waste places, orchards, gardens, roadsides and occasionally in grainfields;
- Raphanus sativus (radish) is recorded in NT-M, NF, NS, PE, NB, PQ, ON, MB, SK, AB and BC. Weeds of Canada indicates that this species is occasionally persistent in gardens (as a result of cultivation) and in wild locations;
- S. arvensis (wild mustard) is recorded in NT-M, YT, LB, NF, NS, PE, NB, PQ, ON, MB, SK, AB and BC. Weeds of Canada lists it as one of the most common annual weeds. It occurs in all provinces where the most serious infestations are probably in the rich river valleys of the West. Its habitats include grainfields, cultivated fields, waste places, fence rows and roadsides. Ontario Weeds indicates that it occurs throughout Ontario being most frequent in cultivated fields and gardens but occasionally appearing in fence lines, along roadsides and in waste areas.
C4. The Agro-Ecology of Weedy Relatives of B. rapa
Of the relatives discussed, S. arvensis (wild mustard) is listed as a primary noxious weed in the Weed Seeds Order (1986) and is potentially the weediest in agricultural crop lands. It is relatively easily controlled in crops of species other than Brassica by the use of selective herbicides.
Weed species prominence can be dramatically affected by cropping systems and cultivation practices. The recent adoption of minimum and no till crop production systems, and the abandonment of cultivated summerfallow practices as a means of soil conservation, have caused a shift in the prominence of different weed species.
The weedy relatives of B. rapa are all plants of disturbed habitats, and the ecosystems in which they survive and flourish are as described in part C3. above. Their success will be dependent on their ability to compete for space with other primary colonizers, in particular, with other successful weedy plant types. This in turn will depend on how well suited they are to the particular climate, soil conditions, etc. of individual sites.
Part D - Potential Interactions of B. rapa with Other Life Forms
Table 2 is intended to guide applicants in their considerations of potential impacts the release of the PNT in question may have on non-target organisms, but should not be considered as exhaustive. Where the impact of the PNT on another life form (target or non-target organism) is significant, secondary effects may also need to be considered.
Table 2. Potential interactions of B. rapa with other life forms during its life cycle
|Other life forms||Interaction with B. napus
(Pathogen; Symbiont or Beneficial Organism; Consumer; Gene transfer)
(Light leaf spot)
(Basal stem rot, Damping off)
(Sclerotinia stem rot)
|Turnip mosaic virus||Pathogen|
|Aster yellows mycoplasma||Pathogen|
|Pollinators||Symbiont or Beneficial Organism; Consumer|
|Mychorrhizal fungi||Symbiont or Beneficial Organism|
|Soil microbes||Symbiont or Beneficial Organism|
|Earthworms||Symbiont or Beneficial Organism|
|Other B. rapa||Gene Transfer|
|B. napus||Gene Transfer|
|B. juncea||Gene Transfer|
|B. nigra||Gene Transfer|
|R. sativus||Gene Transfer|
|S. arvensis||Gene Transfer|
|D. erucoides||Gene Transfer|
|D. muralis||Gene Transfer|
|D. tenuifolia||Gene Transfer|
|E. gallicum||Gene Transfer|
Part E - Bibliography
Alex, J. F. and C. M. Switzer (1976). Ontario Weeds. Ontario Ministry of Agriculture and Food Publication 505. 200 pp.
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