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Chapter 1. Agronomic Improvement In Oilseed Brassicas

Chapter 1. Agronomic Improvement In Oilseed Brassicas

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2



R. K. D O W N E Y A N D S. R. RIMMER



1983; Scarisbrick and Daniels, 1986; Downey and Robbelen, 1989) have

dealt in detail with many aspects of oilseed Brussicu improvement, especially those which relate to improvements in fatty acid composition and

the reduction in levels of glucosinolates in the residual meal. Substantive

changes in the quality of seed oil and meal composition have resulted in

dramatic increases in areas of production in Canada and western Europe

(see below). Unfortunately, this has also resulted in a rather narrow germ

plasm base of cultivated oilseed brassicas, especially in Brussicu nupus L.

Emphasis in plant breeding has consequently shifted from quality improvement toward increasing seed yield, incorporating resistance to diseases and pests, and improving tolerance to stress. This review focuses on

recent developments and current and future trends for agronomic improvements in oilseed Brussicu crops.



A. WORLD

SOCIOECONOMIC

IMPORTANCEOF THE OILSEED

BRASSICAS

Historically, human consumption of vegetable oil obtained from Brussicu spp. was primarily concentrated in asiatic countries, predominantly in

the northern Indian subcontinent and in China. The cultivation in these

countries of oilseed types of Brussicu rupu L. (syn. Brussicu cumpestris L.)

and Brussicu junceu (L.) Czern. dates back to approximately 1500 BC

(Prakash, 1980), and these areas today are still major producers and consumers of Brussicu vegetable oils.

Since the second world war, a dramatic increase in Brussicu oilseed

production has occurred worldwide. In Canada and in Europe this was

associated with seed quality improvements through plant breeding involving the modification of the fatty acid composition (elimination of erucic

acid) and the reduction of glucosinolate content in the residual meal. The

large production increase in Europe was also related to economic support

from the Common Agricultural Policy of the European Economic Community (EEC). Thus, in the 1948- 1952 period, 70% of a world total

oilseed Brussicu production of 2.8 million tonnes was produced in Asia,

but by 1984, Canada (20%) and Europe (35%) produced more than half the

total world production of 15.9 million tonnes, with the Indian subcontinent ( 18%) and China (25%) producing the balance (Bunting, 1986). Total

world production values of oilseeds, edible vegetable oils, and residual

protein meals for the years 1985-1989 are given in Table I. Oilseed

brassicas account for approximately 10% of total world oilseed production

and 14- 15% of the total edible vegetable oil production. Production by the

primary producing regions of oilseed brassicas is shown in Table 11. Total

world production is now in excess of 20 million tonnes annually.



3



AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

Table I

World Production of Oilseeds, Edible Vegetnble Oils, and

Derived Protein Meals, 1985 - 1989a



Millions of t o n n e produced by years

Commodity



1985- I986



1986- 1987



1975- 19Mb



1988- 1989'



Oilseeds

Soybean

Cottonseed

Peanuts

Sunflowerseed

Rapeseed

Flaxseed

Coconut

Palm kernel



97.03

30.63

19.94

19.56

18.57

2.36

5.32

2.56



97.92

27.13

20.44

19.25

19.46

2.69

4.72

2.60



103.17

3 1.05

19.72

20.5 1

22.97

2.28

4.24

2.67



93.13

32.24

21.56

20.96

21.72

1.75

4.56

2.89



195.57



194.21



206.61



198.81



13.85

3.47

2.94

6.65

6.19

1.63

3.3 I

1.11

8.17



15.19

3.05

3.10

6.57

6.83

I .56

2.95

I .09

8.09



15.20

3.46

2.85

7.20

7.65

I .90

2.59

8.53



14.85

3.62

3.35

7.57

7.27

1.41

2.76

I .26

9.36



47.32



48.43



50.56



5 1.45



6 1.07



1.89

1.33



67.12

9.83

4.42

7.54

11.09

I .20

1.72

I .32



67.37

11.17

4.01

8.13

12.51

1.14

1S O

1.41



65.54

11.62

4.77

8.59

11.80

0.99

1.60

I .49



98.6 1



104.24



107.30



106.40



Total

Edible vegetable oils

Soybean

Cottonseed

Peanuts

Sunflowerseed

Rapeseed

Olive

Coconut

Palm kernel

Palm

Total

Protein meals

Soybean

Cottonseed

Peanuts

Sunflowerseed

Rapeseed

Flaxseed

Coconut

Palm kernel

Total



11.10



4.22

7.66

10.19

1.15



From United States Department of Agriculture, 1988.

Preliminary estimates.

'Forecast estimates.

a



1.18



R. K. DOWNEY AND S. R. RIMMER



4



Table 11

Production of Oilseed Brassicas by Main Producing Countries/Regions, 1982- 1989'

Millions of tonnes by years

Average

Country or region



1982/1983- 1986/1987



1987- 1988'



1988- 1989'



India

China

Canada

EEC

Europe (excluding EEC)

Other



2.64

5.13

3.1 I

3.18

I .70

1.06



3.10

6.61

3.85

5.95

2.16

1.31



3.50

5.04

4.24

5.3 I

2.18

1.45



16.82



22.98



21.72



Total



From United States Department of Agriculture, 1988.



'Preliminary estimates.

Forecast estimates.



B. Brcusica OILSEED

SPECIES

Four species of Brassica have been widely cultivated as oilseed crops,

Brassica carinata Braun, B. rapa, B. juncea, and B. napus. Where conditions are appropriate, namely cool temperate climates with good moisture

availability, winter forms of B. napus are preferred and are the most

productive. Most of the land area cultivated to oilseed brassicas in Europe

and China is sown to winter oilseed rape. However, as latitude or altitude

increases, the winter form of B. nupus is supplanted by the summer form of

B. napus or the winter or summer form of B. rapa. In Canada, cultivation

consists of approximately equal amounts of the summer types of these two

species.

Brassica juncea is well-adapted to drier conditions and is relatively fast

maturing. On the Indian subcontinent B. juncea is the dominant species

grown, although large areas are also sown to B. rapa types (toria and

sarsons) (Prakash, 1980). In these climates, with hot dry summers, nonvernalization types of oilseed brassicas are cultivated in the cool moist winter

season. Brassica juncea is also grown in many parts of China outside of the

Yangtse/Yellow river flood plains (Stinson et a!., 1982). In western Canada

B. juncea is grown as a crop for condiment on some 8 1,000 ha but has

strong potential as an oilseed crop for this region (Woods et al., 1991).

Brassica carinata may perform well under long season growing conditions.



AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS



5



Its distribution presently is largely confined to North East Africa, principally Ethiopia. Clearly, these oilseed crops are well adapted to many

different parts of the world.

1. Genomic Relationships



The genomic relationships among the four oilseed Brassica species are

well known [see Mizushima ( 1980), Olsson and Ellerstrom ( I 980), and

Downey and Robbelen (1989)l. Our modem understanding of these relationships was initiated by Morinaga and co-workers (Morinaga, 1934),

who provided cytological evidence to show that Brassicu nigra (n = 8; B),

Brassica oleracea (n = 9; C), and B. rapa (n = 10; A) are primary species

and that 8. carinuta ( n = 17; BC), B. junceu (n = 18; AB), and B. napus

(n = 19; AC) are amphidiploids resulting from crosses between corresponding pairs of the primary species. These relationships were later confirmed by U (1935), who succeeded in the artificial synthesis of B. napus

from crosses between the diploid species B. rapa and B. oleracea. Synthesis

of B. juncea and B. curinata has subsequently been accomplished by the

interspecific hybridization between B. nigra and B. rapa or B. oleracea [see

Downey et al. (1975) and Olsson and Ellerstrom (198O)J.

Understanding the relationship among these Brassicu species has enabled plant breeders to create synthetic amphidiploids and to transfer

useful agronomic characteristics from species to species through interspecific hybridization. No cultivars have as yet been released as a direct result

of artificial reconstitution of a species through interspecific crosses, although some desirable characteristics have been successfully transferred

from one species to another through artificially synthesized amphidiploids

that function as a “bridge.” For instance, the first double-low (low erucic

acid content in the oil and low glucosinolate content in the meal) strains of

turnip rape were developed from interspecific crosses among turnip rape

(B. rupa), rape (B. napus), and oriental mustard (B. junceu) (Downey et al.,

1975). Similarly, the development of low-glucosinolate B. juncea involved

interspecific hybridization of B. rapa and B. junceu (Love et al., 1990).The

transfer of resistance to blackleg disease from B. junceu to B. nupus (Roy,

1984) is another example.

In China and Japan, interspecific crosses between B. rupa and B. napus

have often been used to transfer characteristics such as early maturity,

cytoplasmic male sterility, self-incompatibility, and yellow seed coat, from

the former to the latter, and to broaden the genetic basis of B. nupus

through genome substitution (Liu, 1985).



6



R. K. DOWNEY AND S. R. R I M M E R



2. Plant and Seed Description



Brassica rapa (AA, 2n = 20) is one of the primary diploid species and

occurs wild in the high plateaus of the Irano-Turanian regon (Hedge,

1976), where it is well adapted to the cool, short season environment of this

area. This species has a high relative growth rate under cool temperatures

and can produce abundant seed. Both spring and winter forms are cultivated and the most cold-hardy cultivars of the oilseed brassicas occur

within this species. This species is considered to be of the seed vernalization

type. Full clasping of the upper leaves around the stem, the positioning of

the terminal buds below newly opened flowers, and a high ratio of beak to

pod length are characteristic of this species. Both dark- and yellow-seeded

types occur.

Brassica carinata (BBCC, 2n = 34) is the amphidiploid between B.

oleracea and B. nigra. It shows a slow steady growth, probably derived

from the B. oleracea genome. Leaves, which are generally waxy and light

green in color, are attached to the stem with a true petiole. Though seeds

are predominantly dark, some types have yellow seed. Cultivation is limited to the Ethiopian plateau and adjacent areas of east Africa. It is

currently under evaluation and shows promise agronomically in many

other parts of the world.

Brassica juncea (AABB, 2n = 36) is the amphidiploid of B. rapa and B.

nigra. It has a high leaf area ratio and a high relative growth rate, comparable to B. rapa (Sasahara and Tsunoda, 197 1 ). Asia, especially China, is rich

in variations of cultivated forms of this species. It is grown widely for oil in

the north Indian subcontinent and in various regions of China (Xinjiang

Autonomous Region, Szechuan). This species is also characterized by

having leaves with true petioles. Leaves vary considerably in shape but are

generally of a dark green coloration. Seeds may be dark or yellow and the

“bold” types from India have a large seed size. It has considerable potential

as an oilseed crop in many other parts of the world.

Brassica napus (AACC, 2n = 38) is the amphidiploid of B. rapa and B.

oleracea. The existence of a wild form of B. napus is uncertain; if it does

exist it will probably be found in the European-Mediterranean region

( McNaughton, 1976). Olsson (1 960) suggested that the amphidiploid B.

napus (genome AACC) might have arisen at different locations by hybridization of various forms of B. oleracea (genome CC) and B. rapa (genome

AA). Leaves of this species lack a true petiole as does B. rapa, but only

partial clasping of the stem occurs. Seeds are dark, generally larger than

those of B. rapa, and no natural yellow-seeded types are known. Development of a yellow seed form that is known to be associated with a thinner

seed coat (and thus reduced fiber content in the meal) is one of the current



AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS



7



objectives in many breeding programs. Production of oil in Europe from B.

nupus occurred as early as the thirteenth century, when it was used primarily as lamp oil (Appelqvist, 1972).

3. Mode of Pollination



Brussicu rupu is primarily a self-incompatible species, as are the other

diploid brassicas, although some types of B. rupu, e.g., yellow sarson, are

self-compatible. The self-incompatibility (SI) in cruciferous species is of

the homomorphic sporophytic type determined by a single S locus. About

50-60 alleles are known at the S locus in B. oleruceu (Nasrallah and

Nasrallah, 1989). The allelic interactions at the S locus are dominant,

codominant, or recessive depending on the alleles involved. This system

ensures that B. rupu is normally 100% outbreeding and consequently

breeding methodologies for this species are designed to take advantage of

this natural heterozygosity.

The amphidiploids, B. nupus, B. junceu, and B. curinutu, are normally

self-compatible species, though S alleles from B. rupu have been introduced into some genotypes of B. nupus in order to develop SI-based F,

hybrids. Such hybrids have recently been registered for commercial production in Canada. Generally, self-pollination occurs readily in the amphidiploid species and selfed seed may easily be obtained by enclosing the

flowering racemes in bags. Under field conditions, outcrossing, from pollination due to insects and wind, has been estimated to range from 5 to

15% (Huhn and Rakow, 1979)to about 27 to 35% (Olsson, 1952; Persson,

1956) in winter rape, 22 to 36% in summer rape (Persson, 1956; Rakow

and Woods, 1987), and 19% for B. junceu (Rakow and Woods, 1987).

4. Oilseed Quality Improvements



At present, cultivars of two species (B. nupus and B. rupu) have been

developed with both low-erucic and low-glucosinolate (double low, or

canola) quality, and these are now widely grown commercially. In North

America the term “canola” has been coined to describe cultivars that meet

specific requirements for erucic acid in the extracted seed oil (less than 2%

erucic acid as a percentage of total fatty acids) and aliphatic glucosinolate

content in the residual meal (less than 30 pmol g-I). [For a discussion of

the development of low-erucic acid cultivars of B. nupus and B. rupu and

the genetics of the inheritance of erucic acid in these species, see Stefansson

( 1983).] It is likely that canolaquality cultivars of B. junceu and perhaps B.

curinutu will be developed in the near future, and, if this occurs, it will

significantly influence the choice of oilseed Brussicu species in some areas.



Table I11

Fatty Acid Composition of Oilseed Brassicu Crops and Other Common Vegetable Oils



Fatty acid composition (%)"

CY2



Species, crop,

cultivar, and type

Brussicu nupus (rape)

Victor winter

Jet Neuf winter

Hero summer

Westar summer

Stellar summer

Brussicu rupu (turnip rape)

Duro winter

Yellow sarson

Echo summer

Tobin summer

Brussicu junceu (mustard)

Indian origin

Cutlass



Ref!



14:O



16:O



16:l



18:O



18:l



18:2



18:3



20:O



20:l



22:O



22:l



24:O



0.3

0.4

0.2

0. I

tr



0.8

1.4



9.9

56.4

12.9

57.7

59.1



13.5

24.2

12.2

20.8

28.9



9.8

10.5

9.0



0.6

0.7

0.8

0.6

0.5



6.8

1.2

7.5

1.4

1.4



0.7

0.3

0.8

0.3

0.4



53.6

0.0

50.2

0.5

0.1



0.0

0.0

0.3

0.3

0.2



13.4

12.0

18.8

24.0



9.1

8.2

8.9

10.3



0.7

0.9



9.6

6.2

12.0

1.0



0.2

0.0

0.0

0.1



49.8

55.5

23.5

0.3



0.0

0.0



1.2



12.9

13.1

32.5

58.6



1.2

1.2



8.0

17.2



16.4

21.4



11.4

14.1



6.4

11.4



1.2

0.4



46.2

25.8



1



0.0



2

3

4

4



0.0

0.0

0.0

0.0



3.0

4.9

2.8

3.6

4.1



I

2

2

2



0.0

0.0

0.0

0.0



2.0

1.8

2.5

3.8



0.2

0.2

0.2

0.1



5

6



0.0

tr



2.5

3.3



0.3

0.3



1.O



1.6

I .4

I .o



0.9



1.O



11.5



3.3



0.6

0.6

1.2

0.1



0.0

0.0

0.1



0.2



24:l

1 .o



0.0

1.2

0.0

0.0

1.1



1.2

0.0

0.0

I .9

1.7



2km 1



2



tr



3.6



0.4



2.0



45.0



33.9



11.8



0.7



1.5



0.3



0.1



0.2



0.5



6



tr



3.2



0.2



0.9



9.8



16.2



13.9



0.7



7.5



0.7



41.6



0.6



2.0



7



0.0



15.3



0.0



4.2



23.6



48.2



8.7



0.0



0.0



0.0



0.0



0.0



0.0



8



0.1



5.8



0.1



5.2



16.0



71.5



0.2



0.2



0.1



0.7



0.0



0.1



0.0



9

9



9.2

6.7



0.0

0.0



0.0

0.0



3.1

4.3



57.2

71.4



23.4



0.0

0.0



1.4

1.6



1.4

1.0



2.6

2.7



0.0



11.1



0.0



1.8

1.3



0.0

0.0



10



tr



11.5



0.0



2.2



26.6



58.7



0.8



0.2



0.0



0.0



0.0



0.0



0.0



11



0.0

1.0



7.6

23.4



0.0

0.8



2.0

2.5



10.8

17.9



79.6

54.2



0.0

0.0



0.0

0.0



0.0

0.0



0.0

0.0



0.0

0.0



0.0

0.0



0.0

0.0



Brassicu carinafa

Ethiopian mustard

Glycine may (soybean)

Group 1 variety

Helianrhus annuus (sunflower)

Peredovik

Arachis hypoguea (peanut)

Virginia Bunch

Cook Jumbo

Zea mays (corn)

United States sources

Curlhamus finctorius (safflower)



us10

Gossypium hirsutum (conon)



12



Fatty acids represented by carbon chain length and number of double bonds; tr, trace amounts.

References: (1) Appelqvist (1969), (2) Downey (1983), (3) R.Scarth (unpublished), (4) Scarth ef al. (l988), (5) Appelqvist (1970). (6) R. K. Downey

(unpublished), (7) Hymowitz ef al. (1972), (8) Earle ef ul.(1968). (9) Worthington and Hammons (1971), (10) Beadle ef al. (1965), ( 1 1) Knowles (1968).

and ( 1 2) Anderson and Worthington (197 1).

a



10



R. K. DOWNEY AND S. R. RIMMER



In developed countries, the production of edible oil from oilseed brassicas

is now obtained exclusively from low-erucic acid cultivars and this trend is

expected to continue for production in developing countries.

Low-erucic acid strains of B. juncea have been recently obtained. These

strains were obtained by crossing plants from an accession with intermediate levels of erucic acid content and screening for low erucic acid in the

F, progeny using the half-seed technique (Kirk and Oram, 1981). The

development of low-glucosinolate B. junceu required interspecific hybridization of B. rupu and B. juncea (Love el ul., 1990) in order to transfer the

Bronowski block for aliphatic glucosinolate synthesis from a B. rupu line

producing low glucosinolate to a strain of B. juncea that produced 3-butenyl glucosinolate but no 2-propenyl (allyl) glucosinolate.

Continued improvement for oilseed quality includes development of

strains with modified fatty acid composition. These include development

of strains with lower levels of linolenic acid, higher levels of linoleic acid,

high oleic acid levels, and other modifications (see Table 111 for a comparison of the fatty acid compositions of oilseed brassicas and other vegetable

oilseed crops). A cultivar with low levels of linolenic acid (<4%) has been

developed and registered in Canada (Scarth el ul., 1988). The oil with

reduced levels of linolenic acid from this cultivar has been shown to have a

prolonged cooking and shelf life (Kay, 1988). Oilseed brassicas with high

(>60%) levels of erucic acid would also be desirable for industrial purposes. Breeders have found it extremely difficult to achieve levels of erucic

acid higher than 55% of the total oil content. Because of the inability of

acyl transferases to insert erucoyl moieties in the 2-position of the triglyceride there may be a natural upper limit of 66% erucic acid obtainable in

Brussicu spp. (Taylor el ul., 1992).



11. IMPROVING YIELD



A. SEEDYIELD

1. Yield Components and Breeding Methods



Although improved nutritional quality of the oil and meal has been a

major breeding objective of Brussicu oilseed breeders, yield of seed, oil, and

protein must all be maintained and improved if these crops are to remain

competitive. Because seed yield is probably the most difficult and costly

trait to measure accurately, numerous attempts have been made to identify

the most important yield component(s). Positive relationships have fre-



AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS



11



quently been cited between the seed yield and the numbers of pods per

plant and per main raceme, as well as the numbers of seeds per pod and

seed weight per pod (Thompson, 1983; Shabana et al., 1990). In examining

yield and yield components of 10 European winter rape cultivars over a

3-year period, Grosse et al. (1992) concluded that high yields could be

attained from different combinations of three yield components- seeds

per pod, number of pods, and individual seed weight. However, as noted

by Thurling (1974b) and others, compensation among the various yield

components in response to environment occurs to such an extent in oilseed

brassicas that few breeders practice selection for one or even a few yield

components.

Observations on the contribution of various yield components to the

observed heterosis in hand-crossed hybrids have confirmed earlier findings.

Heterosis effects varied for each yield component depending on the environmental and/or genotypic effect when number of pods per plant, number of seeds per pod, single seed weight, and plant density were considered

(Lefort-Buson and Dattke, 1982; Schuster et al., 1985; Uon, 1989; Schuler

et al., 1992).

Given the importance of the oilseed brassicas, very few studies have been

undertaken to determine the physiological basis for increased yield. Thurling ( 1974a), who studied three Australian cultivars, found that correlations of total dry matter and yield were positive and highly significant

(r = 0.70). Allen and Morgan (1975) reported that leaf area index at first

flower was correlated to yield and concluded that a greater photosynthetic

source at flowering and after first flower would result in higher yield.

Campbell and Kondra (1978), studying single plants of three B. napus

cultivars, found that seed yield was significantly correlated with total dry

matter production (r = 0.2 1 to 0.52) per plant. Thurling (199 1) concluded

from a series of experiments with cultivars and breeding lines that early

flowering and maximum light penetration of the crop canopy are required

to maximize seed yield. The importance of light penetration of the crop

canopy is supported by the findings of Mendham et al. ( 1991). Comparing

the seed yield of an apetalous strain to a closely related petalous variety,

they attributed the higher yield of the apetalous strain to the 30% greater

solar radiation transmitted through the apetalous canopy. Although these

studies provide the breeder with some insight into the plant type that may

be highly productive, the measurement of such parameters is normally not

as efficient or effective in oilseed brassicas as the total measurement of

yield.

In conventional B. napus and B. juncea breeding programs for yield,

various forms of the pedigree system are employed [see Thompson (1983),

Downey and Rakow ( 1987),and Downey and Robbelen ( I989)]. However,



R. K. DOWNEY AND S. R. RIMMER



12



Table IV

Average Relative Yield of Winter Rape Parental Lines and Cultivars Compared to

Performanceof Syn-1 Synthetics and Seed Mixtures of P a r e d

seed yield as percentage of parents

Average of

parents



Syn- I

synthetic



seed

mixtures



Reference



100

100

100

100



I04

I14

I06

108



97

I05

106

104



Grabiec and Krzymanski ( 1 984)

Schuster and Friedt ( 1985)

E o n ( 1987)

Lkon and Diepenbock (1987)



'After Becker (1988).

the parameters of these systems differ from pedigree cereal programs in two

important respects. First, the oilseed brassica crops have a high multiplication rate per generation (- 1000: I), and second, the plant-to-plant outcrossing rate is much higher, ranging from 5 to 36% (see Section I,B,3).

Thus replicated progeny testing can begin as early as the F, and a certain

level of heterosis from the initial cross can be captured and retained in

subsequent generations. In a comparison of winter rape selection techniques, Sauermann (1989) found that in winter B. napus visual selection in

the F, for yield was superior to a random line selection, but the highest

yielding lines were identified by measuring yields of single-row F, progenies in a three-replicate test at one location or by testing sublines in the F4

with one replicate at each of three locations.

Because of the potential for significant levels of heterosis for yield in the

oilseed brassica species, the degree of natural interplant crossing, and the

absence of a highly efficient system of pollen control, synthetics have been

suggested as a means of capturing part of the available heterosis. Becker

( 1988) compared the performance of experimental synthetics of winter B.

napus to their parent lines or cultivars and noted that the synthetics yielded

some 4 to 14% more seed (Table IV). He postulated that even higher levels

of heterosis could be captured if the parents were selected on the basis of

their combining ability. On the other hand, in three of the four experiments, sowing mixed seed of the parents in the same drill run also resulted

in yield increases, which in some instances approached or equaled the yield

of the synthetics (Table IV). U o n (199 I ) found that cultivar mixtures and

Syn- 1s displayed greater yield stability than their corresponding F, hybrids

or any of the individual cultivars, suggesting that heterozygosity and het-



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Chapter 1. Agronomic Improvement In Oilseed Brassicas

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