Perspective Chapter: Knowledge and Different Perceptions on Some Aspects in the Genus, Brassica

Abstract

Many years ago, the first Brassica species were propagated. There are several methods that can be used to grow Brassica plants, such as intergeneric hybridization, microscope cultivation, anther cultivation, CRISPR/Cas4 Technology and the phylogenetic analysis of Brassica genomes. The plants that have evolved from Brassica species are many, and these include Savoy cabbage, broccoli, mustard greens, Japanese mustard, horseradish, as well as kale. Although the main supplier of Brassica vegetables is China, these species have diverged and emerged to several other countries like Cyprus, Europe, Levant, Greece and the British Isles. Ogura cytoplasm introgression is a technique that has highlighted the differences in floral traits in species of Brassica plants. In cauliflower plants, pre-floral meristem division is a factor that’s often investigated, as divisions of this plant part demonstrates plant growth and mobility. This perspective chapter will address all aspects pertaining to the genus Brassica, and it will provide an account of key characteristics and functions ascribed to Brassica plants.

1. Introduction

It’s been many years since the first Brassica plants have been propagated. In successful attempts to grow these plants, it’s now apparent that there are many methods that can be used to grow them. This further implies that the Brassica genus of plants have become widespread, and this obvious statement is provided by fact that the plants of Brassica species are consumed everywhere, throughout the world [1]. In general, China is the main supplier of Brassica vegetables throughout the world, with approximately half of the produce being exported to other countries [2]. The genus, Brassica is made up of 37 different species, and of this, 6 are interrelated species, viz. Brassica nigra, B. oleracea and Brassica rapa, which are diploid, and 3 amphidiploids, viz. Brassica carinata, B. juncea and Brassica napus [3]. In terms of the common household vegetables, i.e. cabbage, cauliflower and broccoli, it has been reported by the Food and Agricultural Organisation in 2014, that the world’s total production of these vegetables is 105.7 million tons (cabbage), and 33.5 million tons (cauliflower and broccoli), respectively [2, 3]. The spicy flavour and pungent smell emitted from Brassica plants is ascribed due to the sulphur-containing compounds [4]. These compounds have many health benefits [2, 4].

2. Diversity and evolution

If one has to delve, or divulge, into the diversification and evolution of various Brassica species, it would be interesting to find that most of the world’s ‘cole’ vegetables - e.g. kale, cabbage, Brussel sprouts, kohlrabi, broccoli, collards, savoy cabbage and chinese kale, are derivates of the ancestral species, B. oleracea [5]. Therefore, the dispersion of Brassica plants over a period of time is said to be visualised through evolved characteristics, such as buds, inflorescence, leaves, roots and seeds [6]. The wild cabbage, or B. oleracea, is home to coastal cliffs of western Europe and the northern Meditteranean, and they have found a suitable habitat in the British Isles from Greece [5, 6]. Prior to the 15th century, i.e. in the early Middle Ages, not much was known about cauliflower plants, however, until recently, it has been documented that cauliflower plants probably were introduced into Europe from Cyprus or Levant [7]. In today’s world where a lot of molecular studies are being performed in plants, it has also been well emphasised that broccoli, an edible crop that’s widely sold, is the closest cultivated relative of cauliflower. This deduction is made with possiblities that the phenotype of cauliflower is more likely caused by a defective CAL gene, as tested and confirmed in a study performed on Arabidopsis [6, 8]. Therefore, the abnormal flowering, or flowers, of cauliflower are likely to have arisen from the floral stem primordia of cauliflower, and as a result of this mutant CAL gene [8], the flowers of cauliflower have lost their identity [5]. However, apart from this dissimilarity, cauliflowers and brocolli have a shared phenotype, since their qualities are much similar, for example, they both are short with reduced auxillary shoorts on multibranced flowering stems [5, 6]. The only difference is that the flowering stems of broccoli are much shorter, and that the buds that are produced are packaged densely [5, 6]. Furthermore, in cauliflower, although the primordia at the apex of each elongating shoot, the meristem, grow and develop into leaves, the later primordia fails to produce flower buds. It is, therefore, the meristem of the stem that continuously replicates itself in a spiral fashion, and the continuation of this up to the 10th order of branching, or more, causes the phenotype of cauliflower to be made of undifferentiated inflorescence meristems that are closely packed and clustered geometrically [5, 6, 8]. This texture of plants found in the family Brassicaceae is novel, and it’s absent in wildtype plants [9, 10].

3. Hybridization and embryo development

3.1 Techniques

Although, thus far, some species of plants from the genus Brassica have been reported, there are several other plants that belong to this diverse genus. Other Brassica plants include, among others, radish, arugula, watercress, horseradish, wasabi, daikon, gai-lohn, mustard greens, Japanese mustard and chinese broccoli [11, 12, 13]. We have now seen the manner in which the ancestral species of Brassicacaea spread to different regions of the world, and lead to so many methods of propagating these plants. Across the world, many attempts have been made to cultivate hybrids of Brassica oleracea var. botrytis, or the cauliflower. A particular reason for wanting to conserve this plant species is because of its health promoting properties [3, 12, 13, 14]. These properties are due to several chemicals present within them, such as anthocyanins, vitamins A, C, E and K, folic acid, phenolics, carotenoids, glucosinolates (as mentioned previously) [15] and selenium [16]. Currently, there are two main techiques used to generate introgression into Brassica crops [14]. In the first method, an inbred line that is double haploid is produced, since it is reported that homozygosity using both methods is pivotal. This statement is backed by findings that there are several problems associated with being able to identify and maintain S-allele homozygosity in cole plants, for example, in some instances, although an S-allele homozygote may be present, it may be weak, while in other cases, no zygote may be available, thereby questioning the reliability of these methods [15, 16]. However, nonetheless successes are reported with these methods, and successes are dependent on seed/microspore recalcitrance and bud size. B. oleracea var botrytis and B. napus are the most recalcitrant among the Brassica crops, and this seed behaviour is known to have a huge impact on embryogenic responses to culture conditions, such as media conditions and culture incubation conditions [17]. It has also been observed, in some situations, that although bud size has a considerable impact on microspore production in B. oleracea var botrytis, the nucleation of microspores has a considerable effect on the ability of the plants to complete embryogenesis. This means that seed/microspore viability is dependent on bud size, as reported in 2015 by Bhatia et al [18]. These authors have suggested that in order to obtain microspore of the highest viability, the buds produced need to be 4–4.5 mm in size [19]. However, this was deduced for plants that were in early and mid-maturation. In addition, they suggested that for cauliflower plants in the late maturation phase, the bud size should be between 4.5 and 5 mm for the microspore to have a high viability [14, 19]. However, although viability is required for embryogenesis, it is worthwhile to report that since microspores are totipotent, the ones that are binucleate may be antagonistic for embryogenesis in comparison to those that are uninucleate or in the early binucleate stages of development [20]. In cauliflowers with small flower bud size genotypes, it was found that a higher percentage of microspores developed, particularly when the microspores were in the mid to late uninucleated stage of development [20, 21]. This means that efficient seed embryogensis was ideal for microspores that were at the late uninucleate to early binucleate phases of growth. Using this method, about 50% of the plants produced were double haploids, and this was attributed to many exogenous and endogenous factors like culture and microspore density [17, 21, 22]. When the bud size was optimum for embryogenesis, about 60–65% of the microspore produced were reported as being viable. When the microspore density was >8 x 10⁴ per mL of culture, it was found that less embryos were produced. This could be due to nutrient depletion in the culture media, or competition for nutrients among the embryos [23]. Furthermore, toxic compounds present in the media may have had a drastic effect on some embryos, leading to death [24, 25, 26].

3.2 Sugar concentration vs. androgenic responses

Sugar concentration also has a huge impact on callus formation, and therefore embryonic development and androgenic responses. Just like with embryogenesis using seeds and/or microspores, in anther culture, media conditions also have a tremendous impact on embryo development, and thus, in this case, androgenic response (or androgenic capacity) [27, 28]. Roy et al. [27], reported that medium containing BS Salt with 100 mg / lt sucrose, 1 mg /lt 2, 4-D and 1 mg/lt NAA with 1 mg/lt BAP was sufficient to obtain successful androgenic callus development in tropical cauliflower. However, in general, it is recommended that a sucrose concentration of 140 g/l is sufficient to induce androgenic callus, with maltose and glucose being less effective in inducing callus formation. Yang et al. [17] highlighted that the genotype of a plant, as well as petal length, anther length and bud size has an influence on embryogenesis. Additionally, seasonally, the androgenic response among genotypes vary [28]. It was found that androgenic response to embryogenic growth was found to occur between 1 and 1.3 P/A lengths [14, 27, 28]. Further, Yang [29] also found that when the temperature was too high (25°C) or too low (e.g. below 10°C), the number of non-viable androgenic callus was high. This highlights the implications and necessity for having anther culture being performed during winter and spring seasons, rather than during autumn and summer season, because the latter seasons discourage the development of inbred lines, like in cauliflower and other crops [30].

3.3 Hybridisation and the case of the Japanese radish

Hybrid production in cauliflower is possible through a process called intergeneric hybridisation, or Ogura cytoplasm introgression [14]. This process involves a male, female and restorer line [1], with the restorer gene not necessarily required for hybrid seed production [31]. Inspite of this, this process is found effective to main homozyosity of the embryo, because submating has been found to disturb the uniformity of all 3 lines after 2 or 3 generations, and as a result a lower qualify hybrid is produced in comparison to the SI lineage zygote/curd [32]. However, during introgression, only the male floral traits appear to be reduced. Among others, these floral traits are flower size, length of style, and length of stamens. In contrast, the female traits remain intact, and include: petal colour, style shape, ovary type, and the presence of nectaries [1]. Since the curd, also referred to as the pre-floral meristem, is the edible part of the cauliflower, there is not a need to restore fertility, since the seeds are only used in propagatory practices [28]. Hence, the need for male sterility using genes from other crops belonging to the genus, Brassica. This procedure is necessary in order to prevent the formation of functional pollen grains, and in the process of doing so, keeping the female line functional and maintaining the female traits [33]. In R. sativa, or radish of Japanese origin, Ogura hybrid cytoplasm can be located [34]. This cytoplasm has been shown to be effective during intergenetic hybridization, particularly in plants that contain the Rf gene. An example of a radish cultiva possessing the rf gene is the European radish, in which Ogura introgression F1 hybrid breeding has been found to occur unlimited [35]. This unlimited hybridisation, due to the rf gene, has been found to produce rapid plant vigour, larger sized crops and nicely formed radishes. Similarly, in B. oleracea, cytoplasm male sterility is a method to prevent self-pollination so that the crops produced, like cauliflower, do not have reduced plant vigour, a small curd size, or deformed curd, as a result of suppressed inbreeding. However, despite the many advantages of male sterility cytoplasm, there are side-effects using this technique. This includes delayed chlorophyll development in the male sterile parts of B. oleracea var. botrytis, since introgression caused discoloration of the tissues, or chlorosis, since the Ogura hybrid cytoplasm from Japanese radish had chloroplast that was incompatible with the of B. oleraceae [36, 37]. In addition, there were also deformities found in the flowers, particularly as they were small in size, and it has been suggested that backcrossing may solve the problem. In order to solve the choroplast problem, it is suggested that interbreeding with protoplast between sterile male cytoplasm and an ordinary breeding line, may enable chloroplast compatibility. Moreover, there are also other problems associated with cytoplasm introgression, viz. unopened and partially opened flowers, rudimentary ovaries, low female fertility, poorly developed nectaries, and yellowing at temperatures below 15°C [38].

4. Genomes and leafing

The data from genetic studies and studies dealing with the phylogeny of B. oleracea are evidence enough that there is a relationship among cultivas and wildtype relatives belonging to the family, Brassicaceae. A study performed by Mabry et al. [39], suggests that Brassica incana shares its lineage with Brassica cretica and Brassica montana, and that these 3 species fall broadly under the B. oleracea species. The characteristics found in cauliflower plants, for example, are not entirely that of wildtype plant species, and, as previously described, much of the findings in B. oleracea are based on those found in cabbage crop varieties [40]. Therefore, given that the qualities exhibited in cauliflower plants are novel, and that experiments with Arabidopsis thaliana and B. oleracea show that there are similarities in both genomes [41], highlight that feral samples exist, and that these type of plants are not defined through cytoplasm introgression, hybridisation or culturing of the microspore or anthers of B. oleracea varieties. This also means that, in nature, one may encounter many domesticated crops that belong to Brassicacea, implying that species that belong to the genus, Brassica, may be that of a divergent population, another wild species, a wild conspecific, or even another domesticated species. Along the wildC genome, a newly identified wildC genome has been found [42], and this sequence is said to correlate to one cultivar and mixed wild ancestor of Tronchuda Kale [43] (when the wildC genome is compared to that of B. oleracea). However, in comparison to sample of B. incana, B. cretica, B. montana and B. oleracea, the wildC-2 gene wasn’t expressed. Instead, this gene was found to cluster in 6 other B. oleracea crop types, namely Brassica bourgeaui, Brassica hilarionis, Brassica insularis, Brassica macrocarpa, Brassica rapestris, Brassica villosa, and B. oleracea. In Chinese white kale, Bussel sprouts and curly kale, distinct clades that correspond to the growth habitat of these plants have been found. Since the clades are distinct, particularly because RNA collection is performed early in the development of these plants (i.e. approximately the 7th leaf stage), each one of them can be distinguished on the basis of their phylogeny [40, 44]. For example, Brussel sprouts are identified based on their oblong to circular leaves, while curly kale have leaf margins that are undulate or frill-like during early development [40]. Another factor to be considered is that season growth plays and important role in distinguishing characteristics among crops that belong to Brassicaceae. For instance, Chinese white kale is found to have lanceolate leaves, while those in curly kale are curly-like, as well as, the period for growth, i.e. Chinese white kale is an annual, instead of a biennial season plant [40, 45]. However, further genetic analysis of clustering, and distinct clades, among the 10 Brassica crop types have a substantial overlap in genes (17–98.3%) in both, B. oleracea and A. thaliana, and this means that some biological processes are overexpressed in B. oleracea, whereas others are reserved. For instance, the glaucous leaves of B.oleracea is because of modules of genes responsible for wax formation [46]. Some other processes are those producing herbivory defence compounds, via. Secondary metabolite biosynthetic processes, phenylpropanoid biosynthetic processes and metabolic processes, in addition to suberin biosynthetic processes (wound formation) [47].

5. Brassica origins: Feral or not

There has been much debate on the origin of Brassica plant species, particularly, because there is a bit of confusion about whether B. oleracea is a progenitor species or not [6]. Archaeological and environmental data suggest that B. cretica and B. hilarionis are sister species, that these two species are a likely progenitor species of B. oleracea [40]. This deduction is made with the knowledge that B. hilarionis is homozygous, and it is this trait that makes it ideal for domestication purposes through either gene editing or inbreeding practices [10, 48]. Although B. incana is found to be a wildtype crop, admixture inference data has suggested that some populations may be feral [49]. Similarly, B. cretica has also been found to be feral, however, some populations have been located as being domesticated. Using B. oleracea as a model for introgression, it is concluded that the genetic composition of particular cropts are a result of introgression from wild to feral populations. To add to problems associated with postdomestication of Brassica plants, it must be said that due to frequent introgression and difficulties in identifying seeds of individual crop types that it’s an extremely tedious task to obtain purely domesticated species of Brassica crops [48, 49]. It is, therefore, because of this gene flow between wild and cultivated populations that the evolutionary history of B. oleracea has become complicated. Just like B. incana and B. cretica, B. montana has also been identified as being partially feral in origin, however, there has been a dilemma regarding the relationship B. montana shares with B. oleracea [50]. Lanner et al. [50] has found, using chloroplast data, that B. montana and B. oleracea cluster together, whereas Panda et al. [51] went against this, and has suggested that B. montana is a subspecies of B. oleracea.

Although cabbage has its origins in the Meditteranean civilisations, B. cretica also has the same origins. This is said to have occurred due to germplasm transfer between wild and domesticated cultivats of Brassica crops [9]. However, today, B. cretica also occurs in Lebanon and it has been found to resemble B. cretica subsp. nivea, and it is this migration from Ionia, in the Western coast of present day Turkey ca. 2,102,050 BP, that suggests widespread trade of this crop by the early Mediterannean inhabitants [9]. However, it is because of he presence of Austrian archaeological evidence that we know that B. oleracea did not diversify itself from England [52]. Instead, because B. nigra and B. rapa are the major crops in Austria, and since there is evidence that B. oleracea existed in Greece during this period, we know that B. oleracea was absent in the Eastern Mediterannean, Europe, Britain and Czech Republic, due to the lack of data from these regions during this time [53]. Furthermore, there is no archaeological records on the cultivation of cabbages prior to the Late Iron Age (2350–2000) in Europe and the Roman periods (1950 1650 BP), however, there is documentation for the appearance of other Brassica species [54]. It is only around ca. 1850 BP that B. oleracea spread through seed dispersal to the Roman Empire [54]. Thereafter, many populations belonging to the Brassiciaceae family emerged in the British Isles [55], the Atlantic coast of Western Europe [56], South West England [57], and the Atlantic Coast of France [53]. However, in spite of this widespread dispersion of B. oleracea crops, these plants do not havehigh levels of genetic diversity, and some of them are isolated from other populations. Therefore, although they are wildtype plants, they are greatly feral in origin.

6. Genetic variation and introgression of the B. rapa genome

B. napus, B. juncea and B. carinata are associated with polyploidy, owing to the fact that resynthesis of diploid species hybridization, as well as, chromosome doubling influences the ability of the DNA to remain intact [58, 59]. As mentioned, it is due to the homozygous polyploid lines that make species in the genus, Brassica, ideal for scientific evaluation, specifically since self-pollination promotes the synthesis of DNA restriction fragments that vary, as well as phenotypes that differ among crops in Brassicacea [60]. Furthermore, inter-fertility is common among vegetables like cabbage, cauliflower, brocolli, brussel sprouts, and kohlrabi [61]. In a genetic study involving the genome of A. thaliana and Brassica species, it was a definite observation that some genes in Arabidopsis are related to Brassica quantitative trait loci (QTLs) [62]. In the Arabidopsis genome, chromosome 5 was found to be similar to a region in the chromosome of B. rapa, and this sequence is said to be a flowering-time gene, which was present as flc in Arabidopsis upon backcrossing. This finding, together with other sequences, viz. tfl1, flc, tfc2, co, fy, art1, emf1, efs, fha, gi, hy2, and vrn1, are all flower-associated gene, which participate in the genetic control of complete traits in the genus, Brassica. CAULI-FLOWER and APETALA1, are responsible for the curd-like inflorescence in Arabidopsis, however, the architecture of the curd produced, is far more complex, and, thus, it is under much complex genetic control mechanisms [8]. Therefore, the genome of Brassica is able to provide further clarity and insight about the size and shape of plants. In order to add to the concept of genetic variation, in 2022, Zhang et al. [63, 64], a study on introgression of the B. rapa genome into Brassica juncea was conducted. In this study, the researchers attempted to track segments of the B. rapa genome in the B. juncea germplasm. Currently, a lot of effort is being placed on conserving plant germplasm, particularly so that plants that are about to become extinct, or are at the verge of extinction, are able to be preserved and regrown, when the need arises. In Brassica, this is required because the seeds of all the crops belonging to this genus are unable to be separated based on morphological descriptions [8]. Therefore, by introgressing the B. rapa genome, it was observed that 59.2% of the A genome of B. juncea was covered by the donor segments. By using 132 single-nucleotide polymorphisms markers, it was suggested, that due to wide genetic diversity, that the recipient genotypes had a strong selection for the donor genetic sequence. The parental resequencing data in relation to the marker genotyping results show that there were morphological differences among the formation of leaf blades among the 3 categories of B. juncea parent plants [8]. In one case, the leafy head was maintained in the introgression lines, while in the remaining cases, the head was seen being more compact (due to the leaving heading around the shoot apexes and then folding upward and inward) and eventually, even, changing shape completely. This could have been due to the large gaps (>20 cm) in the 132 SNP marker, including gaps located on both ends of A01, A9 and A10 [8]. However, nevertheless, the expected results and that of which was obtained varied significantly in that the progeny retained the B. rapa genome in the process of distant hybridisation of the both studied species, i.e. B. juncea and B. rapa [8]. Therefore, the progeny existed in the heterozygous form, which is not ideal for selective breeding or gene transfer. Furthermore, the progeny inherited 57.31%, 59.57%, and 60.34% of the A genotype, and these percentages are that of heading, semi-heading and semi-heading II of the leaves of the progenies [63, 64, 65]. In terms of the lead regiments, the B. rapa and B. juncea parental lines showed no difference in retainment upon retrogression. This could have been due to certain regions in the B. juncea genome being not readily replaced by that of B. rapa segments.

Phylogenetic analysis of Brassica genomes with that of B. juncea introgression lines and representatives of B. juncea and B. rapa accessions, have revealed that the genetic diversity of B. juncea var multiceps (potherb mustard) and B. juncea var. megarrhize (root mustard) were much narrower that in comparison with heading mustard (which showed no diversification) [66, 67]. Furthermore, the dendrogram of 1642 SNPs of 154 investigated lines showed that the B. juncea introgression lines exhibited rich genetic diversity, and that the heading B. juncea accessions were measured independently of this genetic diversity. Studies found that the genetic distance of the heading B. juncea was increased to 0.33 from 0.03, and this relates to definite phenotypical variations among the introgression lines [63, 64]. Zhang et al. further, states that this introgression strategy could be extended to allotetraploid species of Brassica.

7. Biotransformation

7.1 The use of germplasm conservation and preservation

Aside from introgression, another technique used in the breeding of B. napus has to do with CRISP/Cas9 technology. This technology has been used in the creation of germplasm resources, as well as the genetic improvement of rapeseed [68]. In addition, many molecular mechanisms regarding this oil-bearing crop has been understood using this technology. Some of the methods involved with using this technology are the gene gun method, protoplast transformation method, pollen channel method, and, electric stimulation [69]. However, mutation detection methods have been found less effective than if it had to be applied to T. aestivum and O. sativa. Furthermore, gene knockout studies in B. napus are only possible if a specific promoter is able to be designed for CRISP/Cas9 system in B. napus [68]. This is probable, especially since both Arabidopsis and B. napus are related through their genomes, and since they belong to the same family - Cruciferae. With CRISP/Cas9 technology, B. napus genomes can now be targetted such that multiple DNA sequences can be edited, single clades (i.e. gene linkages can be avoided) obtained, and multiple mutations created through gene penetration [68]. This means that gene editing is advantageous in B. napus, since both the qualitative and quantitative traits can be analysed. In Gao et al. [70], the knocking out of BnaFAD2 and BnaFAE1, which controls the metabolism of oleic acid, was found to generate mutant materials with exogenous genes. If such can happen in B. napus using this technology, then, further products would be possible for this Brassica plant. In terms of progeny screening, by analysing gene editing materials, one is able to improve editing efficiency. This improvement can occur once mutations are detected in progenies and parent plants, and in which organ or propagule (type) the mutation has occurred in, because sometimes not all genetic mutations are transferred between generation. For example, in some cases, mutations may occur in the leaves and absent in the progenies of seeds, and vice versa [71]. Given that there are vast differences in the editing efficiencies between somatics and germ cells, it implies that the same technique/approach can be used in the transformation of B. napus, and that mutations can be eliminated by backcrossing and self-pollination of the B. napus species [68].

It has been found that the most important yield components of B. napus are: pods per plant, seeds per pod, seed weight, plant height and top branch angel [72]. Currently, CRISP/Cas9 technology is successful with removing gene resistance and creating multichamber pods. It is believed that this technology can help improve oil productivity in B. napus, but due to the complexity of this process, one may only be able to match pod length in relation to the shattering gene resistance, as independent factors [72]. In addition, studying BnaCLV3, CLV1, CLV2 and the signalling pathway (CLV pathway) responsible for producing different phenotypes, one could approximate - through experimentation - the type of chambered pods that B. napus could produce, i.e. dual chamber, multi-chambers, or single chambers. Furthermore, the seed weight of single B. napus plants of mutants could be deduced, as well as, the leaf numbers in relation to yield potential in B. napus [73]. BnaMAX1 genes are present in B. napus, which accounts for yield and petal character, while it is reported that apetalous plants are better suited to investigate photosynthetic capacity and disease resistance in B. napus [74]. Yang et al. (2018) described that the flowering times by regulating the growth genes, BnaSDG and BnaRGA, were more than 40 days sooner than in ordinary plants, and this was due to editing of their genes. These genes also participate in growth and chlorophyll synthesis of B. napus, and with editing of the BnaHemd gene, the photosynthetic rate, as well as the growth of B. napus may be studied [75]. In addition to this function, when BnaWRKKY11 and BnaWRKKY70 genes were expressed in Sclerotinia sclerotiorum (Lib.) de Bary, it was found that edited BnaWRKKT11 had no effect on different S. sclerotiorum in comparison to the wild type, whereas BnaWRKKY70 mutant exhibited as higher resistance to S. sclerotiorum, which Sun et al. [76] described as a negative regulatory factor in S. sclerotiorum. To add to this, it is known that the content of unsaturated fatty acids from B. napus can be increased by gene editing, however, the composition of fatty acids can also be changed with the editing genes [76]. Editing of the TT8 gene by CRISP/Cas9 technology, on the A09 and C09 chromosomes, produce a yellow seed phenotype. Futhermore, it was noted that the oil and protein contents of the mutant seeds were increased. This highlights that the seed coat-related genes in B. napus are responsible for oil content, seed coat thickness, and protein content, and that unlike black seeds, in yellow seed rape, the quality of the oil and protein produced are much better [72].

7.2 The use of structural variants vs. morphotype growth

The two B. oleracea morphotypes, namely cabbage and cauliflower, have been genetically studied using high-quality chromosome-scale genome assemblies. According to studies that use large structural variants, or SVs, the different morphotypes are a result of the different relations between the plants found in the genus, Brassica [77]. Furthermore, the intraspecific divergence, found to be exhibited by various variants of B. oleracea, are to be accounted for by the SVs. When 271 B. oleracea accessions were tested with these structural variants, it was found that various functions in cabbage and cauliflower were enhanced [78]. These functions are associated with plant responses to various cascades, as a result of stress factors, or stimuli. Also, flower development as well as development at the level of the premordia (as mentioned) - or meristem - were observed. As there is a lot of research performed on the development of curd in cauliflower, it is noted that this process can be mediated by many structural variants [78]. Studies have reinterated that there is a profound difference in vegetative and generative growth, and that both these processes are regulated by these structural variants. The switch from vegetative growth to generative growth is what drives inflorescence meristem proliferation, and this, in turn, results in curd development [79]. Therefore, the initiation, maintenance and enlargement of curd, is a result of SVs that have a considerable impact on development of curd, and it is those genes and SVs that form part of the regulatory network for curd development. The orange curd in cauliflower, for example, occurs as a result of a 4.7 kb insertion in the third exon of the Or gene, whereas, in rapeseed cultivars, an insertion of the 621 bp sequence in the promotor region of BnaFCCA10 is responsible for the adaptation of rapeseed plantations to winter climates [79]. With regard to comparative genomics, a study performed using full-length long terminal repeat retrotransposons (LTR-RTs)from Korso, Ox-heart and B. rapa revealed that centromeres were able to be identified on the genomes of cauliflower Korso and cabbage Ox-heart [77]. This as ascertained using fluorescent in situ hybridization analysis, and it was declared that there was genome and sub-genome divergence occuring in Brassica species, and this was achieved when synteny analysis was performed on Korso, Ox-heart, B. rapa and A. thaliana genomes and sub-genomes. Another remarkable finding was that some duplicated genes were retained during diploidisation, and this represented a biased retention pattern [80, 81, 82].

7.3 Genome sequencing and curd formation

The main purpose, or underlying basis, of performing genome resequencing is to be able to understand and investigate the dynamics of SVs (e.g. from Korso and Ox-heart) so that it’s possible to obtain morphologically different, or divergent, B. oleracea accessions. In Korso and Ox-heart, it is found that various biological processes are affected by at least one structural variant in the promoter region of genes [78]. These biological processes are: flower and meristem development, gene expression and epigenetic regulation, embryo development, cellular component organisation, response to stress and stimulus, signal transduction and cell differentiation [78]. In B. oleracea, the two indels, namely BoFLC3 and BoFRIu play two very differentiated roles. The first one helps broccoli to adapt to subtropical climates, while the second gene is involved in seasonal adaptation of cauliflower and cabbage - particularly the winter annual or biennial habit of these two Brassica species [83]. In addition to the above, B. oleracea contains homologues that assist in plants undergoing transition from the vegetative to the generative stages. For instance, BoFES1.1 and BoSUF4.2 have SVs in cauliflowers, and only when they are down-regulated that cauliflower plants adapt to the mentioned transitions. These homologues are, however, not found in cabbage [78, 83].

Although there are homologues that aid in the transition from vegetative to generative growth, there are others, such as PRC1 and PRC2, which assists in epigenetic modification, and thus assists in regulating the process of flowering. This means that it is because of the FLC-related autonomous and vernalisation pathways that a generative stage is reached at different timing intervals in cabbage and cauliflower. Introns and exons are particularly important during inflorescence meristem proliferation. An example where this is evident is in cabbage, where it has been found that Korso alleles are rare, whereas in cauliflower and broccoli, homozygous alleles for both structural variants are present [78]. This indicates exon deletions and intron insertion events in the Korso genotypes of all 3 crops, namely cabbage, broccoli and cauliflower. It is also worth noting that an upregulation of the BoWUS2 genes in all 3 crops result in both structural variants playing a vital role in curd formation [78]. In contrast, floral arrest and curd maintenance are processes that are essential for meristem development/arrest. In cabbage, it has been found that about 79.2% of accessions contained the OX-heart allele, while at the same locus point in broccoli and cabbage, the selection was for BoCAL Korso allele, and this suggested the role of this process in curd formation.

Some other genes that participate in the vegetative, transition and curd stages are the BoAP 1.2, BoFUL 1, BoFUL 3 and BoSEP 3, which are affected by structural variants [78]. There has been evidence that BoSVP 1 has an inverse relationship with curd development and flowering in that, in Arabidopsis, it was found that when this variant was upregulated for curd formation that its role in flower bud development suppression was more prominent, thereby highlighting its repressor role in the latter process. In addition, BoCCE participate in flower arrest, and it is found covering the entire genotype of Korso [84]. Through genotype experiments it has been found that it occurs in 97.1% pf cauliflower accessions, and that it is absent in cabbage and broccoli accession. This genetically emphasises that this gene arrests buds in the latter stages of development in broccoli, and much earlier in cauliflower buds [78].

There are several genes that participate in different phases of curd development. The below paragraph will mention a few, as well as their roles in this complex process. The first is the BoARL 2 gene that occurs to promote cauliflower curd size. The second is the BODRNL 1, which has a potential role in determining curd architecture, and which has deletions in its promoter region and determine curd development in cauliflower and broccoli. The helical growth is as a result of the BoTUA 2 and four BoTUA 3 genes found in Arabidopsis species [78]. During the initiation of curd, the transition from vegetative to generative growth is a result of the flowering-time regulation (FLC and FRI), while floral meristem arrest is a result of several matching floral genes, viz. CAL, API, SEP3 for organ size control, CYP78A5 and ARL are involved, which during curd spiral organisation, DRNL and TUA, are the genes that play and active role [78].

7.4 The TOC1 gene

In a study that attempted to unleash the genome of B. rapa, a study on finding duplicated orthologues in B.rapa was conducted [31]. This was done by analysing the TOC 1 genes found in the circadian rhythms pathways of A. thaliana. When this was conducted in order to assess non-coding conserved sequences, it was found that B. rapa retained copies of TOC 1 [85]. The authors questioned the relevance of this in the functionality of the genome of B. rapa, particularly, because they were concerns on the effect of this gene in circadian rhythmicity [85]. Their concerns had to deal with the cis-acting elements, as well as the promoter sequence participating in this process. This is because over a period of time, which fractionation, duplication was not possible, however, in B. rapa, the duplicate gene should not have existed since the gene families in B. rapa are not resistant to fractionation, and therefore it should not have been able to provide a signal to detect syntenic regions [86]. In addition, diploidization would have degraded the collinear signal. This degradation would have caused genes and genomic region transportation, chromosomal inversion, chromosomal fission and fusion, and, polyploidy events. This should have happened since Brassica is characterised by its paleohexaploidicity [86]. It is due to this that authors questioned whether there was something special about the truncation of intron 1 in Bra012964, and whether the interplay between this gene and TOC 1, are interrupting/stimulating the circadian pathway via sub- /neo-fractionisation of the homeologous genes involved in genome divergence in the family, Brassicaceae [31].

Thus far, you may have gathered that accessions relate to the utilisation of germplasm. However, much more needs to be done in order to make accessions more feasible. In the past, the 1950s, there were a variety of studies performed on cabbage germplasm. The studies performed are on ascorbic acid, dry matter, sugars, fibre, mineral elements, carotene, and proteins [87]. Furthermore, the accumulation and consumption of nutrients were also studied. Moreover, vitamins, pigments, and mustard oils in cabbage, turnips, and rutabaga and radishes were studied [87, 88]. Later on, by the 1970s, efforts were made to deepen studies on the diversity and biochemical composition of plants belonging to Brassica collections. And, in recent years, biologically active substances and biochemical components were being attempted to be studied for their health benefits. It is well known that in B. rapa, B. oleracea and R. sativus that accessions have been studied using SIRs, particularly since these plants have strong morphology and agronomy traits [89]. These traits are approximated to qualify and productivity, as well as biochemical traits, viz. dry matter content, proteins, sugars, ascorbic acid, chlorophyll and carotenoids [90]. The sections below would now focus on the health properties of plants of Brassica origin.

8. Biological effects on human health

Brassica plants have been found to possess many minerals and vitamins, and therefore, the crops from Brassicaceae have many benefits to human health. It has been found that the high folate content of the crops belonging to this species are able to reduce cancer, neural tube defects, as well as, vascular diseases [3]. The malignant and degenerative diseases, in contrast, are treated efficiently by the vitamin C, vitamin E and carotenoids found in these crops. In kale plants, for instance, a very high concentration of elements, namely: P, S, Cl, Ca, Fe, Sr. and K have been found [91, 92, 93]. While cabbage accumulates a considerable amount of copper, zinc and other trace elements, in broccoli, selenium is the main element that promotes health properties. Since Brassica can be grown hydroponically, independent of the other propagation methods, Cr, Fe, Mn, Se and Zn are elements that can, possibly, also, be extracted [15]. In contrast to cabbage, where trace elements can be found, in Radish, heavy metals are present, because this is a cruciferous species. Since the plants of Brassica are leafy, a fairly large amount of potassium are also found in them [11].

In addition to the above, Brassica also contains elements that account for pigmentation. For example, the anthocyanins are responsible for the red colour in red cabbage and broccoli species [15]. In terms of phenol compounds, the most common polyphenols occurring in Brassica species are flavonoids and hydroxcinnamic acid [15]. In Brussels cabbage, cabbage and broccoli, a fairly high concentration – say 1.500–2.000 ug/g – of glucosinolates are present. These compounds (β-thioglycoside-N-hydroxysulfates) are also prominent in horseradish, mustard, and the root and seed regions of Brassica vegetables [12]. In vegetable plants, approximately 75,000 μg/g of the fresh weight is what comprises the body of the mentioned plants. Although glucosinolates are hydrolysed in the human intestinal tract, in plant tissues they are biologically inactive [12]. Therefore, they are able to be utilised in cooked vegetables, more so, because the hydrolysed products are biologically active, whereas on the chemical and thermal front, they are stable. The glucosinolates have an essential role to plant in the treatment of cancers, particularly because the hydrolysis of these compounds in plant tissues are said to produce particularly useful products. During hydrolysis, in plant tissues, the enzyme β-thioglucosidase catalyse the breakage of the thioglucosidic bond, and this reaction causes the products; glucose and thiohydrosimate-o-sulphonate (or unstable aglycone) to be released [94]. Since glucosinolate produces products that are dependent on pH and the structure of glucsinolate ar the time of hydrolysis, there are a variety of products that are produced. Indoyl, ozazolidin-2-thiones, epithiitriles, thiocyanates, sulphides, isothiocyanates and nitrile are among the products produced. However, the compounds, glucosinolates, glucoraphanin, gluconasturtin and glucobrassicin, are anticarcinogenic, while, indol-3-carbinol have been found to inhibit breast and ovarian cancer. In addition to the anticarcinogenic compounds, isothiocyanates are phytochemicals present in some Brassica plants. Since they are a result of glucosinolate metabolism, it is expected that they have widespread functions [3, 95]. Some roles include their ability to reduce oxidate stress, alter cytokine activity (inflammatory response), induce apoptosis, inhibit angiogenesis, and inhibit cell cycle progession [96]. In addition, the isothiocyanates also possess anti-bacterial and anti-fungal properties, and this is related to its chemopreventative effect. There are 2 mechanisms involved in the chemopreventative properties of this phytochemical. The first one is that isothiocyanates inhibit cell cycle progression, initiating cell death, while the second involves the inactivation of phase I enzymes, and the activation of phase II enzymes [97]. The latter mechanism is responsible for stimulating the production of this phytochemical in Brassica vegetables.

The most natural phytochemical found in Brassica vegetables is called sulphoraphane. Another name of this substance is 1-isothiocyanate-(4R)-(methylsulfinyl) butane. This phytochemical is the most promising among the 4 chemopreventative agents found in Brassica crops. Just like isothiocyanate, sulphoraphane also inhibits tumour development by inducing cell-protective phase II enzymes [3]. Since vegetables of Brassica are consumed by humans, and mature broccoli is said to contain 10 times more sulphoraphane than juvenile broccoli cultivars, consumption of sulphoraphane is possible by humans [3]. It has been found that 10 mg of purified sulphoraphane can be tolerated by humans per day, while 100 mg of glucoaphanin is tolerable by humans per day. In order to prevent cancer development, it is recommended that humans consume 3–5 servings of cauliflower or broccoli per week [98].

9. Enzymes and biotransformation

It is because of the components found in Brassica crops that the enzymes involved in cancer prevention undergo biotransformation. These enzymes regulate the toxic, mutagenic and neoplastic effects of chemical messengers [99]. There are 2 type of enzymes, and these are the Phase I enzymes, and Phase II enzymes, which participate in DNA damage. The Phase I enzymes are the activators (cytochrome P-450, and Flavin-dependent monooxygenase), while the Phase II enzymes are the detoxifiers (GSTs, UDP-glucuronosyltransferase, sulfotransferase and N-acetyltransferase). These enzymes assist each other in the detoxification process. Phase I enzymes catalyse oxidation, reduction and hydrolytic reactions, and these reactions make compounds hydrophilic and accessible for detoxification. In contrast, the Phase II enzymes readily remove stable metabolites by catalysing conjugation, as well as other metabolic pathways that protect cell systems from electophiles and oxidants. Since the biotransformation of enzyme expression alters steroid hormone exposure, it is found that the progression of malignant and premalignant tissues are indirectly affected, and hence, carcinogenesis is affected [4, 12, 99].

There are many type of cancers that are affected by the substances present in Brassica plants. The paragraphs that follow would demonstrate this widely researched area.

In Brassica nigra seeds, sinigrin, a major product of glucosinolate hydrolysis, has been found to participate in liver tumour cell progression. It is said to achieve this through p53-dependent apoptosis. However, in rocket plant species, in a controlled experiment, apoptosis and necrosis was not induced by a p53-independent mode of cell death when glucoerucin was hydrolysed to 4-methylthiobutyl isothicyanate [100]. Instead, this compound was found to be selectively toxic to tumour-initiating cells. In another study it was found that cabbage and kale extracts caused DNA damage to be inhibited in rats, and this was said to be a result of the hepatocarcinogenic properties exhibited by cabbage extracts. This heptaoprotective effect is also present, and applicable, by the antioxidant properties of the volatile fatty acids found in cabbage plants [101, 102].

Unlike 4–methylthiobutyl isothiocyanate, 1-methoxy-3-indolylmethyl alcohol, another hydrolysis product of glucosinolate, forms DNA adjuncts in the liver, and this metabolite of neoglucobrassin, is a genotoxic carcinogen [94]. According to the World Cancer Research Fund, and the American Institute for Cancer Research, the risk of humans acquiring gastric cancer is inversely proportional to the high amount of Brassica crop intake. Since the level of 2-amino-1-methyl-6-phenylimidazole pyridine, and other dietary-related heterocyclic amine carcinogens, are increasingly eliminated through the consumption of Brassica vegetables, the risk of colorectal cancer appears to be reduced. This was found to be true when broccoli and Brussel sprouts consumed in the presence of well-cooked meat. This is a good finding, because, in the USA for example, colon cancer-related deaths are the third most common [103]. This statement if confirmed by 5 out of 8 controlled studies showing a reduction in cancer risk with high Brassica vegetable intake, with 3 studies showing a negative relationship. It is due to the reporting of negative relationship with Brassica vegetable consumption that it’s impossible for one to conclude that the consumption of Brassica crops are related to the risk of colorectal cancer development or inhibition [104].

Even through the affect of Brassica vegetable consumption on the risk of lung cancer is well-known, it’s impact is not as great as if one was to leave smoking. Lung cancer, in general, is caused by genetic lesions caused by exposure to smoking or ROS (reactive oxygen species), oestrogens, bacterial and viral infections [105]. Unlike colon cancer, lung cancer is the leading cause of death globally. When 1 μM of glucosinolate was isolated with cut rat liver slices for 24 hours, it was found that the glucosinolates were able to modulate the cytochrome P450 and Phase II enzymes, and this lead to the belief that glucosinolates have a profound effect on pulmonary carcinogen metabolism, and therefore, Brassica vegetables have the ability to exhibit chemopreventative activity in the lung of rats [106]. To date, no relationships between isothiocyanate urine levels and lung cancer risk in non-smokers have been reported. Also, the p53 status of lung cancer cells (A549; lung adenocarcinoma, H1299; larger lung carcinoma) have been reported as being affected in a dose-dependent manner upon isothiocyanate adenocarcinoma, and this was found through its cytotoxic effect. There is also evidence that the antioxidant effect of Brassica crops also play a role in protecting the cellular integrity and homeostasis of the benzo (a) pyrene [B (a) P]. This was found when 9 μmol/day of sulphoraphane were orally administered approximately 6 mice, and results on the basis of oxidative damage were noted. Unlike with lung cancer and smoking, breast cancer is age dependent, but not entirely [105]. In a study that consisted of 2832 women, aged between 50 and 74 years, when the deaths of 2650 women were compared, it was found that approximately 20–40% of the risk of breast cancer was induced [107]. This result was retrieved from women who consumed between 1 and 2 portions of Brassica vegetables. This result also assumed that the eating of these vegetables also altered the oestrogen metabolism pathway of these women. Furthermore, there was no relationship between cancer risk and the total vegetable and fruit consumption in the studied women. However, in a study that evaluated the effect of eating cauliflower on breast cancer, it was found that the substances contained in cauliflower had an inhibitory effect on breast cancer cells, in both oestrogen receptor-positive and oestrogen receptor-negative individuals [107]. In Chinese women, consuming Brassica crops reduced breast cancer when urinary isothiocyanate biomarkers were studied. In Caucasian women, on the other hand, the eating of broccoli was found to be negatively associated with breast cancer risk in premenopausal women, and this suggests that Brassica vegetables may be a curative agent in treating breast cancer in premenopausal women [108]. In men, on the other hand, prostate cancer is found to occur due to many reasons, but of those, the main issues arise due to nutritional status, particularly the consumption of fat and high fat foods [3]. The glutathionine S-transferase (GST)-∏ gene is said to play a role in the progression of prostate cancer, and this gene is said to disappear in prostate cancer, prostate cancer precursor lesions and prostate intra epithelial neoplasm. In a study where animals were fed with broccoli, it was found that the upregulation of this gene altered biotransformation enzyme levels in the peripheral tissues, thereby protecting against prostate cancer growth. In patients under 65, Brassica vegetables have been found to reduce the risk of prostate cancer, however, with the consumption of high amount of these vegetables, advanced and metastatic prostate cancer can also be managed [109].

Pancreatic cancer is also an illness that requires treatment using plants, particularly since in the USA it is the fourth cause of cancer-related deaths, whereas in Japan, it is the fifth. Cabbage has been shown to be most effective in treating pancreatic cancer among patients who consume 1 or more portions per week [110]. This observation was made with comparisons of subgroups of crops and fruits. Also, benzyl isothiocyanate, a member of the isothiocyanate family, was found to be an effective supplement alternative to X-ray therapy for pancreatic cancer. Bladder cancer, alternatively, occurs from the bladder epithelium, and is it this isothiocyanate present in Brassica vegetables that protect the epithelium cells from cancer. This was found in mice that were fed on broccoli sprouts. There, it was found that GST and quinone oxidoreductase in the bladder tissues and cells were induced, thereby preventing bladder carcinogensis [16]. Studies have reported that broccoli and cabbage, as well as other vegetables of the family, Brassicaceae, reduce the risk of bladder cancer. However, other type of vegetables and fruits may not necessarily be beneficial to reduce bladder cancer development. In a biological study, involving rats being fed on freeze-dried broccoli extracts, an alteration was found on the bladder, and bladder cancer was inhibited in a dose-dependent manner [111].

As already mentioned, many plants from the family, Brassicaceae, are involved in neurological diseases, and it had been noted that his has been due to oxidative stress. Furthermore, isothocyanates play an essential role in chronic diseases like cancer and neurodegenerative diseases [3]. This degradation product reduces the activation of cell death, and thereby also modulates inflammatory pathways, such as apoptosis. It does this by activating proinflammatory cytokine production, as well as, the production of oxidative species and the initiation of neuronal apoptosis death pathways, through NF-kβ translocation [112]. In a study where the Nrf2-ARE signalling pathways were activated, through mitochondrion function modulation, HSP70 gene transcription and expression, it was found that broccoli sprouts juice has a protective effect against β-amyloid peptide-induced cytotoxicity and apoptosis [113, 114]. In addition, due to Nrf2 activation, the broccoli juice was said to have also increased the activity of antioxidant enzymes, like HO-1, thioredoxin, thioredoxin reductase, NQ01, mRNA levels, as well as, intracellular glutathionine [112]. As a result of these roles of broccoli juice, it is said that plants of Brassica are effective to treat Alzheimer diseases [112].

There are various diabetic complications associated with diabetes. These complications include cardiomyopathy, nephropathy, neuropathy and retinopathy through Nrf2 activation [115, 116, 117]. Since Brassica crops form a part of functional foods, and sulphoraphane is an essential element of Brassica, type 2 diabetes mellitus can be controlled, instead of it reaching long-term complications. Since red cabbage has been found to decrease the catalase activity in diabetic kidney, it can be deduced that the functional foods belonging to this group are potential sources to treat diabetes [3]. Cholesterol is another factor which can be controlled by eating foods composed of Brassica vegetables. For example, broccoli sprouts has been found, over a course of a week eating 100 g fresh broccoli, to have decreased total, LDL and HDL cholesterol levels. Furthermore, this eating strategy has been found to improve cholesterol metabolism, and reduce oxidation stress markers [118]. In hepatoma-carry rats, on the other hand, cabbage extracts were found to decrease serum cholesterol levels. In addition, bile excretion and 7-alpha hydrolase activity in the faeces of these rats were increased. This suggested that cabbage determines cholesterol levels by increasing its metabolism in hepatoma developing rats. Also, in hypercholesterolemia patients, red cabbage and Brussels polyphenols affected the concentration of cholesterol in red blood cells membranes, and this is directly associated with the concentration of anthocyanins [119]. Thus far, it has been highlighted that the role of broccoli, and cauliflower, have profound effects on controlling neuro-degenerative diseases. However, in addition to the diseases mentioned, broccoli sprouts are also effective in the treatment of gastrointestinal diseases, via. Stomach adenocarcinoma, gastric ulcer, duodenal ulcer, chronic superficial gastritis, non-Hodgkins lymphoma, and gastric infection. Since Heliobacter pylori causes oxidative stress, a daily intake of 70 g/d glucoraphanin-rich broccoli sprouts for 2 months, they provide a protective role by presenting gastritis in humans and animals. Alternatively, sulphoraphane plays a cytoprotective role in the gastric mucosa by not inhibiting the severity of infections by Helicobacter pylori [120, 121].

The detoxification properties of Brassica vegetables contribute toward their anti-inflammatory properties by clearing free radicals and inducing immune functions. And, apart from the gastrointestinal disorders which Brassica vegetable can suppress, the compounds found in these plants can also be used to treat small incisions, wounds and mastitis. As it is known, glutathionine S-transferase (GST), plays a remarkable detoxification role in detoxifying carcinogens, environmental toxins and oxidative stress products. In addition, the vitamin c properties of Brassica plants have been found to be an effective antioxidant, which protects against various degenerative diseases [3, 104]. In a study that assayed the ascorbic acid content in B. oleracea, Singh [122] found that the cabbage (10 g) contained more ascorbic acid compared to cooked cabbage. This was ascertained using a large amount of 2,dichlorophenol indicator with raw cabbage, during the titration. It was concluded that there was a direct proportionality in the amount of 2,6-dichlorophenol used to obtain a pink colour [122]. The results showed that approximately 40–55 mg of ascorbate could be found in raw cabbage, and that this was in keeping with the recommended daily allowance (60 mg) that a person is ought to eat. The 15–29 mg ascorbate found in cooked cabbage highlights that the raw cabbage is a better source of antioxidants. Since cabbage contains ascorbate, it is recommended as a functional group, as it maintains healthy gums, teeth and bones, as well as participates in immunoprotection, like scurvy and rickets [122]. Brassica vegetables also promote an increase in the secretion of THS and thyroid cells as thiocyanate (metabolised from thioglycosides) inhibits iodine transport and the incorporation of iodine into thytoglobulin. The thiocyanate ions and oxazolidin-2-thiones are goitrogenic, because they contain a β-hydroxyl group. The goitrogenic activity can be counteracted by increasing the amount of iodine consumed in the diet. In a group of 293 Malaysian women, it was found that a high consumption of Brassicavegetables and mild iodine deficiency was enough to explain the high incidence of thyroid cancer against them. Therefore, a positive relation was established between cancer of the thyroid and the consumption of Brassica functional foods [3, 123].

10. Conclusion

The family, Brassicaceae encompasses many plant species that have many important biological properties, such as antioxidant, antibacterial and anticancer properties, among others. In this paper, various studies about the growth and propagation of Brassica plants have been discussed, particularly with reference to anther culture, microspore culture, and male sterility cytoplasm introgression. This paper also looked into the many features of Brassica plants, and perceptions, upon introgression of cytoplasm from on Brassica plant species to another. This was discussed quite intricately in relation to Brassica divergence, and the various traits such as the pattern of leaf growth in cauliflower and the origin of Brassica plants in general. It was reinterated, in this paper, that cauliflower and broccoli have many nutraceutical properties as functional foods, and that this stemmed from an original ancestor, the cabbage. In addition to the pattern of development in the inflorescence of cauliflower, introgression was also found to have an effect on the colouring of plants, and in cases it was occuringly prominent that chlorosis occurs during introgression. With regard to microspore culturing, an essential requirement was to maintain seed viability; so embryogenesis was possible. It was also undesirable to have self-pollination occur, as it is known to produce small curd size in cauliflower. A. thaliana was the ideal model for experiments with Brassica genomes. With Chinese white kale, for example, distinct clades were found as a result of biennial growth was favoured in this plant, over annualism. It was also established that more effort was required in germplasm experiments, and that germplasm was present for hybridization experiments, as well as experiments involving curd development. Furthermore, genome phylogenic analysis between heading mustard, B. rapa and B. juncea showed a narrow genetic diversity among each other. Also, CRISP/Cas9 technology may be successful in future to optimise oil production from B. napus. Furthermore, like with all plants, even in Brassica plants – like B. napus – the type of chambered pots produced are regulated by signal pathways, and gene coding may inhibit, or stimulate, the production of unsaturated fatty acids from B. napus. Structural variation have also been used to study meristem and flower development in cauliflower. In addition, in rapeseed cultivars, CVs are used to assess acclimatisation patterns to winter climates. Also, we have learnt about the different minerals and vitamins occurring in Brassica. A key component of glucosinolate hydrolysis, namely the sulphurphanes, is a key substance that inhibits turnover growth, and, as a result, it is a chemopreventative agent. This paper also detailed the various cancers which Brassica phytochemicals are able to treat, and in all cases these were either via the mitochondria, oe p-53-independent cell death. In addition, neurological defects, as well as, assaying of the vitamin C content of raw and cooked cabbage has also been discussed. In conclusion, this paper reports on the knowledge and different perceptions on some aspects in the genus, Brassica.