Accelerated Approaches for Cabbage Improvement

Abstract

Cabbage is widely recognized as a good source of dietary fiber, minerals, vitamins C and provitamin A carotenoids and some glucosinolates that may have a chemoprotective impact in humans. It is a highly cross-pollinated crop where heterosis in F₁ hybrid progeny has been exploited for development of hybrids. The self-incompatibility and male sterility systems are present in the crop, which facilitates easy and cheaper hybrid production. Different conventional and biotechnological approaches are being utilized for the improvement of cabbage. Modern breeding approaches such as marker-assisted breeding and transgenic approaches such as Agrobacterium-mediated gene transfer and through genome editing techniques, which offer a new opportunity for genetic improvement of the cabbage. The molecular markers represent a useful resource for enhancing selection efficiency via marker-assisted selection (MAS) in cabbage breeding.

1. Introduction

Cabbage, scientifically known as Brassica oleracea L. var. capitata L., holds significant prominence as a cole crop cultivated worldwide. It possesses a diploid chromosome count of 2n = 2x = 18. Contemporary cabbage varieties have been derived from wild, non-heading Brassica (Brassica oleraceae L. var. capitata L.) through processes such as mutation, human selection, and adaptation. The origin of this phenomenon is commonly attributed to the East Mediterranean and Asia Minor regions. Various varieties of cabbage exist, distinguished by their respective characteristics such as shape, size, color, and leaf structure [1]. Cabbage is cultivated primarily for its leafy heads, which are frequently utilized in various culinary preparations such as salads, cole slaw, boiled vegetables, pickled dishes, and dehydrated products. Additionally, cabbage leaves can be fermented under pressure to produce sauerkraut. Cabbage is known to contain amino acids, minerals, ß-carotene, and ascorbic acid [2]. The substance in question exhibits a high concentration of proteins, minerals, and antioxidants, which have been found to possess anti-carcinogenic properties [3, 4] and anti-obesity properties [5]. Cabbage has been found to possess a protective effect against bowel cancer, which can be attributed to the presence of the compound indole-3-carbinol [6]. India is the second largest producer of cabbage globally, following China. The global cultivation of the crop spans across an expansive area of 2414 thousand hectares, yielding a substantial production of 70862.50 thousand tonnes. This equates to a productivity rate of 29.3 tonnes per hectare [7]. In the specific context of India, the crop is cultivated on a smaller scale, covering an area of 397 thousand hectares and resulting in a production of 9207 thousand tones [8].

2. Origin and evolution

The cultivated cabbages that exist today are derived from the wild cabbage species known as Brassica oleracea L., commonly referred to as colewort or field cabbage. The species in question is indigenous to the coastal regions of Western Europe and the Western Mediterranean. It thrives in challenging environments, specifically on ledges of chalky cliffs and even on near-vertical rocky surfaces where other plant species are unable to establish themselves [9]. The Chinese cabbage, turnip, rutabaga, and oil-seed rape have been derived from various Brassica species [10]. The cultivation of cabbage was documented in Germany by the year 1150, and there is evidence to suggest that it may have been introduced to England as early as the 14th century. The cultivation of this crop has been practiced in China since ancient times. The initial introduction of cabbage into the United States, specifically Virginia, can be attributed to the English colonizers [11]. The introduction of cabbage into Canada occurred in 1541 through the efforts of Jacques Cartier. The introduction of cabbage into India by the Portuguese predates the introduction of cauliflower by the British. However, its popularity only emerged during the period of British colonial rule [12].

The wild cabbage, a leafy winter annual that is found along the coasts of the North Sea, the English Channel, and the northern Mediterranean Sea, is considered the most probable candidate for an ancestral form. It is thought to have its origins in southern Europe and spread to other places by humans [13].

Based on current knowledge, it is indicated that contemporary cultivated crops have originated from the wild B. oleracea rather than the wild Mediterranean species, despite the likelihood of initial selection of various crop varieties taking place in the Mediterranean region [14]. The distribution of wild B. oleracea in the Mediterranean region appears to be improbable based on current evidence. The prevailing view suggests that early cultivated variations of B. oleracea were introduced from the Atlantic coast to the Mediterranean, where subsequent selection processes led to the development of various crop types. Nevertheless, it is important to acknowledge that the matter remains open to differing viewpoints. For instance, [15] all cole crops originated from the Mediterranean region, primarily through mutation and introgression from wild species during evolution or by human selection.

3. Cytogenetics

Cabbage and its botanical relatives exhibit a diploid chromosomal count, denoted as 2n = 2x = 18. Nevertheless, the examination of secondary chromosome associations could potentially imply that the value of x is either 5 or 6, thereby indicating that cabbage could be classified as a modified amphidiploids [16]. The cabbage plant possesses a somatic chromosome count of 2n = 18, with its genome being denoted as c [17]. The size of cabbage chromosomes is relatively diminutive. The classification of the genome of nine has been conducted based on its size. The chromosomal composition consists of one extremely elongated chromosome, four chromosomes of considerable length, three chromosomes of intermediate length, and one chromosome of relatively short length [18]. The composition of the c genome of B. oleracea was ABBCCDEEF [19]. Cabbage, classified as a subspecies of B. oleracea, is a secondary polyploid with a fundamental chromosome number of 6 [20]. Three of the fundamental chromosomes are present in duplication, and the other nine are single [21].

The most valuable genes for geneticists and plant breeders are those that can be easily recognized and inherited in simple mendelian ratio because such genes can serve as markers (Table 1).

Leaf color
A	Basic anthocyanin development factor series, intensifiers	[22]
Arc	Colored lamina; color intensifier in red cabbage	[22]
B	Light red midrib alone; with A gives a dark-red violet	[22]
S	Sun color	[23]
Leaf morphology and heading habit
gl	Glossy foliage	[24]
sm	Smooth leaves, with wr (originally S)	[25]
Pet	Petiolate leaves vs. sessile	[26]
W	Wide vs. narrower leaf	[26]
K	Dominant factor for heading	[27]
Plant habit T	Tall plant vs. short	[26]
Flower color and morphology
Wh	White petal, dominant, wh, yellow	[28]
cp	Crinkly petal	[29]
cr	Cream petal, recessive	[29]
Cytoplasmic male sterility
ms	Cytoplasmic factor with R, radish cytoplasm	[30]
Ms	Cytoplasmic factor with N, nigra cytoplasm	[28]
Self-incompatibility
S	Self-incompatibility, multiple alleles	[31]
Disease resistance
pb1, pb2	Duplicate genes, double recessive for resistance to P. brassicae race 6	[32]
F	Duplicate genes, double recessive for resistance to P. brassicae race 6	[33]
f	Major gene for resistance to black rot	[33]

Table 1.

Gene list of different characteristics of cabbage.

4. The breeding objectives pertaining to cabbage cultivation

• High, consistent crop production: Crop yield, the longstanding primary objective for breeders, remains a significant target, albeit with an increased emphasis on quality and additional parameters among most breeders.

• Quality: Crisp compact heads, a core length within half the head height, good flavor, and high nutrient content are all qualities a new variety should have.

• Disease resistance: Clubroot (Plasmodiophora brassicae), black rot (Xanthomonas campestris pv. campestris), fusarium yellows (Fusarium oxysporum f. conglutinans), downy mildew (Peronospora parasitica), turnip mosaic virus (TuMV), powdery mildew (Erysiphe polygoni D.C.), bottom rot (Rhizoctonia solani Kuhn) and tip burn are the most common diseases affecting cabbage, it is crucial to produce varieties that are resistant to many diseases.

• Resistance to early bolting: Cabbage is one of the most widely eaten vegetables at this time of year. Especially in years with a cold current in the spring, early bolting can result in significant economic losses for growers and breeders, highlighting the need for the breeding of early bolting resistant cultivars amenable to spring cultivation.

• Cold and heat tolerance: Cabbage must be bred for both cold and heat tolerance so that it may provide a high yield and mature quickly.

• Storage ability: The ability to store food for later consumption is a significant trait in cabbage, as is a compact head for ease of transport from the field to the market in the winter.

• Consistency: while sowing cabbage seeds at different times of the year, breeding early, mid, and late types completes the collection of cabbage variations, allowing for year-round harvesting.

• Uniformity of the crop: A consistent brassica field speeds up the grading process and cuts down on labor costs. The end goal is to have a field that is uniform in quality after being harvested just once.

• Appearance: The trait of color and shape holds significant importance in terms of appearance. The vegetable market has undergone a swift transformation due to advancements in packing and display facilities, resulting in a wide availability of commodities throughout the year. Additionally, the increased presence of visually appealing fruit and salad vegetables has compelled brassica producers to elevate their standards of presentation and quality.

5. Breeding methods

Due to the existence of sporophytic self-incompatibility, which results in heterozygous populations, cabbage is essentially a cross-pollinating plant that is mostly pollinated by bees and flies. Different population improvement schemes include mass selection, family breeding, recurrent selection, hybridization followed by selection in segregating generations, backcrossing, and heterosis breeding are breeding techniques that can be used to generate improved open pollinated types. In cabbage, selfing can be carried out for up to 3–4 generations without considerable inbreeding depression; however, the genotype affects the degree of inbreeding depression. Bud pollination is used for selfing one to two days before anthesis [34].

6. The systems for the development of hybrids

6.1 Male sterility

6.1.1 Genie male sterility

The occurrence of male sterility in B. oleracea is determined by a single gene, ms, which is a recessive trait resulting from a mutation of the male fertile gene, Ms. [9, 35]. Male sterile plants possess the ability to produce female fertile offspring, albeit with slightly smaller flowers and anthers compared to their male fertile counterparts.

6.1.2 Cytoplasmic male sterility

The presence of this characteristic was identified in Japanese radish [30]. CMS is caused by the interaction between nuclear and mitochondrial genomes. However, there is no fertility restorer gene present in any Japanese radish cultivar [36, 37]. Through numerous backcrosses, the cabbage nucleus was successfully inserted into the cytoplasm of the Ogura male sterile radish [38]. Regrettably, it was observed that all the genotypes of oleracea that were introduced into the cytoplasm of this radish displayed varying degrees of yellowing (chlorosis) in the young leaves when the seedlings were cultivated at temperatures of 12°C or lower [38]. The level of yellowing exhibited variation depending on the selection of recurring male parents. Two cytoplasmic male sterile cabbage germplasms through a breeding process involving the crossing of Raphanus (radish) and B. oleracea, followed by seven generations of repeated backcrossing with cabbage [39].

Nonetheless, both cabbage lines exhibited a slight manifestation of chlorosis, a condition that was resolved by means of protoplast fusion. In a study, a standardized protocol for the fusion of protoplasm in order to facilitate the transfer of desirable male sterility cytoplasm from broccoli to cabbage established [40]. Many male sterile lines created in a research using an improved cytoplasmic male sterile line known as R3625 that consistently displayed sterility while retaining normal growth and development [34]. presented A new cabbage hybrid, named Qiugan No.1, in their study [41]. This hybrid was developed by crossing the CMS line CMS02 with the inbred line 97,025-B. With consistent sterility, good adaptability, and great combining ability, 16 cabbage CMS lines [42]. The F1 hybrid Qiugan No. 4, a cabbage variety, was developed by [43] through the crossbreeding of the CMS line CMS95100 with the SI line 98,017-3-5-6-5-2. The compact head had a weight of 2 kilograms. The present study aimed to investigate the impact of Ogura cytoplasm introgression on various quality traits in a total of 17 cabbage lines belonging to the species Brassica oleracea var. capitata L. [44]. The transfer of Ogura cytoplasm was accomplished by introducing cytoplasmic male sterility (CMS) from the EC-173419 source line of cabbage obtained from the National Bureau of Plant Genetic Resources in New Delhi, India. This transfer was achieved by repeated backcrossing for a minimum of six generations, resulting in the incorporation of Ogura cytoplasm into various nuclear backgrounds of cabbage. The experimental findings demonstrated that the introduction of Ogura cytoplasm had a significant impact on various quality traits. Overall, there was an observed increase of 3–5 times in the concentration of various nutritional compounds in certain lines, whereas a reduction of 4–5 times was observed in others. The introgression of Diplotaxis catholica and Trachystoma ballii male sterile cytoplasms into cabbage background was carried out during the summer season of 2019. This was achieved through the utilization of backcrossing and embryo rescue technique [45].

6.2 Self-incompatibility

Given that cabbage sticky pollen is not dispersed by wind, it can be inferred that cabbage flowers rely on insect-mediated cross-pollination. The self-compatibility of plants varies depending on the cultivar, with some displaying self-incompatibility while others exhibit self-compatibility. Self-incompatibility serves as a mechanism to hinder self-fertilization, as well as the fertilization process in crosses involving plants with identical genotypes or nearly identical genotypes, wherein the expression of incompatibility specificity is identical due to dominance or co-dominance. The control of incompatibility specificity in brassicas is governed by a single locus known as the S gene [46, 47]. An elucidation of the self-incompatibility mechanism in B. oleracea, focusing on its cellular and molecular aspects provided [48].

According to the study conducted by [49], it was observed that Brassica oleracea typically exhibits a substantial number of S-locus alleles, often reaching up to 50. The initial cabbage hybridization occurred in Japan in 1950, employing self-incompatible lines. The hybrid was identified as Nagaoka No.1. Cabbage hybrids are currently generated through self-incompatibility mechanisms; however, a transition to male sterility is anticipated, likely to occur by the year 1997.

The degree of self-incompatibility can be evaluated by quantifying the quantity of seeds generated following either self-pollination or cross-pollination. The process of bud pollination as a mechanism to overcome self-incompatibility involves the deliberate opening of the bud and subsequent transfer of pollen from an open flower of the same plant [50]. The style and stigma of the flower become fully receptive approximately 3–4 days prior to its opening, during which time the self-incompatibility factor has not yet manifested. Consequently, self-fertilization becomes feasible, allowing for the circumvention of self-incompatibility [51, 52]. Currently, there exist two alternative approaches that have gained significant traction in addressing the issue of self-incompatibility [46]. The initial step entails the application of a sodium chloride solution with a concentration of 3–4% onto the exposed blossom. The flower is subsequently allowed to remain undisturbed for a duration of 20–30 minutes. Any surplus salt solution is eliminated by either blowing it off the flower or absorbing it with a moist cloth or paper towel. Following this, the process of self-pollination can take place. The application of salt facilitates the removal of the inhibitor present in the stigma, thereby enabling the process of self-pollination. An alternative and more effective approach, particularly when dealing with a large number of plants, entails the self-pollination of the exposed flowers, followed by the placement of the plants within an enclosed facility or chamber that allows for the controlled introduction of 5% carbon dioxide. Subsequently, the self-incompatibility mechanism is surmounted, thereby facilitating the generation of seeds subsequent to self-pollination [53, 54, 55].

7. Heterosis breeding

In order to successfully breed hybrid cultivars, three key prerequisites must be met. Firstly, a significant level of heterosis must be present. Secondly, a robust system for producing a large quantity of hybrid seeds must be in place. Lastly, an effective method for identifying hybrids with exceptional combining ability is essential [56, 57].

The phenomenon of heterosis in cabbage yield was initially observed by [28]. It was observed that there was a significant level of heterosis ranging from 30–100% in terms of yield in cabbage [58]. The hybrid combination of Enkhuizen and Valvatevka exhibited enhanced vigor, a more condensed growth habit, and increased productivity. According to [9, 59] findings, there was a notable presence of heterosis in relation to yield. In the diallel analysis conducted by [15], a total of six parents and 15 F1 hybrids were utilized. The findings of this study demonstrated the presence of heterosis, specifically favoring the superior parents in terms of the marketability of heads and net weight. A varietal cross between Copenhagen market and Pusa Drum Head demonstrated notable heterosis in relation to yield, net weight, and compactness [15].

The phenomenon of heterosis was investigated, revealing that hybrids exhibited increased plant weight accompanied by a relatively reduced number of outer leaves compared to their parental counterparts [60]. In evaluating the performance of 45 F1 hybrids for cabbage, [61] discovered considerable heterosis for head weight relative to superior parents in 22 hybrids. The heterosis for head bulk and homogeneity in single and double cross F1 hybrids in contrast to their double haploid inbred lines [62].

In order to create the F1 cabbage hybrid Zhonggan 192, [63] crossed the early maturing CMS- 87-534 (Cytoplasmic Male Sterile Line) with the inbred line 88-62-1-1. It takes 60 days from transplant to harvest. The cross combinations, namely SI I-4-6 × Glory-7, SI III-I-I × KGAT-1, IIS CMS × Glory-7, IIS CMS × KGAT-1, and SI III-I-I × E-1-1 & 2, exhibited notable positive heterosis compared to the control groups, indicating their high potential [64].

8. Resistance breeding

The development of resistant varieties is widely regarded as the most viable and environmentally sustainable approach for disease management. Resistance breeding has yielded numerous instances of success in diverse vegetable crops. However, the cultivation of resistant varieties necessitates a comprehensive comprehension of the evolutionary interplay between the host and the pathogen. The efficacy of resistance breeding hinges upon a comprehensive comprehension of the genetic origins of resistance, the racial composition of the pathogen, and the genetic underpinnings of the host-pathogen interaction. Understanding the scope of manipulation within the host-pathogen interaction is also crucial (Tables 2–4). The sources of R genes in plant breeding can include advanced breeding lines, newly developed genetic stocks through pre-breeding efforts, commercial varieties, landraces or primitive cultivars, and wild relatives in the form of original progenitors or related species. Additionally, one method of incorporating a resistance gene into a breeding program involves the incorporation of a resistant parent through hybridization. Moreover, the backcross technique is widely employed in breeding to introduce resistance traits into pre-existing adapted cultivars. This approach does not disrupt the overall genetic makeup of the recipient commercial variety. The transfer of monogenic dominant resistance to downy mildew and black rot into cultivated varieties can be achieved through the utilization of the backcross method. Moreover, the incorporation of a single R parent with favorable horticultural characteristics in the process of hybrid breeding can lead to the development of resistant hybrids against these specific pathogens. The gene pyramiding approach can be utilized to develop varieties that possess resistance to both the Kalia and Singh diseases [65, 66].

Diseases	Sources
Black Rot	MR-I, Invento (F1), 83-6, Pusa Mukta (Sel.8), AC 204, AC 208, RRM, RC-20
Alternaria	MR-I, AC 204, 83-6, 83-2, 83-1, RRM, 561, 563
Downy Mildew	MR-I, AC-204, 83-6, 83-2, AC-208, CC-10
Aphid (Brevicoryne brassicae)	All season, Red Drum Head, Sure Head, Express Mail

Table 2.

Sources identified In cabbage in India.

MR-I	Black Rot, Downy Mildew, Sclerotinia Rot, Alternaria, Diamond Back Moth
AC 204	Black Rot, Alternaria, Downy Mildew
RRM	Diamond Back Moth, Sclerotinia Rot, Black Rot

Table 3.

Multiple resistance sources identified in cabbage.

Disease	Pathogen
Bacterial
Black Rot	Xanthomonas campestris pv. campestris (Pammel) Dowson
Spot of Cabbage	Pseudomonas cichorii (Swingle) Staff
Club Root	Plasmodiophora brassicae War.
Fungal
Downy Mildew	Perenospora parasitica
Leaf Spot and Blight	Alternaria brassicae and A. brassiciola
Yellows or Fusarium Wilt	Fusarium oxysporum f. sp. conglutinans
Black Leg	Phoma lingum
Insect and Pest
Diamondback Moth	Plutella xylostella L.
Cabbage Stem Borer	Hellula undalis Fab.
Cabbage Caterpillar	Pieris brassicae L.
Cabbage Semi-loopers	Plusia orichalcea Fab. and P. nigrisigna Walker
Aphids	Brevicoryne brassicae L.

Table 4.

Important disease and insect Pest of cabbage.

9. Breeding for heat tolerance

Heat stress resistance refers to the differential performance exhibited by certain genotypes when exposed to equivalent levels of heat stress. The mechanisms associated with heat stress can be classified into two main categories: heat avoidance and heat tolerance. The ability of a genotype to dissipate radiation energy and prevent an increase in plant architecture to a stress level is indicated by heat avoidance. Six quantitative trait loci (QTLs) on chromosomes 2, 4, and 6 that are associated with resistance to head splitting. Two quantitative trait loci (QTLs), namely SPL-2-1 and SPL-4-1, are situated on chromosomes 2 and 4, correspondingly [67].

The markers BRPGM0676 and BRMS137 were found to exhibit a strong linkage with the trait of head-splitting resistance. Furthermore, these markers were observed to be conserved within the QTL SPL-2-1 region. During the months of October and November, an evaluation was conducted on two cabbage genotypes, PA-1 and PA-2, which are classified as ‘No-chill type’. The evaluation focused on determining the genotypes’ performance in terms of earliness and head yield. Among the tested varieties, PA-2 exhibited promising results in terms of head yield, achieving a yield of 22 metric tons per hectare. Additionally, PA-2 displayed desirable head traits suitable for November maturity [45].

10. Transgenics in cabbage

Genetic transformation includes two methods to transfer foreign genes into plants: Agrobacteriummediated gene transfer or the indirect method (vector mediated) and direct gene transfer (vectorless) method (Table 5). Through Agrobacterium tumefaciens-mediated transformation with Bacillus thuringiensis (Bt) cry genes, Jin et al. [70] targeted resistance to diamondback moth larvae in cabbage. All cabbage plants that were genetically modified with a synthetic Bt gene, specifically cry1Ab3, exhibited complete resistance to larvae of the pest. Agrobacterium-mediated transformation to introduce a synthetic fusion gene derived from Bacillus thuringiensis into a tropical cabbage breeding line known as ‘DTC 507’ [72]. This fusion gene encoded a translational fusion product consisting of Cry1B and Cry1Ab δ-endotoxins. In their study, Russell et al. [79] conducted a comprehensive review on the advancements made in the utilization of pyramided Bt genes cry1B and cry1C for managing populations of Plutella xylostella, Crocidolomia pavonana, Hellula undalis, and Pieris spp. in cabbage.

Cultivar	Technique of gene transfer	Gene transfer	Improvement in traits	References
King Cole	Agrobacterium tumefaciens	cry1a (c)	Resistance to diamond back moth	[68]
Yingchun, Jingfeng	A. tumefaciens	CpTI	Insect tolerance to Pieris rapae L.	[69]
Scorpio, Testie	A. tumefaciens	cry1Ia3	Resistance to diamond back moth	[70]
Uji	A. tumefaciens	GO	Enhanced tolerance to black rot	[71]
DTC 507	A. tumefaciens	cry1 b	Resistance to diamond back moth	[72]
Summer Summit, KY cross	Biolistic method	cry1Ab	Resistance to diamond back moth	[73]
A21-3	A. tumefaciens	cry1Ia8, cry1Ba3	Resistance to diamond back moth	[74]
Pride of India	A. tumefaciens	cry1Aa	Resistance to diamond back moth	[75]
Golden Acre	A. tumefaciens	betA	Enhanced salt tolerance	[76]
KY Cross	A. tumefaciens	AtHSP101	Increase the high temperature tolerance	[77]
AD BENTAM	A. tumefaciens	JMT	Resistance to heat stress	[78]

Table 5.

Transgenics for resistance.

11. Marker-assisted breeding

Marker-assisted selection (MAS) is a method in which the selection process is conducted based on a marker rather than the actual trait itself. The effective implementation of Marker-Assisted Selection (MAS) hinges upon the strong correlation between the marker and the primary gene or Quantitative Trait Locus (QTL) accountable for the specific trait [80]. The utilization of novel genomic tools expedites the process of identifying markers that are closely associated with specific genomic regions. The phenomenon of combining genetic material from various sources to confer resistance against a common disease is an illustrative instance and represents one of the most prevalent implementations of gene pyramiding. The utilization of molecular markers increases the probability of detecting the presence of a genotype that combines advantageous alleles within a population [81]. The utilization of contemporary molecular techniques has emerged as a significant factor in comprehending the arrangement and connections of the Brassica genomes. The findings from these studies not only validated the source of the amphidiploid species, but also indicated that the A and C genomes can be traced back to a common lineage, while the B genome is genetically distinct from both the A and C genomes, forming an independent lineage [82]. The genome of Cole, a member of the Brassica oleracea species [83]. This study also identified several molecular markers that are associated with significant traits in various Brassica oleracea crops. Genomic sequences serve as valuable resources in the creation of reliable DNA markers. The genetic maps in Brassica have a dual purpose: (a) to comprehend the interrelation between the genomes of the cultivated diploid species of Brassica, and (b) to facilitate the application of genetics and breeding techniques in the cultivation of various Brassica crops (Tables 6 and 7).

Trait	Gene	Marker	References
Genic male sterility	CDMs399–3	EST-SSR	[84]
Head shape	QTLs (Htd 3.1, Htd 8.1)	SSR, InDel	[67]
Head splitting	QTLs (SPL-2-1, SPL-4-1)	SSR	[67]
Yellow-green leaf	Ygl-1	InDel	[83]
Plant height, leaf length, head transverse diameter	QTLs Ph 3.1, Ll 3.2, Htd 3.2	InDel	[85]

Table 6.

Linked molecular markers in cabbage.

Source	Trait	Gene	Marker	Reference
DH line ‘Reiho P01’	Black rot-resistant	LG2 and LG9	CAPS and SRAP	[89]
Line ‘Early Fuji’	Black rot-resistant	C2, C4 and C5	SNP	[90]
C1234 inbred line	Black rot resistant	BRQTL-C3, BRQTL-C6	SNP-based CAPS	[91]
Glossy leaf cabbage (748)	DBM resistance	—	SSR	[92]
Brassica oleracea var. capitata; 96–100 inbred line	Head-splitting resistance	SPL-2-1, SPL-4-1	SSR and InDel	[93]
B. oleracea var. capitata; BN1 variety	High temperature and high humidity tolerant	—	SNPs	[94]

Table 7.

Molecular marker studies conducted for resistance to biotic and abiotic stresses.

12. CRISPR/Cas9 in cabbage

The utilization of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) has emerged as a contemporary technique for manipulating genomes [86]. The system comprises a nuclease known as Cas9, along with two short single-stranded RNAs, namely crRNA and tracrRNA. These two RNAs are combined to create a single-guide RNA (sgRNA), which is utilized for the purpose of genome editing. The Cas9 protein, in conjunction with a guide RNA (gRNA), combines to create a ribonucleo protein complex that subsequently attaches to the genomic DNA. The application of CRISPR-Cas9 technology for gene editing in Brassica vegetables. The study employed cabbage as the model plant and targeted the PsbS gene through the creation of a Brassica deletion mutant [86]. The utilization of preassembled ribonucleoprotein complexes (RNPs) in the introduction of these complexes into cabbage protoplasts using PEG 4000 as a facilitator [87]. Four single guide RNAs (sgRNAs) were utilized to target two specific endogenous genes, namely the FRI and PDS genes. Each gene was targeted by two sgRNAs. The introduced sgRNAs were subsequently assessed, and a mutation rate ranging from 1.15 to 24.51% was observed. In their study, [88] employed CRISPR/Cas9 gene editing to specifically target three genes in cabbage, namely phytoene desaturase gene (BoPDS), S-receptor kinase gene (BoSRK), and male-sterility-associated gene BoMS1. To facilitate this gene editing process, the researchers utilized a construct containing tandemly arrayed tRNA-sgRNA architecture. According to their findings, the mutation in the BoSRK3 gene resulted in the complete suppression of self-incompatibility, while the mutation in the BoMS1 gene led to the development of a fully male-sterile mutant.

13. Conclusions

Through the utilization of traditional breeding methods, substantial advancements have been made in the cultivation of numerous cabbage cultivars, which exhibit adaptability to diverse climatic and cultural environments. The task of producing cabbage with increased yield, improved quality, and enhanced nutritional value poses a significant challenge for plant breeders from the standpoint of consumer demand. The cultivars and breeding lines that exhibit resistance to black rot are distinct and should be perpetuated as valuable sources of novel germplasm for plant breeders. While the presence of glucosinolates in cruciferous crops remains a subject of concern, efforts will be made to develop cabbages not only for their culinary properties or adaptability to culture and management, but also for their therapeutic values. Contemporary methodologies, in conjunction with traditional breeding techniques, employ wild species and their relatives to effectively overcome diverse biotic and abiotic stresses in order to facilitate the creation of novel varieties. In forthcoming times, it will be imperative to prioritize the enhancement of nutritional characteristics, fortification against biotic and abiotic pressures, and the development of herbicide resistance using contemporary biotechnological methodologies. To date, limited endeavors have been directed towards enhancing cabbage through the utilization of advanced technologies such as transgenic methods and genome editing techniques like CRISPR/Cas9. These technologies are crucial for harnessing the potential of introducing genes that confer resistance to pests and diseases. Despite limited progress, it is imperative to address concerns regarding biosafety and environmental safety pertaining to transgenic crops. Furthermore, it is crucial to fully exploit the capabilities of contemporary biotechnological methods for enhancing the genetic traits of cabbage.