**2.2 Botany of radish**

Radish (*R. sativus* L.), an entomophilous flower, is an allogamous plant [35]. When it appears as three florets at the tip of each branch of the panicle during normal flowering, each flower is capable of producing a pod up to 1 to 3 inches long and holding one to six seeds [36]. The radish blossom's fresh corolla blooms in the morning and lasts till the following day [37]. The flower's pollen receptivity is present only for a brief duration each day, according to Kremer. Its clawed petals, four erected sepals, six stamens, and 1.5 to 2 cm broad, pink to purplish with purple veins, blooms in a 3 to 4 cm long style [38, 39]. A siliqua, sometimes called a seedpod, is a radish seed capsule that is 1.5 cm wide and 3 to 7 cm long. It bears a long, conical, and seedless beak and 6–12 seeds per pod [5]. The inflorescence of the radish is a typical Cruciferae raceme that is long, erect, and rectangular [40, 41]. Radchenko [42] studied the pollination of radish. When Crane and Mather [43] investigated how to cross-pollinate radish, they found that the "Icicle" and "Scarlet Globe" cvs were self-incompatible and pollinated by bees [44]. The research found that the number of honeybees visiting the radish

blooms significantly affected the quantity of seeds produced [37]. Honeybees pollinate radish blossoms at a rate of 77 to 99 percent on average, according to Radchenko [42], which increases crop yield by 22% and enhances seed quality. Consequently, it is thought that radish is almost entirely insect-pollinated [45]. While the fruit is developing, the color of the seeds is somewhat yellow, and they eventually become reddishbrown [46, 47]. The lyrate, pinnately distinct mature radish leaves feature a larger terminal lobe and smaller lateral lobes. They are arranged in a rosette condition, and alternate form [48]. Longer root types include winter radishes, daikon or mooli, and oriental radishes, which may grow up to 60 cm in length and with leaves as large as 45 cm by 60 cm in width [48].

#### **2.3 Characteristics traits**

It is a self-incompatible allogamous species. The considerable genetic variety of radish landraces and wild radish populations is paralleled in cultivar DNA polymorphism. Self-incompatibility may be overcome by bud pollination or highconcentration CO2 treatment, permitting the development of self-compatible progeny [49]. However, they exhibit inbreeding depression, making it difficult to get inbred lines. S-receptor kinase (SRK) is the recognition molecule of the stigma, similar to the self-incompatibility of Brassica species, whereas SP11, also known as SCR, is the recognition molecule of pollen [50]. These recognition molecule genes, SRK and SP11/SCR, have several alleles and are passed down through generations as the S haplotype. There are numerous S haplotypes in *R. sativus* [51], and the nucleotide sequences of some S haplotypes in *R. sativus* are similar to those of *Brassica rapa*, indicating that S haplotypes possessed by an ancient species were inherited by species in both *Raphanus* and *Brassica* without significant nucleotide sequence modification [50]. The majority of radish cultivars are root vegetables. The size, shape, and color of radish roots are all important. There has been evidence that quantitative trait loci (QTLs) influence root structure and color [52, 53]. Other factors, such as blossoming, influence root thickness. The QTL with the highest LOD score corresponded to a QTL for bolting time in our QTL analysis of root thickness using offspring obtained by crossing "Aokubi" with a white thick root and a rat's tail radish cultivar. This might be natural since early blossoming is thought to reduce root thickness. The transcriptome of developing roots was studied, and genes involved in root thickening were found. The color of the radish root surface is caused by anthocyanins. Pelargonidin and cyanidin are the pigments responsible for the red and purple colors of radish varieties. The finding of purple roots in a hybrid of a red root line and a white root line shows that the red and white had knockout mutations in separate genes involved in cyanidin synthesis and that the functional alleles in the red and white functioned as complementing genes. In red root cultivars, alleles of the flavonoid 3′-hydroxylase (*F3*′*H*) gene exhibit *Ty3/gypsy* transposon or helitron insertions [54]. A dihydroflavonol reductase (RsDFR) and anthocyanidin synthase (RsANS) gene are expressed in the epidermal tissues of red-skinned cultivar roots but not in white-skinned cultivar roots [55]. The huge seed size of radish is a distinguishing feature among Brassicaceae species. Radish seeds weigh nearly five times as much as *B. rapa* seeds. Because of the large seed size, the cotyledons and hypocotyls of seedlings are larger than those of Brassica. The bigger seedling size allows for direct sowing in the field and produces sprouts that are larger than Brassica. The form of siliques is connected with the property of large seeds. Amphidiploid plants of intergeneric hybrids of *R. sativus* and *B. rapa* have intermediate siliques with a few seeds in both the beak and valvar

#### *An Update on Radish Breeding Strategies: An Overview DOI: http://dx.doi.org/10.5772/intechopen.108725*

regions. Although the amphidiploid plants are mostly sterile, a small number of seeds may be obtained. Furthermore, the seed size is about midway between *Raphanus* and Brassica. Isothiocyanates, which are responsible for the pungent flavor of radish, are produced when glucosinolates are digested. The flavor of grated fresh radish and radish salad is significantly influenced by glucosinolates. The major glucosinolate in radish roots is glucoraphasatin (also known as 4-methylthio-3-butenyl glucosinolate, dehydroerucin), and the glucosinolate composition changes slightly. The glucoraphasatin content in Japanese radish cultivars, on the other hand, varies greatly [56]. There have been reports of QTLs impacting glucosinolate concentration in the root [57], and the genes inferred are putatively involved. Ishida et al. (2015) identified a mutant with a high quantity of glucoerucin but no glucoraphasatin, and the gene responsible for this mutation was discovered [56]. Although most radishes are salt tolerant, *R. sativus* var. *raphanistroides* is especially so [58]. Although genetic research into the salt tolerance of R. sativus var. raphanistroides has not yet developed, radish salt tolerance genes will be significant in the evolution of Brassica crops. High-temperature stress has become a major concern in radish growing. High-temperature stress causes the center of a radish root to become reddish brown, resulting in unmarketable products. However, since sensitivity to high temperature stress varies, it should be possible to develop a resistant cultivar. When radishes bolt, their roots become fibrous and unsuitable for sale. As a result, the characteristic of late bolting is favored. On the other hand, cultivars for oil production or rat's tail radish are needed to bloom even in tropical settings. Although vernalization is required for floral induction, rat's tail radish may bloom without it. Radishes, like many other winter crops, have varying vernalization needs. A QTL with a significant LOD score in a region containing an FLC gene was found using progeny from a hybrid between "Aokubi" and rat's tail radish. Although *Plasmodiophora brassicae's* clubroot poses a serious danger to crop yield, there are techniques to control it [58].

Among Brassica crops, Japanese and South Korean radish cultivars are often resistant to clubroot. Radish may be used to breed resistance in Brassica plants [59]. A quantitative trait locus (QTL) promoting clubroot resistance has been found on LG1 [60], which correlates with *Rs5* [61]. *Fusarium* yellow, caused by *Fusarium oxysporum*, is one of the most serious diseases in radish production. This disease causes wilting of the leaves and browning of the vascular tissue in the root. Certain cultivars and landraces have a high degree of resistance to *Fusarium yellow*. Because of its low ability for plant regeneration, radish is difficult to produce in tissue and cell cultures. There have been few reports of successful protoplast, anther, or isolated microspore culture [62], and protoplast, anther, and isolated microspore cultures are unusual [63, 64]. The function of isolated genes in radish cannot be shown due to the intricacy of plant transformation. The development of an efficient plant transformation technique is critical for scientific and practical radish research. Because plant regeneration capability must be genetically diverse, the first step in developing *in vitro* culture techniques would be to find cultivars or lines with high regeneration potential.
