1. Introduction

Due to the scanty local production and yield, a large number of countries are to import Chilli from other countries. Improvement of high-yielding varieties is one of the main considerations to increase production. Quite possibly the main component for extending of production area is the prerequisite of high-yielding assortments. Consequently, several breeding projects have been carried out to increase the production of the crop ^[1][2][3][11,12,13]. To increase the current productivity of chilli as a vegetable crop less consideration has been paid to hereditary improvement. Utilizing the indigenous inferior quality cultivars with diminished resistance of open-pollinated genotypes against biotic stresses, are liable for low profitability ^[4][10]. To stay away from hereditary disintegration, it is essential to utilize existing genetic materials, the profitability chilli couldn’t be earned by utilizing open-pollinated varieties. Identification, and utilization, of appropriate parental lines, are fundamental for developing possible hybrids of chilli with high and stable yield. Moreover, improving yield, quality, and tolerance to cope with biotic and abiotic stress at the same time is a critical need of time ^[5][14].

In a hybrid development strategy, genetic diversity linked with combining ability is a criterion for selecting parents. At the point of crossing intersection among highly related parents then a low increase of heterosis is noticed, however high heterosis happens when the cross is made between parents of greater dissimilarity ^[3][13] and ^[1][11]. In the advance line selection process, heterotic group identification, pattern identification, and analysis of combining ability of sets of inbred lines play a significant role in chilli breeding ^[2][12] and ^[1][11]. At the same time, many studies have been conducted using heterosis breeding to increase chilli yield and quality traits ^[1][6][7][11,15,16].

Diallel research may be used successfully to learn about the combining ability of a set arrangement of self-and cross-pollinated populations. To distinguish appropriate parents for utilizing in crossing programs, including the assessment of the parents for a progression of crosses, and for estimation of heterosis in chilli, should be possible effectively through diallel technique ^[4][7][10,16]. Heterosis breeding employing the diallel technique can guarantee an improvement in chilli productivity due to the existence of integral quality activities and the occurrence of a high degree of non-additives quality effects ^[8][9][10][17,18,19]. Essentially, the system of peppers raiser is to accumulate in specific qualities a solitary cultivar with higher hereditary possible such as productivity, disease resistance, and bioactive compounds.

2. General Purposes and Classical Breeding Techniques Used for Capsicum Improvement

2.1. Common Goal for Capsicum Breeding

In chilli breeding, the breeders typically have major goals (Figure 14) with features such as production, disease, and pest resistance, fruit traits (bioactive chemicals, fruit color, pungent color, flavor), and abiotic stressors (salinity, drought, coldness, and heat) ^[11][21]. There are four main macro-objectives of chilli breeding and they are related to (a) key agronomies such as yield, color, and shape, plant habit and fruit; (b) the abiotic stress resistance, such as drought and salinity, limiting cultivation in certain regions, (c) bacterium-like, fungal and viral disease resistance, leading to severe damage to production and quality loss, and (d) quality which has a focus on the development of different bioactive substances such as capsaicinoids, isoprenoids, flavonoids, and vitamin C. for breeding goals ^[12][8].

Figure 14. The primary objectives of breeding initiatives for chilli peppers were adopted from ^[13][25].

All over the world breeders are continually trying to develop the hottest pepper that overcomes previously launched one. As a result, one of the major focuses in breeding agendas is to find the hottest chilli. Commercial breeders also use techniques to obtain hybrid increasingly hot for-profit and advertisement ^[14][24]. Currently, consumers are looking for ornamental peppers also in the market. Various European countries such as Germany, for example, have utilized these plants extensively to beautify landscapes and researching to better understand the physiology of this plant to improve aesthetic features ^[11][21]. Thus, the breeders are setting their goals to meet the market demands. There is a list of known characteristics that pepper raisers must possess.

2.2. Classical Breeding Techniques Used for Chilli Improvement

Chilli germplasm exhibits a wide range of variability. In accessions of gene banks, new sources of genetic diversity can be identified to obtain desirable genotypes. However, they must be correctly described to make their usage easy. Cultivars with high compound levels which play an important role in consumer health should be developed by breeders. ^[13][15][16][25,26,27]. Peppers (Capsicum spp.) are largely self-pollinated and diploid plants. Male and female regenerative parts are present in the Capsicum genotype as an ideal flower. They are inextricably linked to Solanaceae plants such as potato, tomato, eggplant, tobacco, and petunia. Despite the drastic change in genome size, all individuals in this family have a relatively large number of chromosomes in the genotype (2n = 2x = 24). There are some wild species that have chromosome number 2n = 2x = 26. The size of the C. annuum genome (3.48 Gb) at the assembled level is about three times more than that of the tomato. The typical exon/intron length is 286.5 bp/541.6 bp, genes are around 34,900 and translated portions are 2.34 Gb in total (76.4%). The hot pepper’s genome was divided into several syntenic blocks with the tomato genome, its next relative in the Solanaceae family ^[17][20].

The Capsicum’s description began in 1965 with 50 characteristics. Currently, there are 292 different characteristics, for example dw-1 (dominate plants 15 to 20 cm tall), Ef (early flowering), me-2 (Meloidogyne spp.), and others. Table 12 displays the fundamental methods used in the breeding of chilli peppers. The most often utilized cultivar improvement procedures ^{[15][18][19][20][21][22]}[26,28,29,30,31,32] include mass selection, pedigree (or genealogical) system, Single Seed Descent—SSD technique, backcross, selection of recurrent products, and hybridization’s ideal technique or a mix of strategies relies on how the features to be enhanced are inherited (monogenic, oligogenic or polygenic) ^[23][33]. The following is a brief description of the situation.

Table 12.

Major traditional approaches are employed in programs of

Capsicum breeding.

Name of the Approaches	Assumption	Reference
Mass selection	The next growing year stored seeds of the finest plants; the oldest technique	[24]
Pedigree method	Maintaining matings records and progenies. This comprises the selection and self-pollination of single plants.	[25]
SSD (Single seed descent)	This approach involves advances without selection of generations and is also used for the production of recombinant inbred lines.	[18]
Recurrent selection	Keep choosing individuals from a population and then crossing across to establish a new population.	[26]
Backcross	Especially for characteristics regulated by one or few genes involving the selection of individual plants and subsequent crossings for recurring parents	[19]
Hybridization	From one species genes or variations migrate via the crossover process	[24]

breeding.

2.2.1. Mass Selection

In ancient times the indigenous peoples of tropical America used Mass Selection effectively, collecting seeds from the best plants to be used in the following planting season. This technique can be utilized in circumstances when the traits are evident to identify populations with genetic variety and high heritage potential ^[22][32]. Conventional and Contemporary Approaches to Enhance Efficiency in Breeding Chilli/Hot Pepper ^[23][33]. This technique can also be used for the overall improvement of chilli especially for the genetic stock which will be used in breeding programs ^[27][28][34,35].

2.2.2. The Pedigree Method

The pedigree approach is followed by documentation of the cross and its offspring. This is carried out through the selection and self-pollination of individual plants. In the segregation and hybridization process, the superior variations are selected amongst superior plants together with the preservation of pedigree records ^[29][36]. The magnitude of heritable, and more particularly genetic components, is the most important aspect of the genetic constitution of the breeding material, which has a close bearing on its response to selection ^[30][37].

2.2.3. Single Seed Descent Method

In this approach, the selection is not carried out during the breeding process and recombinant inbred lines (RILs) are utilized in the development procedure. Advancement of generations can be performed in a controlled environment ^[18][28] to obtain lines resistant to various biotic stress. The biotechnological technique can be used in combination with conventional methods such as single seed descent (SSD), which allows homozygous lines and/or recombinant inbred lines to be obtained in a relatively short time ^[31][32][38,39].

2.2.4. Recurrent Selection

Individuals are selected from a distinct population, followed by crossings ^[33][23]. The original stock of seed is space-planting and superior seedlings chosen and separately harvested. As a result, each offspring of the plant is developed and progeny displaying higher output is bulk collected and subsequently tested in repeated testing with control cultivars. This procedure can help to select the recombinant more accurately compared to other methods ^[34][40].

2.2.5. Backcross

The traits which are controlled by one or a few genes can be improved by using the backcrossing technique, which involves selecting individual plants and successive crosses to a recurrent parent ^[35][19][5,29]. This has been an essential method for introgression genes from interspecific crosses. For fruit quality, disease resistance, or any other specific attribute a pure line can be improved by backcrossing to incorporate novel genes ^[20][30]. The gene-controlling resistance may contribute to the development of an improved chili variety and speed up the selection process, while also reducing genetic drag in the segregating population ^[34][36][40,41].

2.2.6. Hybridization

Hybridization is a key element in plant evolution because it provides novel genetic combinations. Single selection techniques can be used to improve most traits which are regulated both by additives and non-additives genes ^[22][32]. It may be possible to introduce an introgressive hybridization when one species’ genes transfer into another by an intersectoral hybrids process, and one parent passes successively. For example, in C. chinense PBC932 resistance has been passed on to C. annuum by traditional backcross ^[24][42] successfully at the AVRDC—World Vegetable Center—Taiwan. A new plant variety can be developed depending on the right approach. The Chilli flowers are structured in full, have calyx, corolla, sex organs for men and women. Through the manual emasculation method and subsequent pollination or utilizing the male sterility system ^[22][32], hybrid plants can be generated. Due to the difference between sex organs, the manual emasculation procedure is relatively straightforward. The technique consists of eliminating the male component and retaining the female structure (stigma). The breeder carries out crossings and puts the pollen from the plant that is used as the male parent in floral plant stigma used as mother ^[33][23]. A flower receiving pollen will be emasculated before this transaction to prevent contamination by the pollen itself. The crossing flora is covered with a label and prevents pollination by insects by contaminating foreign pollen.

2.2.7. Genetic Basis of Hybridization

Both intergeneric and interspecific are the two most prevalent sex types of hybridization. Interspecific hybridization happens where two species cross-fertilize, whereas intergeneric hybridization is produced with two species cross-fertilizing, which results in both parent phenotypes, genotypes, and development of the offspring ^[21][31]. Plant hybrids are created when the pollen from one kind of plant is used to pollinate an entirely different variety, resulting in a new plant altogether often known as first filial generation (F1) ^[22][32]. A typical hybridization method for Capsicum breeding is displayed in Figure 25 ^[23][33]. The difference in productivity between the hybrids and the mean of the parental genotype is characterized as the mid-parental heterosis. The better parent heterosis is defined ^[23][33] as a greater or better parental production. It is used to enhance vigor and produce more variability in cultivar growth. The chance of success in the production of hybrids is 15–25% greater than natural pollination. ^[28][35]. A hybridization to create improved segregants in the segregated hybrid community is necessary to find or locate the greatest feasible pairing of two or more ancestral genotypes to maximize variance in such a population ^[27][34]. Many breeding schemes were used for the assessment of general combining capacity (GCA) and specific combining capacity variations (SCA) for Solanaceae ^[21][31]. The GCA and SCA methods for quantitative genetic approaches for the determination of the characteristics and the ability to combine parental genes to generate the economically suitable plant attributes ^[29][36]. In describing hybrid development ^[27][34], the over-dominant concept of plant genetic might be employed. Over-dominantly, heterogeneous loci alloys exceed homogeneous parents, which refers to the use of the higher features in F1 in comparison to their predecessors. Heterosis or hybrid vigor is affected by a combination of genotypes, epigenetics, morphology, and ecology ^[23][33].

Figure 25. The technique of hybridization: In the previous evening before the flowers were opened, the desired flowers which were to be pollinated the next morning will be emasculated and covered with a plastic bag. On the following morning, the pollen of the targeted flowers was dusted on the female part and covered to avoid unwanted cross-pollination. Details about parents and pollination date have been put on a label. (Picture captured from author’s research field).

2.3. Using the Male Sterile Lines

Manual emasculation techniques are time-consuming and costly when hybrid seed production of peppers is commercially practiced. An alternative for solving this problem is to use male sterility. The Capsicum has been documented for both genital and cytoplasmic male infertility. In hybrid seed production, functional male sterility can be effectively used. Male sterility is therefore one of the main characteristics exploited in hybrid breeding ^[27][34]. The natural, spontaneous mutations or the effect of mutagenic agents might be shown as male sterile in peppers. For hereditary male sterility, more than 20 genes were identified genic male sterility (GMS). The use of male sterile lines as parents can therefore be an alternative to reducing costs. The experimental and commercial basis for hybrid seed business is widely utilized for men’s sterility, genicity, and cytoplasmic male sterility (CMS) sources ^[33][25][23,43].

The phenotypic selection of superior individuals from segregating populations is the major part of the conventional plant breeding approach. To breed a new/improved variety takes time, often between 8 and 12 years and even then, the release of improved variety is not guaranteed. The two principal limitations of the conventional approach are. The number of generations, and thus time. Therefore, to overcome the problem, it is wise to use modern approaches along with conventional ones.