**4. Plant ideotype for seed production**

For the first time in 1968, Donald introduced the concept of ideotype in plant breeding. Later in 1976, the concepts of isolation, competition and crop ideotypes were proposed by Donald and Hamblin [21].

#### **4.1 Ideotypes for solanaceous vegetables**

Manipulation of plant architecture of tomato may provide increased fruit yield resulting in increased seed yield. Suarma et al. [22] suggested emphasising on traits such as fruit yield (q/ha), plant height, average fruit weight for ideotype construction in tomato. Direct selection for these traits, having high heritability and genetic advance, may yield expected genetic up-gradation of a genotype. Sarlikioti et al. [23] suggested a new plant ideotype for optimization of light absorption and canopy photosynthesis in tomato. This new ideotype with more spacious canopy architecture due to long internodes and long and narrow leaves led to an increase in crop photosynthesis of up to 10%. Recently, Zsögön et al. [24] suggested that vital monogenic traits whose physiology has been revealed thoroughly can be molecularly tailored using genome editing techniques to achieve the target ideotype for elite cultivars of tomato. They also proposed that wild relatives or progenitors harbouring polygenic traits of interest could be de novo domesticated by manipulating monogenic yield-related characters through these techniques to get 'model type' plants which would perform expectedly in a defined environment. It has been suggested that shifting of crop plants from annuals to perennials may provide an additional advantage in seed yield. Eggplant ideotypes characterised by a radical change in plant architecture, with an arborescent or shrubby habit and perennial instead of annual fruit set using somatic hybridization [25–27].

#### **4.2 Ideotypes for cucurbits**

Plant architecture of muskmelon has also been manipulated to get increased fruit yield. Two different plant ideotypes have been proposed to get increase fruit set in muskmelon: "bush" or "birdnest" type possessing multilateral branches of the same length and bearing uniform sized fruits near the centre of plants and short internodes types having indeterminate growth behaviour and shorter internodes which can be planted at higher densities [28].

#### **4.3 Ideotypes for fabaceous vegetables**

Manipulation of the architecture of plants to achieve high seed production has been accomplished in various fabaceous species such as common bean, broad bean and pea; and also in the underexploited species of this family [29, 30].

Isaacs et al. [31] employed participatory plant breeding approach and together with farmers, identified specific traits that constitute a bean ideotype: adaptation, restricted height, columnar plant structure, even distribution of pods, fewer leaves, and earlier maturity. Plants with this ideotype produced good seed yield and were suitable for maize-bean cropping systems. Polania et al. [32] 2017 evaluated 36 bean genotypes to test the relationships between shoot traits and root traits under drought conditions. They identified two ideotypes related to efficient water use: water savers having a shallower root system and water spenders presenting more in-depth root system. Both showed greater root vigour under drought stress and produced high grain yield. Recently, Bodner et al. [33] identified ideotypes, having higher average yield, taller structure, more pods per node and longer flowering duration, suitable for Northern Europe. They considered Baltic landraces as promising ideotypes for increased *V. faba* yields in Nordic target environments as well as the other workers [34].

### **5. Seed set and development**

Since all vegetables are angiosperms, so a standard procedure of fertilisation, seed set and development is followed in all vegetables with few modifications. We are presenting here a general mechanism of fertilisation, seed set and development. At the time of fertilisation, protective coats, known as integuments and a central tissue called nucellus are present in the angiosperm ovule. If we see the structure of ovule, clear differentiation of these two integuments and nucellus can be found in the region of the micropyle, it is a minute pore in the integuments through which, the pollen tube enters the nucellus and move towards egg cell and polar nuclei. A stalk, funicle, attaches the ovule to the wall of the ovary. In general, megaspore mother cell inside the nucellus once divides meiotically and then divides mitotically three times to produce embryo sac or female gametophyte, a haploid eight-nucleate, seven-celled structure which comprises of one egg cell, two synergids, three antipodal and two polar nuclei. Although among angiosperms, the female gametophyte has a variety of forms, it may not necessarily encompass all these seven cells. On the other hand, inside the anther, microspore mother cell first divides meiotically and then mitotically to produce pollen grain or microgametophyte, which comprises two sperm cells enclosed with one vegetative cell [35].

These two female and male gametophytes play essential roles in the reproductive process of angiosperm. Sexual reproduction starts with the transmission of male gametophyte or pollen grain from anther to the carpel's stigma. Subsequently, pollen grain begins to germinate on stigma and a pollen tube carrying two sperm cells is formed, which penetrates the style. Growth and development of pollen tube is controlled by vegetative nucleus which disintegrates after serving its duty. Pollen tube enters into the embryo sac through micropyle, in general, and releases two male gametes. One male gamete fertilises the egg cell, called syngamy, and the second male gamete fuses with the central cell or polar nuclei [36]. Since two successive fertilisations take place, the procedure is known as double fertilisation. The zygote is formed after uniting of one sperm cell with egg cell, and this zygote gives rise to seed's embryo which is the starting of the sporophyte generation. Following

**61**

presented in **Figure 1**.

*Directing for Higher Seed Production in Vegetables DOI: http://dx.doi.org/10.5772/intechopen.90646*

**seed/fruit set and development**

families.

fertilisation, central cell's polar nuclei produce seed's endosperm, which is the nutrition source for developing embryo. These two embryos and endosperm encompass the central portion of the seed. Two synergids and three antipodal, remaining five nuclei, do not play any further role in seed development. For the development of viable seed, successful fertilisation of egg cell and the central cell is necessary [37]. All seeds mostly contain an embryo, a protective cover-seed coat and a reserve of food materials or any other specified tissue such as perisperm. Occasionally, polyembryony condition refers to development of more than one embryo in a single seed, may also be observed in some families such as Solanaceae and Amaryllidaceae

**6. Advances in the understanding of molecular mechanisms underlying** 

is becoming clear rapidly with the advancements of various omics studies such as genomics, transcriptomics and proteomics etc. and genetic transformation techniques. These mechanisms are generally conserved across all the angiosperms and may also be operated in vegetables. Various studies have been conducted in vegetables such as tomato (and cucumber to explore the underlying molecular mechanism of seed set and fruit set) [38]. In 2016, isolated and characterised two allelic mutants, twisted seed1-1 (tws1-1) and tws1-2 of a single copy gene (TWS1). This gene encodes a small protein of 81 amino acids which regulates embryonic

development and accumulation of storage compounds in the seed [39].

arresting of embryo development at the globular stage [41].

Underlying molecular mechanisms of seed set and development in angiosperms

This gene is specifically conserved among angiosperms and can be cloned from vegetables to explore its function in seed development in vegetables. The importance of AN3-MINI3 gene cascade in seed embryo development. Their regulatory model provided a deep insight into the seed mass regulation, which may be further explored to increase seed yields of vegetables [40]. Role of mitochondrial reactive oxygen species homeostasis in gametophyte and seed development has also been highlighted in angiosperms. It was reported that the effect of the mutation in *AtHEMN1* gene which encodes for coproporphyrinogen III oxidase. They showed adverse effects of *Athemn1* mutant alleles on gametophytic and seed development. Adverse effects included the development of nonviable pollen and embryo sacs with unfused polar nuclei, defects in endosperm development due to abnormal differentiation of the central cell and

To ensure successful sexual plant reproduction, fruit set or transformation of flowers to fruits is very critical. Role of hormones (i.e. auxin and gibberellins) in controlling fruit set after pollination and fertilisation have been well understood. It was shown that the role of microRNA-based (microRNA159/GAMYB1 and −2 pathway) regulation ovary development and fruit set in tomato. They initiated fruit set by modulating auxin and gibberellin responses using SlGAMYBs. On the other hand, proteins such as TIR1-like proteins have also been shown to have essential roles in auxin-mediated fruit development processes. Two TIR1-like genes have been identified in cucumber and designated as CsTIR1 and CsAFB2 [42]. Xu et al. [43] used tomato as a model plant to investigate the effects of these two genes on fruit/seed set. They highlighted the crucial role of the miR393/TIR1 component in fruit/seed set and concluded that post-transcriptional regulation of these two genes mediated by miR393 is vital for fruit set initiation in both cucumber and tomato. The different stages of seed development and the structure of a dicot seed is

#### *Directing for Higher Seed Production in Vegetables DOI: http://dx.doi.org/10.5772/intechopen.90646*

*Agronomy - Climate Change and Food Security*

**4.3 Ideotypes for fabaceous vegetables**

the other workers [34].

**5. Seed set and development**

two sperm cells enclosed with one vegetative cell [35].

Manipulation of the architecture of plants to achieve high seed production has been accomplished in various fabaceous species such as common bean, broad bean

Isaacs et al. [31] employed participatory plant breeding approach and together with farmers, identified specific traits that constitute a bean ideotype: adaptation, restricted height, columnar plant structure, even distribution of pods, fewer leaves, and earlier maturity. Plants with this ideotype produced good seed yield and were suitable for maize-bean cropping systems. Polania et al. [32] 2017 evaluated 36 bean genotypes to test the relationships between shoot traits and root traits under drought conditions. They identified two ideotypes related to efficient water use: water savers having a shallower root system and water spenders presenting more in-depth root system. Both showed greater root vigour under drought stress and produced high grain yield. Recently, Bodner et al. [33] identified ideotypes, having higher average yield, taller structure, more pods per node and longer flowering duration, suitable for Northern Europe. They considered Baltic landraces as promising ideotypes for increased *V. faba* yields in Nordic target environments as well as

Since all vegetables are angiosperms, so a standard procedure of fertilisation, seed set and development is followed in all vegetables with few modifications. We are presenting here a general mechanism of fertilisation, seed set and development. At the time of fertilisation, protective coats, known as integuments and a central tissue called nucellus are present in the angiosperm ovule. If we see the structure of ovule, clear differentiation of these two integuments and nucellus can be found in the region of the micropyle, it is a minute pore in the integuments through which, the pollen tube enters the nucellus and move towards egg cell and polar nuclei. A stalk, funicle, attaches the ovule to the wall of the ovary. In general, megaspore mother cell inside the nucellus once divides meiotically and then divides mitotically three times to produce embryo sac or female gametophyte, a haploid eight-nucleate, seven-celled structure which comprises of one egg cell, two synergids, three antipodal and two polar nuclei. Although among angiosperms, the female gametophyte has a variety of forms, it may not necessarily encompass all these seven cells. On the other hand, inside the anther, microspore mother cell first divides meiotically and then mitotically to produce pollen grain or microgametophyte, which comprises

These two female and male gametophytes play essential roles in the reproductive process of angiosperm. Sexual reproduction starts with the transmission of male gametophyte or pollen grain from anther to the carpel's stigma. Subsequently, pollen grain begins to germinate on stigma and a pollen tube carrying two sperm cells is formed, which penetrates the style. Growth and development of pollen tube is controlled by vegetative nucleus which disintegrates after serving its duty. Pollen tube enters into the embryo sac through micropyle, in general, and releases two male gametes. One male gamete fertilises the egg cell, called syngamy, and the second male gamete fuses with the central cell or polar nuclei [36]. Since two successive fertilisations take place, the procedure is known as double fertilisation. The zygote is formed after uniting of one sperm cell with egg cell, and this zygote gives rise to seed's embryo which is the starting of the sporophyte generation. Following

and pea; and also in the underexploited species of this family [29, 30].

**60**

fertilisation, central cell's polar nuclei produce seed's endosperm, which is the nutrition source for developing embryo. These two embryos and endosperm encompass the central portion of the seed. Two synergids and three antipodal, remaining five nuclei, do not play any further role in seed development. For the development of viable seed, successful fertilisation of egg cell and the central cell is necessary [37]. All seeds mostly contain an embryo, a protective cover-seed coat and a reserve of food materials or any other specified tissue such as perisperm. Occasionally, polyembryony condition refers to development of more than one embryo in a single seed, may also be observed in some families such as Solanaceae and Amaryllidaceae families.
