Directing for Higher Seed Production in Vegetables

*Navjot Singh Brar, Dinesh Kumar Saini, Prashant Kaushik, Jyoti Chauhan and Navish Kumar Kamboj*

### **Abstract**

Vegetables are essential for human health and well-being. For sustaining an excellent production of vegetable crops, the seed is a primary input. Moreover, good quality seed is an important requirement for the vegetable industry, and there is a huge demand that has been expanding, considering the fact that seed multiplication is economically pertinent for vegetable cultivars to contend commercially. But the healthy seed production is usually a sumptuous trait and tormented by agricultural tactics, genetics as well as by the environmental factors. Features like seed output of the vegetables, sizeable genetic variation, the prerequisite for advancement and acceptance of a good quality vegetable seed. Here different mechanisms for seed production in vegetable crops has been presented, also vital areas and factors influencing seed production, and eventually discourses regarding the opportunity of plant breeding to sustainably make improvements to vegetable seed production.

**Keywords:** vegetables, self-incompatibility, male sterility, seed

### **1. Introduction**

Vegetables play a critical role in food security and are rich in mineral and vitamins. Vegetables can prevent several chronic diseases, including cancer [1]. But the successful production of vegetables depends on the first primary input that is the seed. Seeds are the consequences of sexual reproduction in the plant, and not all plants produce. Besides, the seeds are of tremendous organic and financial value. They have abundant protein, starch and oil reserves that assist during the early stages of development of a plant. These reserves are what make several portions of cereal and legumes main foods resources for any considerable proportion in the world's inhabitants [2]. Vegetable seeds signify a crucial organ intended for the multiplication of vegetables. Seeds accumulate well-balanced free of charge amino acids, which stored inside the seed storage proteins (SSPs). The seed quality is determined by the kind of amino acids, specifically crucial amino acids [3].

Vegetables require two successive processes, namely pollination and fertilisation, to produce the seeds. Pollination refers to the transfer of pollen from the androecium (male flower part) to the gynoecium (female flower part). Generally, flowers contain two other parts, the sepals and petals, which may be helpful to attract pollinators, namely insects. It is not necessary for flowers to have all of these four structures mentioned. Flowers either may be complete, having all four or incomplete, not having all four parts. Likewise, flowers may be grouped into perfect and imperfect

flowers [4]. There are two main types of pollination, namely, self and cross-pollination. Self-pollination refers to the deposition of pollen from the anther on the stigma located on the same plant (geitonogamy). It is the closest form of inbreeding which leads to homozygosity. Species having this type of pollination develop homozygous balance and do not exhibit significant inbreeding depression [5].

Whereas the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual is called cross-pollination. It is the form of outbreeding which leads to heterozygosity. Outbreeder species develop heterozygous balance and exhibit significant inbreeding depression on selfing. In addition to these two types of pollination, there is one a different kind of pollination, often called cross-pollination, where cross-pollination often exceeds 5% and may reach 30%. Various mechanisms such as bisexuality, homogamy, cleistogamy and position of anthers promote self-pollination, whereas other mechanisms such as dicliny (namely monoecy and dioecy), dichogamy, heterostyly, herkogamy, selfincompatibility (namely sporophytic and gametophytic) and male sterility promote cross-pollination [6].

Nearly one-third of the current global population is suffering from some form of malnutrition. Moreover, with a constant rise in the world population the food demand tends to increase up to 60% [7]. Vegetables being shorter duration crops can play a crucial role in providing more food per unit of cultivated area [8]. Similarly, climate change is a result of human activities primarily related to the emission of greenhouse gases. It means that there must be a focus on vegetable production and lowering the per capita emissions of greenhouse gases [9]. Vegetables are sensitive to temperature fluctuations, and environmental stresses have also been found to affect the nutrient composition of vegetables [10].

Monoecious, that is, cucurbits have both male and female flowers on different branches of the same plant. Dioecious (like spinach) have male (staminate) and female (pistillate) flowers on separate plants. Generally, both of these monoecious and dioecious plants require cross-pollination. Pollen grain germinates and penetrates the style to reach the ovary and then fertilises the ovule. This fertilised ovule changes into seed and the surrounding ovary develops into the fruit [11]. There are different agents for pollination such as insects, wind and water, etc. Insects are main agents for pollination in vegetables; they visit flowers to collect pollen and nectar as food and transfer this pollen unknowingly to the stigma of other flowers on the same plants or different plants. In this review, we have tried to comply with the important aspects for the successful and mass production of healthy vegetable seeds [12].

### **2. Pollination in vegetable crops**

Crops can be classified into three categories depending upon the mode of pollination, that is, naturally self-pollinated, naturally cross-pollinated and both self and cross-pollinated crops. Naturally self-pollinated: In such plants, same floral structure or different flowers on same plant houses both pollen and embryo sac. Examples are tomato (*Solanum lycopersicum* L.), lettuce (*Lactuca sativa* L.), parsnip (*Pastinaca sativa* L.), peas (*Pisum sativum* L.), dwarf bean (*Phaseolus vulgaris* L.) (**Table 1**).

Naturally cross-pollinated: in cross-pollinated plants, male and female flowers are present on different plants. While in some cases, the stigma may not be receptive at the time of pollen availability. For example, cabbage (*Brassica oleracea var. capitata* L.), cauliflower (*Brassica oleracea var. botrytis* L.), onion (*Allium cepa* L.), broccoli (*Brassica oleracea* var. *italic* L.), carrot (*Daucas carota* L.), radish (*Raphanus sativus* L.), pumpkin (*Cucurbita moschata* Duchesne), squash (*Cucurbita pepo* L.), beet (*Beta vulgaris* L.), muskmelon (*Cucumis melo* L.), cucumber (*Cucumis sativus* L.).

**57**

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

Carrot Brown anther and \*

*Commercial use of techniques in hybrid seed production.*

Onion \*

Pepper \*

Tomato and Brinjal \*

*Techniques of hybrid seed production.*

*\**

**Table 1.**

*Solanaceae*

*Cucurbitaceae*

*cucumerina*)

*pepo ovifera*)

*Cole crops*

botrytis)

*Fabaceae*

*var. gemmifera*)

Snake gourd (*Trichosanthes* 

yellow-flowered gourd (*Cucurbita* 

Brussels sprouts (*Brassica oleracea* 

Faba bean (*Vicia faba*) Partial cross

Cauliflower (*B. oleracea* var.

**Crops Techniques used for hybrid seed production**

Cole crops and radish Oguro type-cytoplasmic male sterility (CMS) and \*

Cucurbits Genetic male sterility mainly in muskmelon and \*

**Crop Pollination type Mechanism**

Bottle gourd (*Lagenaria siceraria*) Cross Monoecious Watermelon (*Citrullus lanatus*) Cross Monoecious Cucumber (*Cucumis sativa*) Cross Monoecious Gherkin (*C. anguria*) Cross Monoecious Muskmelon (*C. melo*) Cross Monoecious

zucchini (*C. pepo*) Cross Monoecious

Cabbage (*B. oleracea* var. capitata) Cross Sporophytic self-incompatibility

Kale (*B. oleracea* var. sabellica) Cross Sporophytic self-incompatibility Broccoli (*B. oleracea* var. italica) Cross Sporophytic self-incompatibility Turnip (*B. rapa* subsp. Rapa) Cross Sporophytic self-incompatibility

pollination

Common Bean (*Phaseolus vulgaris*) Self Self-fertilisation before opening the flowers

Potato (*S. tuberosum*) Self Bisexual, hypogynous Peppers (*Capsicum annuum*) Self Bisexual, hypogynous

incompatibility (SSI) with natural pollination

Hand emasculation and hand pollination

Tomato (*Solanum lycopersicum*) Self Bisexual, stigmas surrounded by anthers Eggplant (*S. melongena*) Self Bisexual, stigmas surrounded by anthers

Cross Monoecious

Cross Monoecious

Cross Sporophytic self-incompatibility

Cross Sporophytic self-incompatibility

(Cleistogamous)

Partly cleistogamous

pollination

S and T type-cytoplasmic male sterility (CMS) with natural pollination

(pinching and use PGR for staminate flower) or hand pollination

Genetic male sterility with hand pollination or natural pollination

petaloid sterility-cytoplasmic male sterility (CMS) with natural

Sporophytic self-

hand emasculation with natural

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


#### **Table 1.**

*Agronomy - Climate Change and Food Security*

cross-pollination [6].

flowers [4]. There are two main types of pollination, namely, self and cross-pollination. Self-pollination refers to the deposition of pollen from the anther on the stigma located on the same plant (geitonogamy). It is the closest form of inbreeding which leads to homozygosity. Species having this type of pollination develop homozygous

Whereas the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual is called cross-pollination. It is the form of outbreeding which leads to heterozygosity. Outbreeder species develop heterozygous balance and exhibit significant inbreeding depression on selfing. In addition to these two types of pollination, there is one a different kind of pollination, often called cross-pollination, where cross-pollination often exceeds 5% and may reach 30%. Various mechanisms such as bisexuality, homogamy, cleistogamy and position of anthers promote self-pollination, whereas other mechanisms such as dicliny (namely monoecy and dioecy), dichogamy, heterostyly, herkogamy, selfincompatibility (namely sporophytic and gametophytic) and male sterility promote

Nearly one-third of the current global population is suffering from some form of malnutrition. Moreover, with a constant rise in the world population the food demand tends to increase up to 60% [7]. Vegetables being shorter duration crops can play a crucial role in providing more food per unit of cultivated area [8]. Similarly, climate change is a result of human activities primarily related to the emission of greenhouse gases. It means that there must be a focus on vegetable production and lowering the per capita emissions of greenhouse gases [9]. Vegetables are sensitive to temperature fluctuations, and environmental stresses have also been

Monoecious, that is, cucurbits have both male and female flowers on different branches of the same plant. Dioecious (like spinach) have male (staminate) and female (pistillate) flowers on separate plants. Generally, both of these monoecious and dioecious plants require cross-pollination. Pollen grain germinates and penetrates the style to reach the ovary and then fertilises the ovule. This fertilised ovule changes into seed and the surrounding ovary develops into the fruit [11]. There are different agents for pollination such as insects, wind and water, etc. Insects are main agents for pollination in vegetables; they visit flowers to collect pollen and nectar as food and transfer this pollen unknowingly to the stigma of other flowers on the same plants or different plants. In this review, we have tried to comply with the important aspects for the successful and mass production of healthy vegetable seeds [12].

Crops can be classified into three categories depending upon the mode of pollination, that is, naturally self-pollinated, naturally cross-pollinated and both self and cross-pollinated crops. Naturally self-pollinated: In such plants, same floral structure or different flowers on same plant houses both pollen and embryo sac. Examples are tomato (*Solanum lycopersicum* L.), lettuce (*Lactuca sativa* L.), parsnip (*Pastinaca sativa* L.), peas (*Pisum sativum* L.), dwarf bean (*Phaseolus vulgaris* L.) (**Table 1**). Naturally cross-pollinated: in cross-pollinated plants, male and female flowers are present on different plants. While in some cases, the stigma may not be receptive at the time of pollen availability. For example, cabbage (*Brassica oleracea var. capitata* L.), cauliflower (*Brassica oleracea var. botrytis* L.), onion (*Allium cepa* L.), broccoli (*Brassica oleracea* var. *italic* L.), carrot (*Daucas carota* L.), radish (*Raphanus sativus* L.), pumpkin (*Cucurbita moschata* Duchesne), squash (*Cucurbita pepo* L.), beet (*Beta vulgaris* L.), muskmelon (*Cucumis melo* L.), cucumber (*Cucumis sativus* L.).

balance and do not exhibit significant inbreeding depression [5].

found to affect the nutrient composition of vegetables [10].

**2. Pollination in vegetable crops**

**56**

*Techniques of hybrid seed production.*



#### **Table 2.**

*Different kind of pollination mechanisms in the vegetable crops.*

Other cucurbits (bitter gourd, bottle gourd, ridge gourd, sponge gourd, snake gourd, pointedgourd, ash gourd, etc.), amaranths.

Both self and cross-pollinated: Plants are primarily self-pollinated, but crosspollination occurs to varying extents. Examples include brinjal (*Solanum melongena* L.), okra (*Abelmoschus esculentus* (L.) Moench), chilli (*Capsicum annuum* L.), sweet pepper (*Capsicum* spp.). After landing on stigma, pollen grains germinate and grow down the style of the flower, and this process is called fertilisation. Sperms of the pollen unite with ovules in the ovary which leads to seed production. In the event of pollen incompatibility, a fully pollinated flower does not get fertilised. Some plants are capable of producing fruit without fertilisation and seed production, and such species are called parthenocarpic [13, 14].

Among the different pollination agents like wind, birds, insects, gravity, water and mammals, the most important are insects. Insects contribute 80–85% of the pollination, out of which a hefty proportion of 75–80% is attributable to honey bees. Because of their body characteristics and behaviour patterns, solitary bees, bumblebees and honey bees constitute the largest group of pollinators. Pollination by insects is indispensable for improvement of plant and yield characteristics like seed set, quality of produce, early flowering, oil content, rubber content, pyrethrin content, etc. Managed pollination of crops by honey bees is a surest and most effective way of increasing yield and quality of the produce. Honey bees enhance productivity of crops through cross-pollination along with additional income through production of honey and beeswax, etc. Honey bees and other cross-pollinating agencies like bats, small mammals, birds, etc. owing to its body modifications to pick pollen, floral fidelity, efficiently communication among the colony members and their adaptability to different climates [15]. Cross-pollination results in hybrid vigour, thus improving the quality as well as quantity of the produce which is a boon for vegetable seed production (**Table 2**).

### **3. Effects of insect pollination on seed yield of vegetables**

Inadequate pollination has been a major constraint to the potential returns of vegetables. Different insect pollinators have been identified in various vegetable crops, which increased the seed yield by increasing the pollination. Vinícius-Silva et al. [16] found fifteen floral visitors with *Exomalopsis analis* being the most

**59**

hybridization [25–27].

**4.2 Ideotypes for cucurbits**

which can be planted at higher densities [28].

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

additional input in enhancing the yield [18].

central curd cutting employed together.

**4. Plant ideotype for seed production**

were proposed by Donald and Hamblin [21].

**4.1 Ideotypes for solanaceous vegetables**

representative in tomato crop. They also reported the presence of the other two effective pollinators, namely *Apis mellifera* and *Trigona spinipes* in tomato crop. Shah et al. [17] observed the highest population of honey bees among all tracked pollinators in cucumber and showed that insect pollination in cucumber acts as

Similarly, the highest weight of fruits, number of seeds per fruit, fruit size and TGW was achieved in honey bee pollination compared to others. Azmi et al. [19] observed heavier, longer and larger fruits in cucumber when pollinated by stingless bee (*Heterotrigona itama*) and hand compared to those produced from pollination without *H. itama*. Rouf et al. [20] reported an increase of 45.46 and 23.17% in seed yield of cauliflower plants pollinated by honey bee over plants grown inside net without bees and open pollination, respectively. Further, they showed that maximum yield attributes of seed could be achieved if planned bee pollination and

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

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

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

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

*Agronomy - Climate Change and Food Security*

Fenugreek (*Trigonella foenum-graecum*)

**Table 2.**

**Crop Pollination type Mechanism**

Lima bean (*P. lunatus*) Self Cleistogamous flower structure

Cowpea (*Vigna unguiculata*) Self Cleistogamous flower structure

Chickpea (*Cicer arietinum* L.) Self Cleistogamous flower structure and stigmas

sweet pea (*Lathyrus odoratus*) Self Cleistogamous flower structure and stigmas

Pea (*Pisum sativum*) Self Cleistogamous flower structure and stigmas

Soybean (*Glycine max*) Self Cleistogamous flower structure and stigmas

surrounded by anthers

surrounded by anthers

surrounded by anthers

surrounded by anthers

Self Cleistogamous flower structure

pointedgourd, ash gourd, etc.), amaranths.

*Different kind of pollination mechanisms in the vegetable crops.*

species are called parthenocarpic [13, 14].

boon for vegetable seed production (**Table 2**).

**3. Effects of insect pollination on seed yield of vegetables**

Inadequate pollination has been a major constraint to the potential returns of vegetables. Different insect pollinators have been identified in various vegetable crops, which increased the seed yield by increasing the pollination. Vinícius-Silva et al. [16] found fifteen floral visitors with *Exomalopsis analis* being the most

Other cucurbits (bitter gourd, bottle gourd, ridge gourd, sponge gourd, snake gourd,

Both self and cross-pollinated: Plants are primarily self-pollinated, but crosspollination occurs to varying extents. Examples include brinjal (*Solanum melongena* L.), okra (*Abelmoschus esculentus* (L.) Moench), chilli (*Capsicum annuum* L.), sweet pepper (*Capsicum* spp.). After landing on stigma, pollen grains germinate and grow down the style of the flower, and this process is called fertilisation. Sperms of the pollen unite with ovules in the ovary which leads to seed production. In the event of pollen incompatibility, a fully pollinated flower does not get fertilised. Some plants are capable of producing fruit without fertilisation and seed production, and such

Among the different pollination agents like wind, birds, insects, gravity, water and mammals, the most important are insects. Insects contribute 80–85% of the pollination, out of which a hefty proportion of 75–80% is attributable to honey bees. Because of their body characteristics and behaviour patterns, solitary bees, bumblebees and honey bees constitute the largest group of pollinators. Pollination by insects is indispensable for improvement of plant and yield characteristics like seed set, quality of produce, early flowering, oil content, rubber content, pyrethrin content, etc. Managed pollination of crops by honey bees is a surest and most effective way of increasing yield and quality of the produce. Honey bees enhance productivity of crops through cross-pollination along with additional income through production of honey and beeswax, etc. Honey bees and other cross-pollinating agencies like bats, small mammals, birds, etc. owing to its body modifications to pick pollen, floral fidelity, efficiently communication among the colony members and their adaptability to different climates [15]. Cross-pollination results in hybrid vigour, thus improving the quality as well as quantity of the produce which is a

**58**

representative in tomato crop. They also reported the presence of the other two effective pollinators, namely *Apis mellifera* and *Trigona spinipes* in tomato crop. Shah et al. [17] observed the highest population of honey bees among all tracked pollinators in cucumber and showed that insect pollination in cucumber acts as additional input in enhancing the yield [18].

Similarly, the highest weight of fruits, number of seeds per fruit, fruit size and TGW was achieved in honey bee pollination compared to others. Azmi et al. [19] observed heavier, longer and larger fruits in cucumber when pollinated by stingless bee (*Heterotrigona itama*) and hand compared to those produced from pollination without *H. itama*. Rouf et al. [20] reported an increase of 45.46 and 23.17% in seed yield of cauliflower plants pollinated by honey bee over plants grown inside net without bees and open pollination, respectively. Further, they showed that maximum yield attributes of seed could be achieved if planned bee pollination and central curd cutting employed together.
