🌱 Modes of Reproduction in Crop Plants

This lesson covers core principles and exam-focused points from this topic in plant breeding.

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Knowledge of the mode of reproduction and pollination is essential for a plant breeder,

because these aspects help in deciding the breeding procedures to be used for the genetic

improvement of a crop species. Choice of breeding procedure depends on the mode of

reproduction and pollination of a crop species.

Reproduction refers to the process by which living organisms give rise to the offspring of similar

kind (species). In crop plants, the mode of reproduction is of two types: viz. 1) sexual

reproduction and 2) asexual reproduction

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I. Sexual reproduction

Multiplication of plants through embryos which have developed by fusion of male and

female gametes is known as sexual reproduction. All the seed propagating species belong to this

group.

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Sporogenesis

Production of microspores and megaspores is known as sporogenesis. In anthers,

microspores are formed through microsporogensis and in ovules, the megaspores are formed

through megasporogenesis.

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Microsporogenesis

The sporophytic cells in the pollen sacs of anther which undergo meiotic division to form

haploid i.e., microspores are called microspore (MMC) or pollen mother cell (PMC) and the

process is called microsporogenesis. Each PMC produce four microspores and each microspore

after thickening of the wall transforms into pollen grain.

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Megasporogenesis

A single sporophytic cell inside the ovule, which undergo meiotic division to form

haploid megaspore, is called megaspore mother cell (MMC) and the process is called

megasporogenesis. Each MMC produces four megaspores out of which three degenerate

resulting in a single functional megaspore.

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Gametogenesis

The production of male and female gametes in the microspores and megaspores is known

as gametogenesis.

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Microgametogenesis

This is nothing but the production of male gametes or sperm. On maturation of the

pollen, the microspore nucleus divides mitotically to produce a generative and a vegetative or

tube nucleus. The pollen is generally released in this binucleate stage. The reach of pollen over

the stigma is called pollination. After the pollination, the pollen germinates. The pollen tube

enters the stigma and travels down the style. The generative nucleus at this phase undergoes

another mitotic division to produce two male gametes or sperm nuclei. The pollen along with

the pollen tube possessing a pair of sperm nuclei is called microgametophyte. The pollen tube

enters the embryo sac through micropyle and discharges the two sperm nuclei.

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Megagametogenesis

The nucleus of the functional megaspore undergoes three mitotic divisions to produce

eight or more nuclei. The exact number of nuclei and their arrangement varies from one species

to another. The megaspore nucleus divides thrice to produce eight nuclei. Three of these nuclei

move to one pole and produce a central egg cell and two synergid cells on either side. Another

three nuclei migrate to the opposite pole to develop into three antipodal cells.

The two nuclei remaining in the center, the polar nuclei, fuse to form the secondary

nucleus. The megaspore thus develops into a mature female gametophyte called

megagametophyte or embryo sac. The development of embryo sac from a megaspore is known

as megagametogeneis. The embryo sac generally contains one egg cell, two synergids with the

apparent function of guiding the sperm nucleus towards the egg cell and three antipodals which

forms the prothalamus cells and one diploid secondary nucleus.

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Fertilization

The fusion of one of the two sperms with the egg cell producing a diploid zygote is

known as fertilization. The fusion of the remaining sperm with the secondary nucleus leading to

the formation of a triploid primary endosperm nucleus is termed as triple fusion . The primary

endosperm nucleus after several mitotic divisions develops into mature endosperm, which

nourishes the developing embryo.

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II. Asexual reproduction

Multiplication of plants without the fusion of male and female gametes is known as

asexual reproduction. Asexual reproduction can occur either by vegetative plant parts or by

vegetative embryos which develop without sexual fusion (apomixis). Thus asexual reproduction

is of two types: viz. a) vegetative reproduction and b) apomixis.

Vegetative reproduction refers to multiplication of plants by means of various vegetative plant

parts. Vegetative reproduction is again of two types: viz. i) natural vegetative reproduction and

ii) artificial vegetative reproduction.

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Natural vegetative reproduction

In nature, multiplication of certain plants occurs by underground stems, sub aerial stems,

roots and bulbils. In some crop species, underground stems (a modified group of stems) give rise

to new plants. Underground stems are of four types: viz. rhizome, tuber, corm and bulb. The

examples of plants which reproduce by means of underground stems are given below:

Rhizome: Turmeric ( Curcuma domestica), Ginger ( Zingiber officinale)

Tuber: Potato (Solanum tuberosum)

Corm: Arvi (Colocasia esculenta ), Bunda ( C. antiquorum )

Bulb: Garlic ( Allium sativum), onion ( A. cepa)

Col1	Col2	Col3
Rhizome: Turmeric	Tuber: Potato	**Bulb: Onion **

Sub aerial stems include runner, sucker, stolon, etc. These stems lead to vegetative

reproduction in mint ( Mentha sp) rose, strawberry, banana, etc. Bulbils are modified forms of

flower. They develop into plants when fall on the ground. Bulbils are founding garlic.

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Artificial vegetative reproduction

Multiplication of plants by vegetative parts through artificial method is known as

artificial vegetative reproduction. Such reproduction occurs by cuttings of stem and roots, and

by layering and grafting. Examples of such reproduction are given below:

Stem cuttings: Sugarcane ( Saccharum sp.) grapes ( Vitis vinifera ), roses, etc.

Root cuttings: Sweet potato, citrus, lemon, etc. Layering and grafting are used in fruit and

ornamental crops.

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Apomixis

Apomixis refers to the development of seed without sexual fusion (fertilization). In

apomixis embryo develops without fertilization. Thus apomixis is an asexual means of

reproduction. Apomixis is found in many crop species. Reproduction in some species occurs

only by apomixis. This apomixis is termed as obligate apomixis . But in some species sexual

reproduction also occurs in addition to apomixis. Such apomixis is known as facultative

apomixis .

There are four types of apomixis: viz.

1. parthenogenesis, 2) apogamy, 3) apospory and 4) adventive embryony.

1. Parthenogenesis. Parthenogenesis refers to development of embryo from the egg cell without

fertilization.

2. Apogamy. The origin of embryo from either synergids or antipodal cells of the embryosac is

called as apogamy.

3. Apospory. In apospory, first diploid cell of ovule lying outside the embryosac develops into

another embryosac without reduction. The embryo then develops directly from the diploid egg

cell without fertilization.

4. Adventive embryony. The development of embryo directly from the diploid cells of ovule

lying outside the embryosac belonging to either nucellus or integuments is referred to as

adventive embryony.

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Summary Cheat Sheet

Quick Recall Points

• This lesson focuses on key plant breeding concepts, terminology, and exam-relevant applications.
• Review major definitions, classifications, and method-wise distinctions from the sections above.
• Revise tables and examples from this lesson for fast pre-exam recall.

Exam Traps

• Do not confuse similarly named breeding methods without checking their core selection logic.
• Pay attention to crop-specific examples because the same principle can behave differently by species.

References

1 source • [1]

[1]

Standard Plant Breeding Class Notes (GPBR211)

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