Apomixis in flowering plants is defined as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilization, leading to embryo development.
This power point Presentation intends to explore the different issues of incompatibility in angiosperms flower and the ways to overcome for desired benefits.
Pollen pistil interaction
Types of Incompatibility in plants
Methods to overcome Incompatibility
Prepared by
Dr. T. Annie Sheron
Assistant Professor of Botany
DEPARTMENT OF BOTANY
KAKATIYA GOVERNMENT COLLEGE, HANAMKONDA
Apomixis in flowering plants is defined as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilization, leading to embryo development.
This power point Presentation intends to explore the different issues of incompatibility in angiosperms flower and the ways to overcome for desired benefits.
Pollen pistil interaction
Types of Incompatibility in plants
Methods to overcome Incompatibility
Prepared by
Dr. T. Annie Sheron
Assistant Professor of Botany
DEPARTMENT OF BOTANY
KAKATIYA GOVERNMENT COLLEGE, HANAMKONDA
Polyembryony is the phenomenon of two or more embryos developing from a single fertilized egg. Due to the embryos resulting from the same egg, the embryos are identical to one another, but are genetically diverse from the parents.
The modes of reproduction in crop plants may be broadly grouped into two categories: asexual and sexual.
Sexual reproduction involves the fusion of male and female gametes, whereas in asexual reproduction new plants may develop from vegetative parts of the plant (vegetative reproduction) or may arise from embryos that develop without fertilization (apomixis).
SELF INCOMPATIBILITY IN VEGETABLES
Mode of pollination is very important in plant breeding because it determines the genetic constitution, nature of gene action, ease in pollination control and stability of varieties after release. There are several mechanisms that promote cross pollination, among these self-incompatibility. Self incompatibility is defined as the prevention of fusion of fertile (functional) male and female gametes of the same plant (Gowers, 1989). Self incompatibility is a system where self-recognition and rejection is the rule that prevents inbreeding depression.
Plant fertilization is the union of male and female gametes (reproductive cells) to produce a zygote (fertilized egg)
Double Fertilization
Both the male gametes/sperms participate in sexual reproduction.
Two male gametes fuse with one female gamete wherein one male gamete fertilizes the egg to form a zygote, whereas the other fuses with two polar nuclei to form an endosperm
Triple fusion is the fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm.
Porogamy - entry through the micropyle.
Chalazogamy - entry through the Chalaza
Mesogamy - entry through the middle part or the integuments
Steps leading to fertilization
Germination of the pollen grain:
Stigma function is to provide place of lodging and germination of the pollen grain after pollination.
Types of stigmas-
Wet stigmas
Secrete exudates like water and other nutrients
In the form of droplets on the stigma.
Exudates made up of a mix of water, lipids, sugars, amino acids, phenolic compounds.
Highly viscous and adhesive. Ex: Petunia, Zea etc.
Dry stigma
Do not secrete exudates Ex: Gossypium
Double Fertilization & Triple Fusion:
Both the male gametes are involved in the fertilization.
Fertilize two different components of the embryo sac - Double Fertilization
One fuses with the egg nucleus (syngamy) -> Zygote(2n)
second fuses with polar nuclei -> primary endosperm nucleus (PEN).
Involves fusion of three nuclei - Triple fusion -> Endosperm(3n)
Pollen tube in the synergids:
Entry only through micropyle. Guided by oburator
Presence of chemotropic substances
Collapse of one the synergids prior to entry of the pollen tube.
Pollen tube in the synergids:
Entry only through micropyle. Guided by oburator
Presence of chemotropic substances
Collapse of one the synergids prior to entry of the pollen tube.
Discharge of pollen tube contents (two male gametes, vegetative nucleus and cytoplasm) into the synergids.
Disorganization of tube nucleus
Polyspermy &Heterofertilization
Heterofertilization - Type of double fertilization in plants in which endosperm and embryo are genetically different.
This happens when two different sperm nuclei from two different pollen tubes happen to enter the same embryo sac.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Megasporogenesis is the process of formation of megaspores from the megaspore mother cell.
In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Self incompatibility in plants: a pollination control mechanism in plantsVijayakumar Narayanpur
Self incompatibility(SI) in plant plays important role in view of hybrid seed production. SI in this ppt have been explained in detail from its basics. The mechanism has been explained on the basis of conventional methods and molecular basis. It will be very useful for teaching and students.
Polyembryony is the phenomenon of two or more embryos developing from a single fertilized egg. Due to the embryos resulting from the same egg, the embryos are identical to one another, but are genetically diverse from the parents.
The modes of reproduction in crop plants may be broadly grouped into two categories: asexual and sexual.
Sexual reproduction involves the fusion of male and female gametes, whereas in asexual reproduction new plants may develop from vegetative parts of the plant (vegetative reproduction) or may arise from embryos that develop without fertilization (apomixis).
SELF INCOMPATIBILITY IN VEGETABLES
Mode of pollination is very important in plant breeding because it determines the genetic constitution, nature of gene action, ease in pollination control and stability of varieties after release. There are several mechanisms that promote cross pollination, among these self-incompatibility. Self incompatibility is defined as the prevention of fusion of fertile (functional) male and female gametes of the same plant (Gowers, 1989). Self incompatibility is a system where self-recognition and rejection is the rule that prevents inbreeding depression.
Plant fertilization is the union of male and female gametes (reproductive cells) to produce a zygote (fertilized egg)
Double Fertilization
Both the male gametes/sperms participate in sexual reproduction.
Two male gametes fuse with one female gamete wherein one male gamete fertilizes the egg to form a zygote, whereas the other fuses with two polar nuclei to form an endosperm
Triple fusion is the fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm.
Porogamy - entry through the micropyle.
Chalazogamy - entry through the Chalaza
Mesogamy - entry through the middle part or the integuments
Steps leading to fertilization
Germination of the pollen grain:
Stigma function is to provide place of lodging and germination of the pollen grain after pollination.
Types of stigmas-
Wet stigmas
Secrete exudates like water and other nutrients
In the form of droplets on the stigma.
Exudates made up of a mix of water, lipids, sugars, amino acids, phenolic compounds.
Highly viscous and adhesive. Ex: Petunia, Zea etc.
Dry stigma
Do not secrete exudates Ex: Gossypium
Double Fertilization & Triple Fusion:
Both the male gametes are involved in the fertilization.
Fertilize two different components of the embryo sac - Double Fertilization
One fuses with the egg nucleus (syngamy) -> Zygote(2n)
second fuses with polar nuclei -> primary endosperm nucleus (PEN).
Involves fusion of three nuclei - Triple fusion -> Endosperm(3n)
Pollen tube in the synergids:
Entry only through micropyle. Guided by oburator
Presence of chemotropic substances
Collapse of one the synergids prior to entry of the pollen tube.
Pollen tube in the synergids:
Entry only through micropyle. Guided by oburator
Presence of chemotropic substances
Collapse of one the synergids prior to entry of the pollen tube.
Discharge of pollen tube contents (two male gametes, vegetative nucleus and cytoplasm) into the synergids.
Disorganization of tube nucleus
Polyspermy &Heterofertilization
Heterofertilization - Type of double fertilization in plants in which endosperm and embryo are genetically different.
This happens when two different sperm nuclei from two different pollen tubes happen to enter the same embryo sac.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Megasporogenesis is the process of formation of megaspores from the megaspore mother cell.
In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Self incompatibility in plants: a pollination control mechanism in plantsVijayakumar Narayanpur
Self incompatibility(SI) in plant plays important role in view of hybrid seed production. SI in this ppt have been explained in detail from its basics. The mechanism has been explained on the basis of conventional methods and molecular basis. It will be very useful for teaching and students.
Events of fertilization
A] Pollination brings female and male gametophyte together- The male and female gametophytes must meet and unite their gametes to fertilize egg. This is done by pollination, in which pollen is placed on the stigma of the carpel.
B] Germination of pollen grain under suitable condition- The cytoplasm of the pollen grain absorbs sugar and water from the stigma and bulges out to produce a tube known as pollen tube by braking down exine of pollen grains. This germinating pollen tube grows down through the stigma and style of flower towards the micropyle of the ovary. This tube produces chemical, calcium such as that dissolves the tissues of the style and the tip of the pollen tube enters the ovary through the micropylar end occurring double fertilization.
Pollination brings female and male gametophyte together- The male and female gametophytes must meet and unite their gametes to fertilize egg. This is done by pollination, in which pollen is placed on the stigma of the carpel.
B] Germination of pollen grain under suitable condition- The cytoplasm of the pollen grain absorbs sugar and water from the stigma and bulges out to produce a tube known as pollen tube by braking down exine of pollen grains. This germinating pollen tube grows down through the stigma and style of flower towards the micropyle of the ovary. This tube produces chemical, calcium such as that dissolves the tissues of the style and the tip of the pollen tube enters the ovary through the micropylar end occurring double fertilization.
This slide serves as the completing part of BIO 101. It covers topics such as Basic reproduction, Genetics and heredity, ecology, evolution, animals and plants; lower and higher.
This file contains details on hydroponics system- a hi-tech farming method. It comprises of its history, advantages and disadvantages, types and some success stories which will help you to have a general idea on this topic
This file contains images of major pest of banana with their nymph/larva, adult and nature and symptom of damage on thr crop. Files are verified by the professor of Institute of Agricultural Sciences, SOA, Bhubneshwar.
This file contains images of major pest of coconut with their nymph/larva, adult and nature and symptom of damage on thr crop. Files are verified by the professor of Institute of Agricultural Sciences, SOA, Bhubneshwar.
This file contains images of larva, adult and damage symptoms caused by pests of some major and minor pests of citrus fruit. This will not only help in educational purposes but also in identification in field.
The file is verified by professors of institute of Agricultural Sciences, SOADU.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of black pepper and turmeric . It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
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This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of coffee. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of tea. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of onion. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of potato. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of pea. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
This file contains the images of larva, adult and damage symptoms of pests of brinjal. It will help you not only in yours Agriculture profession but also in identifying the pest in field condition.
This file is verified by professors of institute of Agriculture Sciences, SOA, Odisha.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
1. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 1
MODES OF REPRODUCTION IN CROP PLANTS
The modes of reproduction in crop plants may be broadly grouped into two categories, asexual and
sexual.
(A) ASEXUAL REPRODUCTION: Asexual reproduction does not involve fusion of male and female
gametes. New plants may develop from vegetative parts of the plant (vegetative reproduction) or
may arise from embryos that develop without fertilization (apomixis).
(i) Vegetative Reproduction: In nature, a new plant develops from a portion of the parent plant. This
may occur as follows.
1. Underground Stems: The underground modifications of stem generally serve as storage organs
and contain many buds. These buds develop into shoots and produce plants after rooting. Eg: Tuber:
Potato; Bulb: Onion, Garlic; Rhizome: Ginger, turmeric; Corm: Bunda, arwi
2. Sub-aerialStems: These modifications include runner, stolon, sucker etc. Sub-aerial stems are used
for the propagation of mint, date palm etc.
3. Bulbils: Bulbils are modified flowers that develop into plants directly without formation of seeds.
These are vegetative bodies; their development does not involve fertilization and seed formation.
The lower flowers in the inflorescence of garlic naturally develop into bulbils.
4. Artificial Vegetative Reproduction: It is commonly used for the propagation of many crop species,
although it may not occur naturally in those species. Stem cuttings are commercially used for the
propagation of sugarcane, grapes, roses etc. Layering, budding, grafting and gootee are in common
use for the propagation of fruit trees and ornamental shrubs. Techniques are available for vegetative
multiplication through tissue culture in case of many plant species.
Significance of Vegetative Reproduction: Vegetatively reproducing species offer unique possibilities
in breeding. A desirable plant may be used as a variety directly regardless of whether it is homozygous
or heterozygous. Further, mutant buds, branches or seedlings, if desirable, can be multiplied and
directly used as varieties. In many of the species sexual reproduction occurs naturally but for certain
reasons vegetative reproduction is more desirable.
(ii) Apomixis: In apomixis, seeds are formed but the embryos develop without fertilization.
Consequently, the plants resulting from them are identical in genotype to the parent plant. In
apomictic species, sexual reproduction is either suppressed or absent. When sexual reproduction
does occur, the apomixis is termed as facultative apomixis. But when sexual reproduction is absent,
it is referred to as obligate. Many crop species show apomixis, but it is generally facultative.
A simplified classification of apomixis is given below:
2. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 2
Significance of Apomixis: Apomixis is a nuisance when the breeder desires to obtain sexual progeny.
But it is of great help when the breeder desires to maintain varieties. Thus in breeding of apomictic
species, the breeder has to avoid apomictic progeny when he is making crosses or producing inbred
lines. But once a desirable genotype has been selected, it can be multiplied and maintained through
apomictic progeny. This would keep the genotype of a variety intact. Asexually reproducing crop
species are highly heterozygous and show severe inbreeding depression. Therefore, breeding
methods in such species must avoid inbreeding.
(B) SEXUAL REPRODUCTION: Sexual reproduction involves fusion of male and female gametes to
form a zygote, which develops into an embryo. In crop plants, male and female gametes are produced
in specialised structures known as flowers.
Flower: A flower usually consists of sepals, petals (or their modifications), stamens and/or pistil. A
flower containing both stamens and pistil is a perfect or hermaphrodite flower. If it contains stamens,
but not pistil, it is known as staminate, while a pistillate flower contains pistil, but not stamens.
Staminate and pistillate flowers occur on the same plant in a monoecious species, such as maize,
Colocasia, castor, coconut, etc. But in dioecious species, staminate and pistillate flowers occur on
different plants, e.g., papaya, date palm, pistachio etc.)
In crop plants, meiotic division of specific cells in stamen and pistil yields microspores and
megaspores respectively. This is followed by mitotic division of the spore nuclei to produce gametes;
the male and female gametes are produced in microspores and megaspores, respectively.
Sporogenesis: Productions of microspores and megaspores is known as sporogenesis. Microspores
are produced in anthers (microsporogenesis), while megsspores are produced in ovules
(megasporogenesis).
Microsporogenesis: Each anther has four pollen sacs, which contain numerous pollen mother cells
(PMCs). Each PMC undergoes meiosis to produce four haploid cells or microspores. This process is
known as microsporogenesis (Fig. 1). The microspores mature into pollen grains mainly by a
thickening of their walls.
3. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 3
Megasporogenesis: Megasporogenesis occurs in ovules, which are present inside the ovary. A single
cell in each ovule differentiates into a megaspore mother cell. The megaspore mother cell undergoes
meiosis to produce four haploid megaspores. Three of the megaspores degenerate leaving one
functional megaspore per ovule (Fig. 2). This completes megasporogenesis.
Fig.1. Microsporogenesis and microgametogenesis (a generalized scheme)
Gametogenesis: The production of male and female gametes in the microspores and the
megaspores, respectively, is known as gametogenesis.
Microgametogenesis: This refers to the production of male gamete or sperm. During the maturation
of 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. When the pollen lands onto the
stigma of a flower, it is known as pollination. Shortly after pollination, the pollen germinates. The
pollen tube enters the stigma and grows through the style. The generative nucleus now undergoes a
mitotic division to produce two male gametes or sperms. The pollen, along with the pollen tube, is
known as microgametophyte. The pollen tube finally enters the ovule through a small pore,
micropyle, and discharges the two sperms into the embryo sac.
4. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 4
Fig. 2. Megasporogenesis and megagametogenesis (generalized scheme)
Megagametogenesis: The nucleus of a functional megaspore divides mitotically to produce four or
more nuclei. In most of the crop plants, megaspore nucleus undergoes three mitotic divisions to
produce eight nuclei. Three of these nuclei move to one pole and produce a central egg cell and two
synergid cells; one synergid is situated on either side of the egg cell. Another three nuclei migrate to
the opposite pole to give rise to antipodal cells. The two nuclei remaining in the centre, the polar
nuclei, fuse to form a secondary nucleus. The megaspore thus develops into a mature
megagametophyte or embryo sac. The development of embryo sac from a megaspore is known as
megagametogenesis. The embryo sac generally contains one egg cell, two synergids, three antipodal
cells (all haploid), and one diploid secondary nucleus.
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 zygote divides
mitotically to produce a diploid embryo. The primary endosperm nucleus produces endosperm
through repeated mitotic divisions. During seed development, endosperm provides nutrition to the
developing embryo.
5. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 5
Significance of Sexual Reproduction: Sexual reproduction makes it possible to combine genes from
two parents into a single hybrid plant. Recombination of these genes produces a large number of
genotypes. This is an essential step in creating variation through hybridization. Almost the entire
plant breeding is based on sexual reproduction. Even in asexually reproducing species, sexual
reproduction, if it occurs, is used as an advantage, e.g., in sugarcane, potato, sweet potato etc.
6. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 6
ANTHESIS
• The first opening of a flower is known as anthesis, which generally occurs in the morning.
• In case of rice, a flower is enclosed by two boat-shaped bracts called lemma and palea. Petals
and sepals are represented by two small sac like lodicules. When stigmas become receptive,
the lodicules gradually swell and push the lemma and palea apart.
MODE OF POLLINATION
• Pollination refers to the transfer of pollen grains from anthers to stigmas.
• Pollen from an anther may fall on to the stigma of the same flower leading to self-pollination
or autogamy.
• When pollen grains from flowers of one plant are transmitted to the stigmas of flowers of
another plant by wind (anaemophily), water (hydrophily) or insects (entomophily), it is known
as cross-pollination or allogamy.
• A third situation, geitonogamy, results when pollen from a flower of one plant falls onto the
stigmas of other flowers of the same plant, e.g, in maize. The genetic consequences of
geitonogamy are the same as those of autogamy.
MECHANISMS PROMOTING SELF-POLLINATION:
The various mechanisms that promote self-pollination are generally more efficient than those
promoting cross-pollination. These mechanisms are briefly summarised below.
1. Cleistogamy: In such cases, flowers do not open at all. This ensures complete self-pollination
since foreign pollen cannot reach the stigma of a closed flower. Cleistogamy occurs in some
varieties of wheat, oats, barley and in a number of other grasses.
2. Chasmogamy: In some species, flowers open, but only after pollination has taken place. This
occurs in many cereals, such as wheat, barley, rice and oats. Since the flowers do open, some
cross-pollination may occur.
3. In crops like tomato and brinjal, the stigmas are closely surrounded by anthers. Pollination
generally occurs after the flowers open, but the position of anthers in relation to stigmas
ensures self-pollination.
4. In some species, flowers open, but the stamens and the stigma are hidden by other floral
organs. In several legumes, eg. pea, mungbean, urdbean, soybean and gram, the stamens and
the stigma are enclosed by the two petals forming a keel.
5. In a few species, stigmas become receptive and elongate through the staminal columns this
ensures predominant self-pollination.
MECHANISMS PROMOTING CROSS POLLINATION:
There are several mechanisms that facilitate cross pollination; these mechanisms are described
briefly.
7. FUNDAMENTALS OF PLANT BREEDING (PB-212)
PREPARED BY JAY KUMAR 7
1. Dicliny: Dicliny or unisexuality is a condition, in which the flowers are either staminate (male)
or pistillate (female). Dicliny is of two types, viz., (1) monoecy and (2) dioecy.
(a) Monoecy: Staminate and pistillate flowers occur in the same plant, either in the same
inflorescence, e.g., castor, mango, banana and coconut, or in separate inforescences, eg, maize.
Other monoecious species are cucurbits, walnut, rubber, grapes etc.
(b) Dioecy: In such species male and female flowers are present on different plants, ie, the plants are
either male or female, e.g, papaya, date palm, and spinach. In some cases, there are hermaphrodite
plants in addition to male and female plants, and a number of intermediate forms may also occur.
2. Dichogamy: Stamens and pistils of hermaphrodite flowers may mature at different times,
thereby, facilitating cross-pollination.
(a) Protogyny: In crop species like pearl millet, pistils mature before stamens.
(b) Protandry: In crops like maize and sugarbeet, stamens mature before pistils.
3. In lucerne or alfalfa, stigma is covered with a waxy film. The stigma does not become receptive
until this waxy film is broken by the visit of honey bees, which also effects cross-pollination.
4. A combination of two or more of the above mechanisms may occur in some species. For
example, maize exhibits both monoecy and protandry. This improves the efficiency of the
system in promoting cross-pollination.
5. Self-lncompatibility: It refers to the failure of pollen from a flower to fertilize the same flower
or other flowers on the same plant. Self-incompatibility (SI) is of two types: sporophytic and
gametophytic. In both the cases, flowers do not set seed on selfing. SI is common in Brassica
(mustard,rai,cauliflower). SI is highly effective in preventing self-pollination.
6. Male Sterility: Male sterility refers to the absence of functional pollen grains in
hermaphrodite flowers.