this presentation is prepared to explore basic knowledge about reproduction in field and horticultural crops.

1. Prepared By: Prof. T.V.Rathod

2. MODE OF REPRODUCTION
• Mode of reproduction determines the genetic constitution of
crop plants, that is, whether the plants are normally
homozygous or heterozygous.
• A knowledge of the mode of reproduction of crop plants is
also important for making artificial hybrids.
• Production of hybrids between diverse and desirable parents
is the basis for almost all the modern breeding programmes.
• The modes of reproduction in crop plants may be broadly
grouped into two categories, asexual and sexual.

3. Asexual Reproduction
 Vegetative Reproduction
• In nature, a new plant
develops from a portion of
the plant body. This may
occur through following
modified forms,
1. Natural vegetative
• Underground stem
• Sub-aerial stems
• Bulbils
2. Artificial vegetative
• Stem cuttings
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).
 Apomixis
• seeds are formed but the
embryos develop without
fertilization.
1. Parthenogenesis
2. Apospory
3. Apogamy
4. Adventive Embryony

6. Natural vegetative
• 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.
• Sub-aerial Stems
• These modifications include
runner, stolon, sucker etc.,.
• Sub-aerial stems are used for
the propagation of mint, date
plam etc.
• 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.
• Scientists are trying to induce
bulbil development in plantation
crops by culturing young
inflorescence on tissue culture
media ; it has been successfully
done in the case of cardamom.

7. Artificial vegetative
• 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, and attempts are being made to
develop the techniques for many others.
• In many of these species sexual reproduction occurs naturally but for
certain reasons vegetative reproduction is more desirable.

8. 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.

9. Apomixis
• In apomixis, seeds are formed but the embryos develop without
fertilization. (without the fusion of male & female gametes).
• 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. But when sexual reproduction is absent, it is
referred to as obligate.
• Many crop species show apomixis, but it is generally facultative.
• The details of apomictic reproduction vary so widely that a
confusing terminology has resulted.

12. • Parthenogenesis
• The embryo develops from embryo
sac without pollination. It is of two
types
 Gonial parthenogenesis – embryos
develop from egg cell,
 Somatic parthenogenesis –
embryos develop from any cell of
the embryo sac other than the egg
cell.
• Apospory
• The embryo may develop from egg
cell or some other cell of this
embryo sac.
• Apospory occurs in some species
of Hieraceum, Malus, Crepis,
Ranunculus, etc.
o Diplospory
• Embryo sac is produced from the
megaspore, which may be haploid
or, more generally, diploid.
• Apogamy
• In apogamy, synergids or
antipodal cells develop into an
embryo.
• Like parthenogenesis, apogamy
may be haploid or diploid
depending upon the haploid or
diploid state of the embryo sac.
• Diploid apogamy occurs in
Antennaria, Alchemilla, Allium
and many other plant species.
• Adventive Embryony
• In this case, embryos develop
directly from vegerative cells of
the ovule, such as nucellus,
integument, and chalaza.
• Development of embryo does not
involve production of embryo
sac.
• Adventive embryony occurs in
mango, citrus, etc.

15. Significance of Apomixis
• Apomixis is a nuisance when the breeder desires to obtain sexual
progeny, i.e., selfs or hybrids.
• It is of great help when the breeder desires to maintain varieties.
• 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.
• Asexually reproducing crop species are highly heterozygous and show
severe inbreeding depression.
• Therefore, breeding methods in such species must avoid inbreeding.

16. SEXUAL REPRODUCTION
• Sexual reproduction involves fusion of male and female gametes
to form a zygote, which develops in to an embryo.
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 thr ough
hybridization.
• Almost the entire plant breeding is based on sexual
reproduction.
• Even in asexually reproducing species, sexual reproduction, if it
occurs, is used to advantage, e.g., in sugarcane, potato, sweet
potato etc.

17. MODES OF POLLINATION
• Self-pollination
• Bisexuality
• Cleistogamy.
• Homogamy
• Chasmogamy
• Position of anthers in relation to
stigma.
• Genetic Consequences of Self-
Pollination
• Self-pollination leads to a very
rapid increase in homozygosity.
• Therefore, populations of self-
pollinated species are highly
homozygous.
• Self-pollinated species do not
show inbreeding depression, but
may exhibit considerable
heterosis.
• Therefore, the aim of breeding
methods generally is to develop
homozygous varieties.

19. • Cross-Pollination
• Unisexuality (Dicliny)
 monoecy
 dioecy
• Dichogamy
 protogyny
 Protandry
• Heterostyly
• Herkogamy
• Self incompatibility
• Male sterility
• Genetic Consequences of Cross-
Pollination.
• promotes heterozygosity in a
population.
• highly heterozygous and show
mild to severe inbreeding
depression and considerable
amount of heterosis.
• Usually, hybrid or synthetic
varieties are the aim of breeder
wherever the seed production of
such varieties is economically
feasible.
# Often Cross Pollination #