Horticulture, pollination and fertilisation

1. Pollination
Refers to transfer of pollen grains from anther to stigma surface.
1. Self pollination: transfer of pollen from stamen to stigma of the same flower. If the
pollen grains ofsame variety reaches the stigma.
2. Cross pollination: if the pollen is to be transferred to the stigma of different flowers.
Either of the variety is different.
Autogamy- it is done without the aid of any outside agency such as wind, insect therefore highl,
self pollination eg. Tomato, French bean, pea etc.

2. ogamy- clfected with the aid of outside agency such as wind. insect therefore highly cross
llination cg. Incucurbits, colecrop ctc.
Factorsavouring sclf pollination
||1.
IV.
I.
1.
I.
III.
Cleistogamy : it is a condition in which flowers never open before anthcsis. The pollens
are shed whitin closed flowers and ncccssitates sclf pollination. It is common in grape.
papaya and sapota.
Homogamy: in this condition the stamen (male-androecium) and the carpels or pistils
(lemale= gynoccium) of the flowers mature at the same time. The prOcess enhances the
chance of pollination. Homogamous condition is secn in apricot, citrus, peach. and dwarf
coconut cultivars.
Factors favouring cross pollination
Geitonogamy: itsgreek word derived from geilon- neighbor and gamein- to marry. Thus
it is the process of pollination of flowers by another flower of sanme flowering plant. The
process interferes with sex function and leads to reduced outcrossing. For example
Orchids, Asclepias speciosa, Deodon verticillatus.
Monoecy: when male and female flowers are present on separate brancehes of the same
plant.This situation is known as monoecy and tye flowers are known as monoecius. It is
foundin banana, jackfruit, coconut, pecannut, hazelnut, walnut, cucrbits., pines etc.
Unisexuality: a floer is unisexual when ony one sex is present in it. It may be staminate
possessing stamens only or pistillate possessing caroels only. Eg papaya, date. palm.
grape etc.
Chasmogamy: the flowers are open and their reproductive organs Yre exposed toexternal
environment. They attrct bees, butterflies, moths, birds, bats, squirrels, animals. mankinds
and also subjected to the action ofwind and water. All such facors create congeniality to
cross pollination.
Self incompatibility - it is the inability of the otherwise functionalpollen to fertilise the
ovaryu ofthe same flower. It is oftwo type

3. IT PLA4NTS
flowering plant. The process interferes with sex function and leads to reduced
outcrossing.For example Orchids,Asclepias speciosa, Deodon verticillatus.
(iv)Monoecy. When male and female flowers are present on separate branches of the
same plant. this situation is known as monoccy and the flowers are known as
monoecious. It is found in banana, jackfruit, coconut, pecan nut, hazelnut, walnut,
cucurbits, pines etc. Under such situation geitonogamy is observed in which pollination
takes place between two different flowers located differently on the same plant.
Factors favouring cross pollination
()Unisexuality. Aflower is unisexual when only one sex is present in it. It may be
staminate possessing stamens only or pistillate possessing carpel only e.g. papaya, date
palm, grape (muscadine) etc.
() Chasmogamy. The flowers are open and their reproductive organs are exposed to
external environment. They attract bees, butterflies, moths, birds, bats, squirrels, animals,
mankinds and also subjected to the action of wind and water. All such factors create
congeniality tocross-pollination.
(iiy Self-incompatibility. It is the inability of the otherwise functional pgllen to
fertilize the ovary ofthe same flower. It is of two types :
(a) Sporophytic selfincompatibility. In this type of incompatibility, the pollen-pistil
relation is governed by the genotype of pollen producing plant. Smaller number of
alleles are involved in the phenomenon. It is noted in mango, aonla and cocoa.
(b) Gametophytic selfincompatibility. Acondition in which pollen grains are not able
to fertilize the ovule produced by aplant which carries the alleles similar to pollen.
grains. It is common in ber, loquat, apple, pear, apricot, almond, cherry and
pineapple.
(iv) Dichogamy. When stamens and pistils of flowers don't mature at a time, the
phenomenon is known as dichogamy and the flowers are known as dichogamous. It is of
two types :
(a) Protandry. When the stamens mature first than the carpel, it represents protandry
condition. It is found in walnut, coconut,sapota, passionfruit, soursop (Annona
muricata) etc.
(6) Protogyny. When the carpels mature first than the stamens, it is referred to as
protogyny condition. For example--Annona sp. except A. muricata, fig, banana,
plum,pomegranate, avocado etc.
(P) Duodichogamy. Acondition when two batches of male flowers are temporarily

4. 182
separated by a batch of female flower in between. the situation is
known as
duodichogamy. The resting period between flowering avoid selfing completcly.
(v)Heterodichogamny. It is state of having two genetically reciprocalmorphs whic
functionas afemale first, then as a male, the otherbehaving inopposite ways. It is
obterved in walnut, hazclnut Annona squamosa, Zizyphus jujuba, Cinnamomur
commiphora, etc.
(vi) Heterostyly/Herkogamy. It is a condition in which styles of two or more forms
orlength are found in a flower of same species. It is of two types, distyly (Fig. I1.3) arc
tristyly (ig. 114).
Distyly
(a) Pin type. In this type, style is longer than stamens. It is broad towards apex arz
narrower towards base. Plants with pin type of heterostyly set more seeds as they hav
exposed stigmas. It is found in pomegranate and sapota.
(b) Thrum type. Such plants possess flower with ashort style. The stamen is longe
than the style. Thrum type heterostyly flowers experience poor set setting as the stigr=
remains hidden inside the corolla tube. This form of style is found in almond.
Tristyly
(a) Pin type heterostyly
Corolla
Long style
Short stam1
Calyx
FIG. 11.3. Distyly flowers
Corolla
Long star=
(a) Long styled, medium and short stamens.
(b)Medium styled,'short and long stemens.
(c) Short styled, medium and long stemen.
Short siye
Calyx
(b) Thrum type heterostyly
Tristyly plants possess diferent types of flower with three different forms of
Each plant posseses one type of flower only. The different types of tristyly flow
detailed as under (Fig. 11.4) :

5. (vii) Male sterility: Presence of non-functional pollen grains in a flower favour the cross
pollination.Eg. Triploid banana, J.H. Hale cultivar of peach (peach is self pollinated except
this triploid pcach varicty etc.)
In maiority of horticultural crops pollination is affected by insects and pollination by wind is
wol comnon onc. Fruitslike sapota, jackfruit, aonla and crops like chestnut, walnut and
arecanut are reported to be pollinatcd by wind. They normally produce large pollen grains.
licht in weight so that thcy can be carried to different places. In these nut crops, the stigma is
also fcathery to facilitate wind pollination.
Honey bce,ants and many insectsaids in crosspollination. Theiractivity greatly affected by
weather condition especially low temperature and rain which sharply curtail their activity.
Hence honcybee keeping is important.
Fertilisation and Parthenocarpy:
Fertilisation: Union of male and female gamete in sexual reproduction is called
fertilisation, The pollen grains land on the sigma of the pistil it absorbs water and such
substance add sugar and forms pollen tube. This pollen tube grows down the style to the
embryo sac. The pollen tube penetrates the embryo sac where one male gamete unites with
the egg to form zygote (2n). After mitotic division the zygote becomes the embryo of the
resultant seeds. In angiosperms the other male gamete fuse with 2 polar nuclei ofthe embryo
sac and forms endosperm (3n) a nutritive tissue that supports the developing embryo. Thís
complete process is called double fertilisation.
Parthenocarpy: Formationof seedless fruit from ovary withoutpollination and
fertilisation. It is of 2 types
()
(ii)
Natural: (a) vegetative ie autonomic (b) stimulativeieaitionomic
Induced
Vegetative: It means the ability to set the fruit without the stimulus resulting from pollination
eg.Banana, pineapple, Washington naval orange and some varieties of fig and pear.
Stimulative: It means to develop seedless fruit only in response to stimulus external to ovary.
E.g Blackcarianth variety ofgrape, Allahabad Safeda guava.
Induced Parthenocarpy: Production of seedless fruits by treatment of flower with material
S/Adead pollen, pollen extract, chemicals/other growth substances is called induced
parthenocrpy. E.g. IBA, IAA and phenoxyacetic acid have been used to induce fruit drupe.
spray of 2,4-D, Gibberellic acid, 2,4,5-T NAA.Application of gibberellins to produce
parthenocarpic fruits yields better results than auxin.
Stenospermocarpy: process of formation of seedless fruits in which pollination an
fertilisation takes place but the embryo gets aborted subsequent e.g. grapes (Thompsom
seedless grapes).