Pollination
The process by which pollen grains are transferred from anther
to stigma is reffered to the pollination.
Pollination is two types –
1.
Autogamy or Self pollination
2.
Allogamy or Cross pollination
Autogamy –
transfer
of pollen grains from the stigma of same flower is known as autogamy or self
pollination.
Autogamy is closed from of breeding.
Such species develop homozygous balance and do not exhibit
significant inbreeding depression.
Mechanism promotes self – pollination /-
1.
Bisexually
–
Presence of male and female organs in the same flower is known
as
Bisexually. The presence of bisexual flowers is a must for
self pollination. All the self pollinated plants have hermaphrodite flowers.
2.
Homogamy –
Maturation of anthers and stigma of a flower at the same time
is called homogamy. As a rule, homogamy is essential for self- pollination.
3.
Cleistogamy
– When pollination
and fertilization occur n unopened flower bud, it is known as cleistogamy. It ensures
self pollination and prevents cross pollination. Cleistogmay has been reported
in some varieties of wheat, barley, oats and several other grass species.
4.
Chasmogamy
:- Opening of flowers only
after the completion of pollination is known as chasmogamy.
This also promotes self pollination and found
in crops like wheat m barley , rice and oats.
5.
Position
of Anthers /- In some species, stigma are surrounded by anthers
in such a way that self pollination is ensured. Such situation found in omato
and brinjal.
In some legumes, the stamens and stigma are
enclosed by the such a way that self pollination is ensured. Examples are
greengram, blackgram, soyabean, chickpea, and pea.
Allogamy
or Cross Pollination ;-
Transfer of pollen grains
from the anther of one plant to the stigma of the another plant is called
Allogamy or cross pollination.
This is the common from of the breeding. Allogamy leads to the
heterozygosity. Such species develop heterozygous balance and exhibit
significant inbreeding depression on selfing.
Mechanism
of Promoting Cross – pollination –
1.
Dicliny –
It
refers to unisexual flowers. This is two types
a.
Monoecy –
when
male and female flowers are separate but present in the same plant. It is known
as monoecy. In some crops, the male and flower are present the same
infloresence such as in mango, castor and banana.
b.
Dioecy – When staminate
and pistillate flowers are present on different plants, it is called dioecy. It
include, papaya, date , palm, spinach and asparagus.
2.
Dichogamy
– (greek word dikho- apart and gamous – marriage)
It refers to maturation of anthers and stigma of the same flowers
at different times, dichogamy promotes cross pollination even in the
hermaphrodite species.
Dichogamy is of two types
a.
Protogyny
:-
when pistil matures before anthers, it is called protogyny such as in pearl
millet.
b.
Protandry
;- When
anthers matures before pistil, it is known as protandry. It is found in maize,
sugarbeet and several species.
3.
Heterostyly
;-
When styles and filaents in a flower are of
different lengths, it is called heterostyly. It promotes cross pollination,
such as linseed.
4.
Herkogamy
;-
Hinderance to self- pollination
due to some physical barriers such as presence of hyline memebrane around the
anther is known as herkogmay.
Such member does not allow the dehiscence
of pollen and prevents self- pollination such as alfalfa.
