Determination of Mode of Pollination in Crop Plants
(Muhammad Wajid Javed, Muhammad Hamid Javed & Shumaila Rasool)
Pollination is very important mechanism and a vital step in the life of a plant leading to several kinds of variations. These variations are mainly utilized for several objectives in order to have desirable traits in plants. Before considering the determinants of pollination, it is better to understand its definition.
It is generally defined as “the transfer of pollen from male floret (stamen) to female floret (carpel) in the same or different flower, on the same or different plants”. This position of the flower on the same or different plant leads to different mechanisms of pollinations.
Determinants of Pollination:-
Mode of pollination in crop plants belonging to various families and species are defined by several factors. But few of them are considered to more important and helpful in this regard. These are mainly:
- Presence of pollinating agent
- Protendrous condition
- Chasmogamous condition
- Self incompatibility
- Protogynous condition
- Dichogamous condition
- Self compatibility
These factors or conditions that are enlisted above are mainly include flower modifications such as cleistogamy, protendrous condition, chasmogamous condition,self incompatibility,protogynous condition, dichogamous condition, self-compatibility etc. Before discussing the determinants of pollination, it necessary to understand different modes of pollination existed in crop plants.
Figure SEQ Figure * ARABIC 1 a typical floral structure
Mode of Pollination in Crop Plants:-
Normally, mode of pollination in plants especially in crops is categorized as:
- Self pollination
- Cross pollination
- Often cross pollination
These have a distinct role in bringing variation and desired characters in plants.
1. Self pollination (Autogmay) :-
This involves the transfer of pollens from the anther of stamen to the stigma of carpel in the same flower or different flowers on the same plants. This mainly has no or less chances of possessing varitations in plants population. In Self pollination, both flowers belong to same plant or same variety. Here, the role of different carrying media such as insects, water, wind etc is insignificant because they have no role in causing self pollination in flowers of various plants. Examples of plants possessing self pollination are: lentil, mung bean, soya bean, Daisy, China aster, lettuce, sorghum, proso millet, slender, wheat grass, rescue grass, wild rye, sand love grass, annual rye grass, Sudan grass etc.
In many plants, removal of hercogamy, dichogamy or self incompatibility must lead to Self pollination. Self pollination has a series of steps. Its main and first step is, late anthesis( rupture of anthers) and abrupt pollination, when cross pollination is not occurred . Another step is accidently self pollination. Autogamy is a consequence of devoiding out breed process. This also refers structure and place variation in flower for autogamy. Other step is pre-anthesis autogamy (bud pollination). Finally flowers are not opened and kept closed (cleistogamy) for the occurrence of self pollination.
This is a floral alternation refers to closing of flower at the time of pollination. When flower is closed, thus no other pollen from any other plant finds its way to pollinate this kind of flower. Hence causing self pollination. This is existed in transitional flowers which possesses decrease in number and size of florats.This (Cleistogamy may be of two types:
I. Ecological: this as in Lespedeza stipulaceae
II. Constitutional: this is taken place in Festuca microstachys. This is also present in some barley cultivars. In barley cultivars, it is may be due to poor lodicules.
b) Chesmogamic selfing:-
Chesmogamiy refers to the condition in which flowers are open at the time of pollination. It mainly leads to cross pollination but self-pollination also occurs. At anthesis absence of pollinating agent make self-pollination possible. e.g. Vetches (Vicia stiva)
2. Cross Pollination (Allogamy):-
When shifting of pollen from one flower to another flower on different plants occurs, this is known as “cross pollination” or “allogamy” Cross Pollination is a good tool in causing variation and producing desired traits in crop plants. The plants including this category are normally dioecious (possessing male and female florets on different Plants). e.g. Date palm. Presence of carrying agents or carrying media make the cross pollination possible, such as insects, water etc. Different examples of cross pollinated plants and their pollinating agents are given as follows:
Wind and insects
Except these other examples includes; poplar, willow, buffalo garss etc. Cross pollination is also impacted by some other factors e.g. flower has cleistogamic or chasmogemic floral modifications at the time of pollination.
2. Often Cross Pollination:-
This is also present in self pollinated crops/flowers but the level of cross pollintation exceeds 5%. e.g. cotton. Others are lima beans, pea, okra and sesame etc.
Different plants with their NCP (natural cross pollination) percentage are given below:-
NCP (natural cross pollination) percentage
Insects and humming bird
Bees and thrips
About 5 but some cvs upto 65
Often cross pollinated plants are mostly hermaphrodite (i.e. they have both male and female florets on the flower) such as okra, sesame, pea and broad bean etc.
Determinants of Pollination:-
Mechanism of pollination is determined by different floral modifications and factors. These can be elaborated as under:-
1. Presence of pollinating agent:-
There are various agent that are involved in the pollination activity of flowers. They are may be:
a) Insects (entomophilous)
b) Water (Hygrophilous)
c) Animals (Zoophilous)
d) air (Anemophilous)
If the intensity of these agents in a specific locality is greater, this normally cause cross pollination because there is more probability of pollens to move from one plant to another via these carriers. Its reverse case occurs in the absence of these agents (I.e. there are more chances of self pollination). In cotton and okra, presence of insects make cross pollination possible.
When flowers are closed at the time of self pollination, self pollination occurs generally. Because due to the closing of petals, any pollen from out side the flower finds no way to fall on stigma. Thus, cross pollination is impossible under this condition. Examples are; Lettuce (partly cleistogamic), Oat (largely cleistogamic), Triticale, Rhode grass (mostly cleistogamic) and mountain brome grass etc.
3. Protendrous Condition:-
Maturing of androecium (male florat) before gynoecium (female florat), is known as “Protendrous condition”. When stamen becomes mature ahead of stigma, this normally leads to cross or often cross pollination. e.g. Cotton (Gossypium arboreum), (G.barbadense), (G.hirsutum). But some rare cases implement self pollination, as Sesame (protendrous but staminal column facilitate self pollination.
4. Chasmogamous Condition:-
This is the condition which refers the opening of flowers at the time of pollination. when flower is open, it generally cause cross pollination because there is more probability of out-side pollens to fall on this flower.
5. Self Incompatibility:-
When the pollens from the same flower are fall on the stigma of that flower, stigma shows no response. This will lead to failure of self pollination, thus cross pollination is possible. This is mainly taken place in apricot, peach and nectarine.
6. Self Compatibility:-
This is the inverse case of Self incompatibility. Here, pollens of the same flower are able to show their response on the stigma of the same flower (i.e. pollens are capable of forming pollen tube and hence successive fertilization occurs). This generally happens in safflower and melon etc.
7. Protogynous Condition:-
This is the situation in which gynoecium matures before male part (androecium). This difference in their maturing time normally make cross pollination possible. It is due to the reason that pollen from any other flower can pollinate the stigma. Its prominent examples are; tomato but its flower and cone of anther cause self pollination.
8. Dichogamous Condition:-
This term is derived from two Greek words: “dicho” means separate and “gamous” means marriage. This refers to the ripening of male and female florats at different times. As no one floret in a position to mature when other has mature already (i.e. both mature at different time) so it usually make the possibility of cross pollination. Its common examples consist of oak.
There are some other factors of determination of mode of pollinton as heterostyle, male sterility and herkogamy etc. But from the above mentioned determinents it can be clearly visualized that mode of pollination is mainly determined by floral structure and its different botanical features. Other thing is that if self pollination in a flower gives adverse results, it reveals that flower is cross pollinated.
Shumaila Rasool Department of Agri. Entomology,