Pollination (birds/insects/animals)

Zoophily is a form of pollination whereby pollen is transferred by animals.

• Flower should be colourful
•  Have fragnance/foul smell
• Nectar
• sticky pollen grains
• odoured flowers if pollinated by flies and beetles

Floral reward for insects:-

1.Safe place to lay eggs
2.Pollen or nector
3. Yucca and pronuba moth

Pronuba moth and yucca plant

Steps taken as follows :-

• so, firstly pronuba moth lay its egg in locule of the ovary of yucca plant.
• In turn flower get pollinated.
• both of them can’t complete their life cycle without each other.
• the larvae of the moth come out of the eggs.
• After hatching egg larvae feed on yucca seeds.
• Larvae then burrow out of the fruit.
• then it moves under the soil & make their cocoons.

pollen/nector robbers- Insects which consume pollen or nector without bringing about pollination. example-queen of bombus affinis

Out breeding devices

Devices or features of plants which discourage self pollination and encourage cross pollination are called as out breeding devices It prevent inbreeding depression which may be a result of continued self-pollination.
1.Unisexuality – formation of unisexual flowers two conditions are there –

a) Monoecious plants – male and female flowers are produced on plant .This prevent autogamy but not geitnogamy example- castor, maize

b) Dioecious plants – male and female flowers are example- papaya, vallisneria ducat e produced on two separate plants. It prevents autogamy as well as geitnogamy example- papaya, vallisneria

2.Dichogamy- different maturation time of androecium and gynoecium in the same flower. Either the pollen is released before the stigma becomes receptive much before the release of pollen.

3.self-incompatibility- the failure of the pollen grains from fertilizing the ovule by habiting pollen germination or pollen tube growth in the pistil. It is a genetically controlled mechanism.

4. In some species, the anther and stigma are placed at different position, so that pollen cannot come in contact with the stigma of the same flower.

Pollen-Pistil Interaction

➤ Pollination does not guarantee the transfer of the right type of pollen on stigma.

All pollinations do not lead to a successful fertilization because for a successful fertilization, pistil of a flower has to recognize the pollen of same species. Therefore, interaction between pollen grains and stigma needs to be understood properly. Once compatible pollen is accepted by pistil, events for fertilization proceed, whereas incompatible pollens are rejected. This interaction where a pistil is capable of recognizing its pollen is the result of long term pollen-pistil interaction and chemicals released by pollen.

Events of pollen-pistil interaction:-

1.Landing of true pollen on compatible pistil.
2.Germination of pollen and formation of pollen tube where pollen grains release its contents.
3.Pollen tube growth through style of the pistil towards the ovary.
4.Entry of male gametes into the ovule and then to synergid.

Entry of pollen tube into ovule takes place through:

1. Micropyle :- This is the most commen condition and takes place in most of the flowering plants
2. Chalaza: eg-casuarina
3. Integuments:- eg- cucurbita

Entry of pollen tube into Embryo sac:-

1. The tube invariably enters embryo sac at microplyar end i.e. cell. Cingve degenerating syner
2.Filiform apparatus present at micropylar part of synergids guide the entry of pollen tube.
3. All these events from pollen deposition on the stigma until pollen tube enters the ovule are together referred as pollen pistil Interaction.

Artificial hybridization

It is a method of crop improvement in which crosses are made b/w different varieties, species and genera, in order to combine the desirable characters in a single superior variety. This helps to avoid unwanted pollen rejection and saves time.
Hybridization proceeds in two steps, one is emasculation and another is bagging:-

1. Emasculation-Removal of stamens or anthers or killing the pollen of a flower without the female reproductive organ is known as emasculation.

2.Bagging: Bagging is the protection of emasculated flower from contamination by undesirable pollen grains. Here the flower is masked by a bag, still, the flower attains receptivity. In unisexual flowers, bagging is done before the flowers are open.