Role of Nature to encourage cross pollination and avoid self pollination- out breeding devices and Artifecial Hybridisation

• In Flowering plants, Continued self  pollination result inbreeding depressions or Hybrid vigour. 

• Therefore flowering plant has developed many devices to prevent self pollination and and enourage the cross pollination because cross pollination lead the genetic variabiliry  and it is an essential elements for the process of evolution. 

• There are various devices that are given by the nature to the flowering plants to encourage the cross pollination. 

• These devices are called as  outbreeding devices. 

Self incompatibility - 

• It is a condition where pollen of flower  either do not grow at all or group very slowly if they fall on the stigma. This situation prevents the self  pollination.

Dichogamy-  

• The maturation of pollen and stigma of a flower are not synchronised. 

• It means that time of stigma receptivity  and time of pollen release are different. This is called as Dichogamy. 

• When the stigma become receptive  before the release of pollen. This condition is called protogyny. 

• The Protogyny  condition can be seen in Magnolia, Aristolochia.

• When the pollen are release before the stigma became receptive. this condition is called Protandry. This can be seen in Salvia, Helianthus.

Herkogamy- 

• In some bisexual flower the structure anther and style is organised in such condition that  self pollination is not possible and you can say the anther and stigma are located at different position so pollen can  not come in contact with stigma. this condition is called Herkogamy.

• In caryophyllaceae, the style is much longer than stamen so  the pollen is fail to reach the stigma. 

• Similarly in Gloriosa, the anther release pollen at much distance from stigma. So there is no contact between pollen and stigma. 

• Besides these, the production of unisexual  flowers is is also a device that prevent self pollination. 

• Another device is occurrence of  diocious plant , In these  plant male and female flowers are originated on the different plants  so there is no chances for self pollination. For ex- Papaya.

Artificial Hybridisation :

• To get superior varieties of plant, plant breeders make effort to combine the desirable trait by crossing with superior varities. 

• Artificial Hybridisation is one of the approach to get superior breed under plant breeding programme.

• In such crossing, it is important that pollen grains must be used with superior plant with desirable characters. In addition to this , stigma is also protected from undesirable  or unwanted pollen grain.  Both methods can be done by the emasculation or bagging.

• If plant produce bisexual flowers than anthers are removed from flower before the Anther dehisence  by using a pair of forceps. This is called emasculation. 

• Emasculated flower is covered by suitable bag made up of butter paper to protected stigma from unwanted pollen grains.This is called bagging.

• When stigma recieve desired pollen grain of mature Anther or dusted by hand than flower are rebagged.

• There is no need of emasculation if plant produce unisexual flower.