STD-12 UNIT-6 CHA-2
REPRODUCTION IN FLOWERING PLANT
IMPORTANCE OF CROSS POLLINATION & POLLEN-PISTIL INTERACTION
Importance of Cross Pollination
Advantages
- A number of plants are self - sterile , that is , the pollen grains cannot complete growth on the stigma of the same flower due to mutual inhibition or incompatibility , e.g. , many crucifers , solanaceous plants .
- Several plants are prepotent , that is , pollen grains of another flower germinate more readily and rapidly over the stigma than the pollen grains of the same flower , e.g. , Grape , Apple .
- Such plants of economic interest give higher yield only if their biotic pollinators like bees are available along with plants of different varieties or descent though every other input like adequate irrigation , fertilizers or cultural care might have been already provided , e.g .. Sunflower , Safflower , Mustard , Cucurbits , Almond , Cloves , Apple , Pear and related pomaceous plants .
- Cross pollination introduces genetic recombinations and hence variations in the progeny .
- Cross pollination increases the adaptability of the offspring towards changes in the environment .
- It makes the organisms better fitted in the struggle for existence .
- The plants produced through cross pollination are more resistant to diseases .
- The seeds produced are usually larger and the offspring have characters better than the parents due to the phenomenon of hybrid vigour .
- New and more useful varieties can be produced through cross pollination .
- The defective characters of the race are eliminated and replaced by better characters ,
- Yield never falls below an average minimum .
- It is highly wasteful because plants have to produce a lager number of pollen grains and other accessory structures in order to suit the various pollinating agencies .
- A factor of chance is always involved in cross pollination .
- It is less economical .
- Some undesirable characters may creep in the race .
- The very good characters of the race are likely to be spoiled .
Pollen - pistil interaction
- Pollen - pistil interaction is the group of events that occur from the time of pollen depo sition over the stigma to the time of pollen tube entry into ovule .
- It is a dynamic process which has checks at several places for promotion or inhibition of pollen growth .
- Knowledge of pollen - pistil interaction is helpful to plant breeders in manipulating pollen growth even in incompatible cases .
- Pollen growth can be observed by dusting pollen ( e.g. , Pea , Chickpea , Crotalaria , Balsam , Vinca ) on drop of 10 % sugar solution .
- Within 15-30 minutes pollen tubes will be observed to come out of the pollen grains.
- Pollen - pistil interaction is a safety measure to ensure that illegitimate crossings do not occur .
- Pollen grains of a number of plants may settle over a stigma .
- Only the right pollen belonging to same species would germinate while others fail to do so .
- Compatibility and incompatibility of the pollen - pistil is determined by special proteins .
- The compatible pollens are able to absorb water and nutrients from the surface of the stigma .
- They germinate and produce pollen tubes .
- Pollen tubes grow into the style .
- Their growth and path through the style are also determined by specific chemicals .
- Significance of Pollination.
- Pollination is a means of taking the male gametophyte for its growth near the female gametophyte .
- Pollen - pistil interaction determines the suitability of pollen for carrying out the pro cess of sexual reproduction .
- It has freed the seed plants from the dependance on external water during fertilization .
- It can be manipulated to produce pure lines as well as desired varieties .
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