What is plant breeding?
Plant breeding is a discipline of applied plant science that deals with the improvement of crop plants through the production of hybrid crop plants, which are superior to the original plant varieties.
Importance of Plant Breeding
i) It produces more productive crop plants and there by improves food production.
ii) It can produce crop plants with superior features like fruit or grain size, vitamin content etc.
iii) It can generate disease resistant crop plants as for example rice plant against blight disease, tomato against wilt disease or sugarcane against red rot disease
iv) Plant breeding may also lead to the tolerence against extreme dryness or wetness.
v) It helps in the stabilization of a character in a particular crop plant.
vi) It results in the production of new varieties of crop plants.
vii) It results in the expression of heterosis or hybrid vigour.
viii) It involves the adaptation or acclimatization of a plant species to changing environmental conditions.
What is Hybridization?
It is a method plant breeding by which two plant varieties belonging to two different constitutions are crossed together to produce new crop varieties.
Types of Hybridization
On the basis of the nature of the crop plants crossed, hybridization can be of the following types:
i) A cross between two plants belonging to the same variety called Intra-varietal hybridization.
ii) A cross between two plants belonging to different varieties called Inter -varietal hybridization.
iii) A cross between two plants belonging to the same species called Intra-specific hybridization.
iv) A cross between two plants belonging to two different species Inter-specific hybridization.
v) A cross between two plants belonging to two different genera called Inter-generic hybridization.
Aims of Hybridization
For the plant breeding different aims of hybridization are as follows :
(i) To produce new varieties of crop plants.
(ii) To bring about variations in a particular group of plants,
(iii) To combine the good characters of two different plants in a single plant,
(iv) To exploit the principle of hybrid vigor, i.e., to produce a plant variety, which is superior to both the parents.
The actual process of hybrid plant breeding includes the following phases:
i) Selection of parent plants
ii) Selfing of plants
iii) Method of Hybridization
iv) Harvesting of Hybrid seeds.
Selection of parent plants
The parental crop plants are selected in such way that it is ensured that they are healthy, -they should be pure, that is they are not contaminated with foreign pollen grains. The desired characters must be present in those plants.
Selfing of plants
The plants are selfed i.e., artificially self-pollinated in order to eliminate undesirable characters. In plants showing self-pollination, the process is very simple but for those plants, where cross-pollination is possible, they are covered with a polythene bag called begging.
Method of Hybridization
The process of hybridization involves the steps of emasculation, bagging, crossing and labelling. The details of this process are as follows:
The process of emasculation involves the removal of stamens from intact flowers-, hence, cross-pollination becomes inevitable. The process of emasculation can be carried out in the following ways:
(a) Forceps Method: - The process involves the removal of stamens from an intact flower with the help of a pair of forceps or scissors. This is carried out in large flowers like paddy, pea etc.
(b) Hot water treatment: - In case of small flowers like millets, Sorghum, the stamens are too small to be removed with the help of forceps, hence the panicle is dipped in warm water at 45°C for 10 minutes, which inactivates the anthers.
(c) Male Sterility method: - In plants like barley, onion, the male sterile lines are used, whore the
sterile in nature and cannot produce functional pollen grains. The male sterile lines are obtained by the spraying of artificial phytohormones.
The male or female plants are covered with cellophane, polythene or paper bags to prevent contamination by foreign pollen grains in male plant and cross- pollination in female plants. These bags are made porous for the purpose of aeration. The bags in case of male plants are removed after the pollen grains are shaded off and used for artificial pollination. But in case of female plants, the bags are kept for a longer period.
After the anther gets matured, they shed off the pollen grains in the male plant. These are collected in cellophane bags or Petri plates and are rubbed on the stigma of emasculated female plant by removing the bag. After crossing, the bag is again tied and maintained till seed setting is completed. The process of crossing is mostly carried out in the morning hours, when the stigma is receptive towards pollen grains.
The labeling is done for plant breeding with a tag attached to the crossed plant. It should contain the relevant information like details of parent plants, date of emasculation, date of bagging and crossing, field reference number etc.
Harvesting of Hybrid seeds
After the seeds are matured, the bags are removed, the seeds are harvested and collected in labeled envelope. They are preserved carefully and used in the next growing season for hybrid plant breeding.