Hybridization Notes PDF

**HYBRIDIZATION** **Definition:** The mating or crossing of dissimilar genotype is known as hybridization. In plants, crossing is done by placing pollen grains from one genotype, called the male parent, onto the stigma of flowers of the other genotype, referred to as the female parent. It is essen...

**HYBRIDIZATION** **Definition:** The mating or crossing of dissimilar genotype is known as hybridization. In plants, crossing is done by placing pollen grains from one genotype, called the male parent, onto the stigma of flowers of the other genotype, referred to as the female parent. It is essential to prevent self-pollination as well as chance of cross pollination in the flowers of the female parent. At the same time it must be ensured that the pollen from desired male parent reaches the stigma of flower of the female parent for successful fertilization. **Objectives of Hybridization:** - To create genetic variation. - To transfer of one or more characters into a single variety from another variety (Combination Breeding). - To improve yield through transgressive breeeding. **Types of Hybridization:** Based on the taxonomic relationships of the parents involved, hybridization may be classified into two broad groups i). **Intervarietal:** The parents involved in intervarietal hybridization belong to the same species; they may be two strains, varieties or races of the same species. ii). **Distant hybridization** : includes crosses between different species of the same genus or of different genera. A. **Interspecific hybridization**: When two species of the same genus are crossed, it is known as interspecific hybridization. B. **Intergeneric hybridization**: When the species belong to two different genera, it is termed as inter generic hybridization. **Procedure of Hybridization:** There are seven steps involved in hybridization: I. Selection of parents II. Selfing of parents III. Emasculation IV. Bagging V. Tagging VI. Pollination/crossing VII. Harvesting and storage of seeds. I. **Selection of parents:** Desired plants are selected based on the expected objectives. The parents must be healthy, vigorous, disease free and available locally. II. **Selfing of Parents:** The selected parents are self fertilized for a number of generations in order to get 100% homozygosity. III. **Emasculation:** Emasculation is the process of removing male reproductive part (stamens) from a bisexual flower. This is usually done for preparing the female parents for hybridization. The main purpose of emasculation in to prevent self-pollination. Besides, it is done to mature flower buds which are expected to open on the following day. **Methods of emasculation:** a. Hand emasculation b. Suction method c. Hot water emasculation d. Alcohol treatment e. Cold treatment f. Genetic emasculation A. **Hand emasculation**: In species with relatively large flowers, stamens or anthers are removed with the help of forceps and scissors. It consists of the following steps i. Using a sterilised needle, the mature flower bud is open smoothly without causing any damage to the floral parts. ii. With the help of sterilised forceps or scissors the male reproductive parts, namely the stamens are carefully removed from the bud. During the process, any trace of stamens is not allowed to be kept inside the flowers. B. **Suction method:** This method is useful in species with small flowers. Emasculation is done in the morning just before or immediately after the flowers open. The petals are generally removed with forceps exposing the anthers and the stigma. A thin rubber or glass tube attached to a suction pump is used to suck the anthers from the flowers. The tube is also passed over the stigma to suck any pollen grains present on the stigma. C. **Hot water treatment**: Pollen grains are more sensitive than the female reproductive organs to both genetic and environmental factors. This property is used to kill the pollen grains with hot water or other agents like alcohol or cold water treatment without damaging the female reproductive organ. D. **Alcohol treatment:** It is not a commonly used method of emasculation**.** The method consist of immersing the flower or inflorescence in alcohol of a suitable concentration for a brief period. Followed by rinsing it with water. E. **Cold treatment:** Cold treatment, like hot water treatment, kills pollen grains without damaging gynoecium. In case of rice, treatment with cold water at 0-6° C kills pollen grains without affecting gynoecium. F. **Genetic emasculation:** Genetic or cytoplasmic male sterility may be used to eliminate the necessity of emasculation. IV. **Bagging:** Bagging is done in order to prevent contamination with other pollens. Bagging is usually done both in male and female parents. In female parents, bagging is done in order to prevent self-pollination and also to protect the flower from cross pollination. In male parents, it is done only for preventing contaminations with other pollens. While bagging , the following precautions must be taken 1. The bag should be transparent 2. The size of the bag should correspond to the size of the flower. 3. The bag should be provided with small holes for gaseous exchange. V. **Labelling or tagging:** Labelling is done in order to get correct details about the parents which are involved in hybridization. The following details are furnished on the labels. a. **Male parent:** Name of the plant, family, sex and name of the breeder. b. **Female parent:** Name of the plant, family, sex, date of emasculation, date of crossing, and name of the breeder. VI. **Pollination/Crossing:** It is the process of artificial pollination between unlike plants. During crossing, the mature, fertile and viable pollen grains collected from the protected male parent should be transferred to stigma of the desired emasculated female parent. Immediately after crossing the female flower is again bagged. VII. **Harvesting and storage**: The crossed heads or pods should be harvested and threshed. The seeds should be dried and properly stored to protect them from storage pests. Proper care should be taken to avoid contamination of the hybrid seed with other seeds. The seeds from each cross should be kept separately and, preferably, the seeds should be kept along with the original tags.