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(a) Hybridization is the process of combining different varieties of organisms to create a hybrid. It is the method of producing a new crop in which two or more plants of unlike genetical constitution are crossed together.

Hybridization Procedure : The various steps in hybridization are as follows:

1. Selection of Parents : The first step in hybridization is to select the plants which are to be used as parents and can supply all desired characters.

2. Selfing of parents : This is the second step which involves artificial self-pollination of parents. It is essential for eliminating undersirable characters and obtaining onbreds.

3. Emasculation : Emasculation is the third step in hybridization procedure. The process of removal of stamens from female parent before they have burst and shed their pollens is called emasculation. The main purpose of emasculation is to prevent self-fertilization, that is why stamens are removed before the anthers ripe, dehisce and self-pollinate the stigma. Young flower buds which are yet to open are selected for emasculation.

4. Bagging : This is the fourth step in hybridization. Both male and female flowers are bagged separately to prevent contamination in staminate flowers and cross pollination in pistillate flowers. The bags are made usually of paper, cloth, plastic or cellophane.

5. Crossing : Crossing is the artificial cross-pollination between genetically unlike plants: In this process, viable pollens are collected from desired male parent and transferred to the stigma of desired emasculated female parent. Pollens are collected in petri dishes or paper bags and are immediately brushed or dusted on the stigma of emasculated female flower, which is bagged immediately.

6. Raising F1 generation : In this step, mature seeds of F1 generation are harvested, dried and stored. In the next season, these seeds are sown separately to raise the F1 generation. The plants obtained from F1 generation are called hybrids.

(b) 

Disease	Causative agent	Preventive measure
Amoebiasis	Entamoeba histolytica	Maintaining proper hygiene
Rabies	Rabies virus or Rhabhidovirus	Vaccinations of animals
Pneumonia	Streptococcus pneumoniae	Practicing proper hygiene and getting immunised

(c) Manures are the organic substances obtained by the decomposition of animal wastes and plant residues which supply essential elements and humus to the soil. They are added mainly to improve the physical conditions of the soil, to replenish and keep up its humus status, to maintain optimum conditions for the activities of soil micro organism. They help to supply all the elements of fertility which crops require in adequate proportions.

Types of manures :-

(i) Composted Manures : Composting is the process of vegetable and animal refuse to a quickly utilizable condition for improving and maintaining soil fertility.

(ii) Farmyard Manures : Good quality Farmyard manures is however the most valuable organic matter for the soil. . It consists of a mixture of cattle dung, the bedding used in the stable and remnants of straw and plant stalks fed to cattle. Partially rotten manures are generally applied to the soil.