The following are some of the main objectives:
1. Increased Production:
Plants are the main source of food for man either directly or indirectly. Even the animal foods like egg, butter, milk, meat etc are ultimately traceable to plants, hence the popular adage ‘All flesh is grass’.
The World agricultural output however is scarcely sufficient to feed the ever increasing human population. Even with improved methods of Agriculture, scientific cropping pattern, use of fertilizers, pesticides etc, there is always a food shortage in several countries of the third world. Besides the geopolitical reasons for such uneven distribution of food, there is also a genuine shortage. It is therefore no wonder that scientists are always looking for varieties and stocks of plants, with increased yield or production. Breeding programmed are undertaken to increase the per hectare yield in maize, rice, wheat and other cereals. If one can recall what, the King of Brabdingnong told Gulliver (in Gulliver’s Travels by Jonathan Swift) during his imaginary trip to that country.
(The King is supposed to have said that he would prefer a man, who make two blades of grass can grow, where one grew before than to anybody else); the same may be repeated as the aim and objective of the plant breeder. Just as in many other centre’s all over the world, in India also scientists at Indian Agricultural Research Institute, New Delhi, Central Potato Research Institute, Shimla, Regional Rice Research Institute, Cuttack, Sugarcane Research Institute, Coimbatore, and Agricultural Universities in all the Indian states have been engaged in the production of high yielding varieties.
The quality of plants in terms of height, size or shape is another character sought after by the plant breeder. Many of the garden plants are highly prized for their shape, density, size, bright color of the flowers, early blooming or late blooming etc. Similarly fruit size, nutritional quality, taste etc, are also qualities that are known to be improved by breeding. To mention one or two examples – Long staple cotton has been produced by crossing two varieties of Egyptian cotton. Similarly breeding has improved the sugar content in sugar beet from 7% to about 16%.
Sharbati sonora wheat is produced as a result of induced mutation in wheat (Sonora 64). This variety is known to have higher-protein content than sonora 64.
3. Resistance to Disease and Pests:
One of the greatest impediments for higher Agricultural output is the plant disease. A variety of causes bring about plant diseases. Fungi, bacteria, nematodes, insects and many other agencies cause untold havoc to agricultural output.
There have been instances where plant diseases have brought about a complete change in crop pattern or migration of people from one country to another in the years 1845-1847 there was virtual destruction of the potato crop in Ireland due to the late blight disease caused by Phytophthora fiestas. As a result many thousands of Irish people migrated to USA. Similarly the impact of coffee rust influenced plantations to switch over to Tea cultivation from coffee in Sri Lanka.
Plant breeders are constantly trying to evolve varieties which can impart genetic resistance to the diseases. In our country particularly, more than the high yielding varieties, disease resistance in crop plants is a primary necessity. In evolving disease resistant varieties, plant breeders usually choose a high yielding variety and cross it with a wild relative who is hardy and resistant. The resultant progeny in many instances will not only have a higher yield, but will also be resistant to the disease. Disease resistant wheat, sugar cane and many other crops have been evolved through breeding programmed. C250, C253 and C228 are wheat varieties resistant to yellow rust.
In grams (pulses) also – varieties G24, and G17 are resistant to gram wilt.
4. Varieties Suited to Particular Soils and Climates:
All crops cannot be cultivated in all types of soil and environmental conditions. It is essential therefore, that varieties, which are at home in a given environmental set up have to be evolved through breeding in order to achieve a higher yield.
For instance a particular variety may grow well in a hilly area, but may not grow well in plains. But by cross breeding; the same crop may be cultivated even in plains. The cultivation of groundnut was virtually unknown in Punjab during the early decades of this century. But a variety of groundnut PG. has been evolved and it is now cultivated extensively in Punjab in sandy soils. Some other new varieties of ground nut, with increased oil content are C117, C145, and C158 etc.
5. Varieties Resistant to Lodging:
Lodging means collapsing on the ground.
Many of the crop plants at the time of their maturity cannot withstand the weight either of the ears or fruits due to weak stem and collapse on the ground. This will greatly reduce the yield as the fruits or grains coming into contact with soil start decaying. The harvest also becomes difficult. Breeders try to evolve varieties, with strong stems or decreased height in order to prevent lodging a notable mention among wheat varieties which do not lodge in the Mexican dwarf.
Novel or Exotic Varieties:
Another trait, that the plant breeder is constantly looking for in any plant are unusual features. This is particularly so in horticultural or ornamental crops. Production of novel or exotic characters in plants will not only create a new variety, but also will be in great demand bringing economic benefits to the grower. Seedless grapes, seedless oranges and seedless pomegranates are some examples of novel varieties among the orchard crops.
Among the ornamental plants, new varieties of roses, Petunias, Hydrangia, Philodendrons, Authuriums, orchids etc commandm m a high price because of their attractive foliage or flower or both.