An improved variety of a crop is superior to the other existing varieties in respect to one or more characters. A crop variety must possess several desirable characters like, high yield, superior quality, early maturity, resistance to important diseases and insect pests, etc. There are two major methods of obtaining an improved variety of a crop. (i)HYBRIDIZAITON
It is the most common method of incorporating desirable characters into crop varieties. “Hybridization” refers to a cross between genetically dissimilar plants. It involves: 1.Selection of parents, one used as female and other as male. 2.Before the flowers of the female parent open, their anthers are carefully removed, this is called emasculation. This prevents self-pollination in bisexual flowers. 3.Pollens from the flowers of the male parent are placed on the stigma of emasculated flowers. 4.Seeds produced by the flowers of the female parent are hybrid seeds. (ii)Genetic engineering– it is the deliberate introduction of a gene that provides the desired characteristic and results in genetically modified crops (GM crops). (iii)Other methods of obtaining new, genetically different variety are- 1.Mutation 2. Domestication3. Plant introduction
A breeder selects from a population, those plants that have desirable characteristics. Seeds from only the selected plants are harvested and used to raise the next generation. Rests of the plants are rejected. This process is called selection and is the step that brings about improvement in the crop. Therefore, the extent of improvement in a character depends mainly on the effectiveness of selection.
FACTORS FOR WHICH IMPROVEMENT IN VARIETY IS DONE
It refers to the increase in production of the crop per acre. For new varieties to be accepted, it is necessary that the variety produce high yield under different conditions in different areas. The farmers need to be provided with good quality seeds, of a particular variety, which should germinate under the same conditions. 2.IMPROVED QUALITY
Quality considerations of crop products vary from crop to crop. The quality of a crop-produce includes all those characters that determine whether it is suitable for various uses. For examples, fruit size, colour, shape, flavor, taste, etc. are important quality characters in tomato, apple and other fruits. Similarly, baking quality is important in wheat; protein quality in pulses; oil quality in oilseeds.
3.BIOTIC AND ABIOTIC RESISTANCE
It aims to provide resistance against certain biotic (diseases, insects and nematodes) and aboitic (drought, salinity, water logging, heat, cold and frost) stresses.
4.CHANGE IN MATURITY DURATION
The high-yielding varieties of crops take less time for maturing than the traditional varieties of crops. This has the following benefits: (i)Allow farmers to grow multiple rounds of crops in a year. (ii)Short duration reduces the cost of crop production,
(iii)Uniform maturity makes the harvesting process easy and reduces loss during harvesting.
The improved variety should be able to grow in diverse climatic conditions. This helps in stabilizing the crop production under different environmental conditions. 6.DESIRABLE AGRONOMIC CHARACTERISTICS
Certain specific features of crops need to be improved. For example, fodder crops are more useful if they are tall and profusely branched, whereas, cereals are desired to be short (dwarf variety) so that fewer nutrients are consumed and the plants can withstand strong winds.
Plants require certain mineral elements for their normal growth, development and flourishment. These are called as plant nutrients. There are about 30 to 40 elements found in plants but only 16 of these are essential for better growth and development of plants. The 16 elements found essential for growth and development of plants are (i) Carbon, (ii) Hydrogen,...