Objectives of Plant breeding
Plant breeding aims to improve the characteristic of plants so that they become more desirable agronomically and economically. The specific objectives would vary greatly depending on the crop under consideration. Some of the main objectives of plant breeding may be summarized as follows.
Most of the breeding programmes aim at higher crop yields. This is achieved by developing more efficient genotypes, e.g., hybrid varieties of maize (Z. mays), sorghum (S. bicolor), bajra (P. americanum), etc.
The quality of plant produce determines its suitability for various uses. Therefore, quality is an important aspect for plant breeders. The quality characters vary from one crop to another, e.g., grain size, colour, milling and baking quality in wheat (Triticum aestivum) ; cooking quality in rice (Oryza saliva) ; malting in barley (I lordeum vulgare) ; size, colour and flavor of fruits ; keeping quality of vegetables ; protein content in cereals and legumes ; lysine content in cereals; methionine and tryptophan contents in pulses etc.
Disease and Insect Resistance
Resistant varieties offer the cheapest and the most convenient method of disease and insect control. In some cases, they offer the only feasible means of control, e.g., rusts in wheat. Resistant varieties not only increase production but also stabilise it.
Change in Maturity Duration
It permits new crop rotations and often extends the crop area. Development of wheat varieties suitable for late planting has permitted rice-wheat rotation. Thus breeding for early maturing crop varieties, or varieties suitable for different dates of planting may be an important objective.
Modification of agronomic characteristics, such as plant height, tillering, branching, erect or trailing habit etc., is often desirable. For example, dwarfness in cereals is generally associated with lodging resistance and fertilizer responsiveness.
Development of photoinsensitive and temperature insensitive wheat and photoinsensitive rice (0. sativa) varieties has permitted their cultivation in new areas. Rice is now cultivated in Punjab, while wheat is a major rabi crop in West Bengal.
It is highly desirable in crops like mung (Vigna radiata), where several pickings are necessary.
It would be of great value in a crop like mung.
Development of varieties with determinate growth is desirable in crops like mung, pigeon pea (Cajanus cajan), cotton (Gossypium), etc.
In some crops, seeds germinate even before harvesting if there are rains at the time of maturity, e.g., mung, barley, etc. A period of dormancy in such cases would check the loss due to germination. In some other cases, however, it may be desirable to remove dormancy.
Varieties for New Seasons
Traditionally maize is a kharif crop. But scientists are now able to grow maize as rabi and zaid crops. Similarly, mung is grown as a summer crop in addition to the main kharif crop.
Moisture Stress and Salt Tolerance
Development of varieties for rainfed areas and for saline soils would be helpful in increasing crop production in India. The major proportion (Ca. 70%) of the cropped area in the counts), is rainfed. The estimates of salt-affected (saline) soils in the country vary from 7 to 20 million hectares, of which about 2.8 million hectares are alkaline soils. Most of these areas are spread in the states of Uttar Pradesh, Haryana and Punjab.
Elimination of Toxic Substances
Some crops have toxic substances which must be eliminated to make them safe for consumption. For example, khesari (Lathyrus sativus) seeds have a neurotoxin, 13-N-oxalylamine alanine (BOAA) that causes paralysis. Similarly, Brassica oil has erucic acid which is harmful to human health. Removal of such toxic substances would increase the nutritional value of these crops.
Winter Hardiness would be desirable in certain situations.