Plant breeding is a science based on principles of genetics and cytogenetic. It aims at improving the genetic makeup of the crop plants.
Improved varieties are developed through plant breeding. Its objectives are to improve yield, quality, disease-resistance, drought and frost-tolerance and important characteristics of the crops.
Objectives of Plant Breeding:
Plant Breeding aims to improve the characteristics of plant so that they become more desirable agronomically and economically. Thus, the chief objective of plant breeding is to develop such improved varieties of crop plants that will be commercially successful. Generally, “a successful variety is one with total balance of traits that makes it more profitable for growers than any other one they might choose. This is why breeders are wary about emphasizing one trait to the exclusion of others’’.
(Lewis and Christiansen,1982). However, improvement in some specific traits of certain crops may become a priority objective for various agronomic, economic, etc. reasons. Therefore, specific objectives would very greatly depending on the crop under consideration. Some of the main objectives of plant breeding may be summarised as follows.
Most of the breeding programmes aim at higher crop yield. This is achieved by developing more efficient genotypes. E.g. Hybrid varieties of maize (Zeamays), Sorghum, (S.bicolar), bajara( P. amercanum), etc.
The quality of plant produce determines its suitability for various uses. Therefore, quality is an important aspect for plant breeders. Quality characters very from one crop to another, E.g. Grain size, colour, miling and baking qualities in wheat( Triticum aestivum ) ; cooking quality in rice( Oryza sativa); malting quality in barley( Hordeum vulgree) , size , colour, and flavour 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 management. 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 plating 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 in many cases.
Modification of agronomic characteristics, such as, plant height, tillering, branching, erect or trailing habit, etc is often desirable. For example, dwarfness in cereals in generally associated with lodging resistance and fertilizer responsiveness.
Development of photoinsensitive and thermosesitive wheat, and photoinsensitive rice (O.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. In case of Wheat, photoperiod insensitivity is due to genes Ppd1 and Ppd2(Polymeric gene interaction).
Synchronous maturity is highly desirable in crops like Mung (Vigna radiata) , where several pickings are necessary.
It would be of great value in crop like mung where shattering is a major problems in case of many commercial varieties.
Developments of varieties with determine growth is desirable in crops like Mung, Pigeon pea, cotton, etc.
In some crops, seeds germinate even before harvesting, the 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.
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 country is rainfed. The estimates of salt- affected (Saline) sols in the country vary from 7 to 20 million hectare, 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 (Lathyruys sativus) seeds have a neurotoxin, B-N-oxalyl- alfa, Beta-diaminopropionic acid (BOAA) that cause paralysis. Similarly, Brassica oil has cruic acid, which is harmful to human health. Removal of such toxic substances would increase the nutritional value of these crops.