OBJECTIVES OF PLANT BREEDING

The objectives of Plant Breeding vary depending on the specific goals and requirements of the breeders, but some common objectives include:

1. Higher Yields: Most of the breeding programmes aim at higher crop yields. In fact, higher yields will always remain one of the main objectives of breeding programmes. This is achieved by developing more efficient genotypes, eg, hybrid varieties.

2. Improved Quality: The quality of a plant produce determines its suitability for various uses. Therefore, quality is an important aspect for plant breeders. Quality characters vary from one crop to another, eg, grain size, colour, milling and baking qualities in wheat (Triticum aestivum); cooking quality in rice (Oryza sativa), etc.

3. Disease and Insect Resistance: Resistant varieties offer the cheapest, the most convenient, and environmentally safe method of disease and insect management. In some cases, they offer the only feasible means of control, eg, rusts in wheat.

4. Change in Maturity Duration: Breeding for early maturing crop varieties, or varieties suitable for different dates of planting may be an important objective in many crops. This would permit new crop rotations and often extend the crop area. For example, the development of wheat varieties suitable for late planting has permitted rice-wheat rotation.

5. Agronomic Characteristics: 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. 

6. Photo- and thermo-insensitivity: Development of photo insensitive and thermos insensitive wheat, and photo insensitive rice 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 Ppdl and Ppd2, which show polymeric gene action.

7. Synchronous Maturity: Synchronous maturity is highly desirable in crops like mung (Vigna radiata), where several pickings are necessary.

8. Non shattering Characteristics: This feature would be of great value in a crop like mung where shattering is a major problem in case of many commercial varieties.

9. Determinate Growth: Development of varieties with determinate growth habit is desirable in crops like mung pigeon pea (Cajanus cajan), cotton (Gossypium spp.), etc.

10. Dormancy: In some crops, seeds germinate even before harvesting if there are rains at the time of maturity, eg, mung, barley, etc. A period of dormancy in such crops would check the losses due to preharvest rains. But in some crops, it may be desirable to remove dormancy.

11. 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 now grown as summer crop in addition to the main kharif crop

12. Moisture Stress and Salt Tolerances: 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) soils in the country vary from 7 to 20 million hectares, of which about 28 million hectares are alkaline soils. Most of these areas are spread in the states of Uttar Pradesh, Haryana and Punjab.

13. Elimination of Toxic Substances: Some crops have toxic substances, which must be eliminated to make them safe for consumption. For example, khesari (Lathyrus sativa) seeds have a neurotoxin, B N-oxalyl-a-B-diamino propionic acid (HOAA) that causes paralysis of lower limbs. 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.

14. Crop uniformity and stability: Plant breeders strive to develop cultivars that exhibit uniformity in their traits and performance. Uniformity is important for commercial agriculture, as it facilitates mechanization, harvest efficiency, and consistent quality. Stability refers to the ability of a cultivar to maintain its performance across different environmental conditions and over time.

15. Genetic diversity preservation: Another objective of plant breeding is to preserve and enhance genetic diversity within crop species. This helps maintain a broad genetic base, which is essential for long-term breeding progress, resistance to evolving pests and diseases, and adaptation to future environmental changes.

These objectives of plant breeding are pursued through various breeding methods, including conventional breeding techniques, molecular breeding approaches, and genetic engineering, while considering ethical, regulatory, and safety aspects.

Reference: Principles of Plant Breeding (2022) - B D Singh