What is Plant Breeding?

Plant breeding is the deliberate, purposeful manipulation of plant species to create new plant types that are better suited to cultivation, give higher yields, and resist disease.

People have practised plant breeding, in a conventional sense, for thousands of years — the earliest recorded evidence goes back roughly 9,000 to 11,000 years, to the beginnings of human civilisation. Nearly every major food crop grown today is the result of the domestication of wild ancestors carried out over this long history.

Classical plant breeding works by crossing (hybridising) pure lines and then selecting the offspring that show the desired traits — higher yield, better nutrition, and greater resistance to disease. With the growth of genetics, molecular biology and tissue culture, plant breeding today increasingly draws on molecular genetic tools as well.

What traits do breeders aim for?

• Increased crop yield and improved quality
• Greater tolerance to environmental stress — salinity, extreme temperature, drought
• Resistance to pathogens — viruses, fungi and bacteria
• Greater tolerance to insect pests

The main steps in breeding a new crop variety

1. Collection of variability — Genetic variability is the starting point of any breeding programme. Breeders collect and preserve the different wild relatives, species and varieties related to a cultivated crop, evaluating each for its useful traits. This complete collection of plants or seeds, carrying all the diverse alleles present for every gene in a crop, is called its germplasm collection.
2. Evaluation and selection of parents — The germplasm is examined to identify plants carrying a desirable combination of characters. These are multiplied, used for hybridisation, and, where possible and useful, developed into pure lines.
3. Cross hybridisation among selected parents — Since the traits a breeder wants are often spread across two different plants (for example, high protein quality in one and disease resistance in another), pollen from the chosen male parent is transferred onto the stigma of the chosen female parent to combine both traits in a hybrid. This step is slow and painstaking, and typically only one cross in a few hundred to a thousand actually produces the desired combination.
4. Selection and testing of superior recombinants — Among the progeny of successful hybrids, breeders select the plants that carry the best combination of characters — plants superior to both parents. These are then self-pollinated over several generations until they become genetically uniform (homozygous), so the desirable characters no longer segregate in later generations.
5. Testing, release and commercialisation — The newly developed lines are evaluated for yield and other agronomic qualities under ideal conditions of fertiliser use, irrigation and crop management in research fields, and then tested further in farmers' fields for at least three growing seasons across the different agro-climatic zones where the crop is normally grown. Performance is always compared against the best locally available variety, used as a check or reference.

India's Green Revolution

Agriculture accounts for roughly 33% of India's GDP and employs close to 62% of its population. After Independence, feeding a rapidly growing population on limited cultivable land was one of the country's biggest challenges. The development of high-yielding varieties of wheat and rice in the mid-1960s, through sustained plant breeding effort, produced a dramatic jump in food production — the period now remembered as the Green Revolution. (Figure 9.3 shows some of the Indian hybrid crop varieties that resulted from this effort — high-yielding maize cobs, a field trial of the semi-dwarf wheat variety Sonalika, and a high-yielding garden pea accession.) …