Plant Breeding Methods
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Direct answer
Conventional plant breeding moves desirable genes into crops through a five-step cycle NCERT fixes as its skeleton: collection of variability (germplasm, including wild relatives), evaluation and selection of parents, cross-hybridisation among the chosen parents, selection and testing of superior recombinants, and testing, release and commercialisation of new cultivars. The strategy delivered India's green-revolution generation of varieties — semi-dwarf wheats Sonalika and Kalyan Sona and rices IR8-derived Jaya and Ratna — plus disease resistance, quality traits, and biofortified lines such as protein-rich Atlas 66 wheat and lysine- and tryptophan-doubled maize. The same selection logic, applied to animals, produced Hisardale sheep in Punjab from Bikaneri and Merino crosses.
What you must remember
- The five steps in order: germplasm collection; evaluation and selection of parents; cross-hybridisation; selection and testing of superior recombinants; testing, release and commercialisation — the numbered-list question of this chapter.
- Why germplasm first: wild relatives and old varieties hold the resistance and quality alleles breeding draws on; they are the library every later step reads from.
- Semi-dwarf revolution: wheat Sonalika and Kalyan Sona (from Norman Borlaug's material), rice IR8 from IRRI in the Philippines, and the Indian-bred Jaya and Ratna — high-yielding under fertiliser and irrigation.
- Sugarcane example: breeding combined the thin north Indian Saccharum barberi with the thicker south Indian Saccharum officinarum for better-yielding, hardy varieties.
- Biofortification targets: Atlas 66 wheat for protein; maize with roughly double the lysine and tryptophan; vegetable varieties bred for higher iron and vitamin content — breeding for nutritional quality, not just yield.
- Mutation breeding: mutations induced to create resistance alleles — mung bean resistant to yellow mosaic virus and Powdery mildew is NCERT's example, with the caveat that desirable mutants are rare.
- Animal parallel: Hisardale, a new sheep breed from Bikaneri ewes crossed with Merino rams, bred in Punjab — cross-breeding combining hardiness with wool quality.
- Time cost: repeated crossing and selection mean a decade or more from cross to cultivar, the reason newer biotechnological shortcuts exist alongside it.
Reason through the steps with one wheat example
Begin with the germplasm: lines carrying rust resistance, including material from Borlaug's programme, entered Indian breeding nurseries in the early 1960s. Breeders evaluated them, chose parents combining resistance with grain type, and cross-hybridised by hand-pollinating emasculated wheat ears. The F2 and later generations segregated for height, resistance and yield, and breeders selected superior recombinants — the offspring that had recombined short stature with the wanted resistances — then tested them across locations and seasons before releasing Sonalika and Kalyan Sona commercially. Every step exists because recombination is uncontrolled: crossing shuffles half a genome's worth of variation each generation, and only patient selection in the field fixes the wanted combination.
Biofortification repeats the same machinery with a different yardstick — not kilograms per hectare but nutrients per meal. Atlas 66 raised wheat's protein; quality-protein maize roughly doubled lysine and tryptophan, the two amino acids conventional maize lacks; breeding programmes have since pushed iron and vitamin-A precursors into staples, a breeding goal India's biofortification initiatives share. The exam asks the trait-crop pairing, so anchor each variety to its nutrient.
Where students lose marks
Variety-crop mixing is the cheapest mark lost: Sonalika and Kalyan Sona are wheats, Jaya and Ratna are rices, IR8 is a rice from IRRI, Atlas 66 a wheat, Hisardale a sheep — a matching set the options shuffle every session. Second, germplasm versus cultivar: germplasm is the collected variability, including wild relatives, not the finished variety. Third, mutation breeding is not transgenesis: induced mutation creates variation inside the species' own genome, with no foreign gene, so do not describe mung bean yellow-mosaic resistance as a GM trait. And keep the five steps in order — evaluation precedes crossing, and release follows selection.
Frequently asked questions
What are the main steps of plant breeding?
Collection of genetic variability, evaluation and selection of parents, cross-hybridisation, selection and testing of superior recombinants, and testing, release and commercialisation of cultivars.
Which semi-dwarf varieties drove the wheat and rice revolutions?
Wheats Sonalika and Kalyan Sona, and rices IR8, Jaya and Ratna — high-yielding semi-dwarfs of the green revolution era.
What is biofortification, with NCERT examples?
Breeding crops for higher nutritional value, as in protein-rich Atlas 66 wheat and maize with about double the lysine and tryptophan.
What is Hisardale?
A sheep breed developed in Punjab by crossing Bikaneri ewes with Merino rams, an animal-breeding parallel to crop improvement.
Why is germplasm collection the first step?
Germplasm, including wild relatives and old varieties, is the reservoir of alleles for resistance and quality that every subsequent selection draws upon.