Plant Breeding

Mass selection picks visually superior plants from a mixed population and bulks their seeds — it does not test individual progeny, so gains are limited by the genetic heterogeneity of the selected group. Pure line selection goes further: selected plants are self-fertilised for several generations to produce homozygous lines, each progeny-tested separately, and the best homozygous line is released as a variety. Pure line selection is used in self-pollinated crops like wheat and rice.

Heterosis (hybrid vigour) is the superiority of an F1 hybrid over its parents. It is measured as: Mid-parent heterosis = (F1 − MP) / MP × 100 (MP = mean of two parents), or Better-parent heterosis (heterobeltiosis) = (F1 − BP) / BP × 100. Commercial heterosis compares F1 to the best available variety. Heterosis is highest for fitness traits (yield, survival) and lowest for quality traits (oil content, protein). It is exploited in hybrid rice, maize, bajra, and cotton.

Colchicine is an alkaloid extracted from Colchicum autumnale (autumn crocus). It inhibits spindle fibre formation during cell division by binding to tubulin, preventing chromosome separation — resulting in cells with doubled chromosome numbers (polyploidy). Applied to growing shoot tips as 0.1–0.5% aqueous solution or lanolin paste. Used to create tetraploids from diploids — e.g., tetraploid watermelon (used to produce triploid seedless varieties), amphidiploid wheat species.

Backcross breeding transfers a single desirable gene (usually disease resistance) from a donor parent into an established high-yielding variety (recurrent parent) without disrupting its other traits. The donor × recurrent cross is repeatedly backcrossed to the recurrent parent for 5–6 generations, selecting for the donor gene in each generation. After 6 backcrosses, ~98.4% of the genome is recurrent parent. Used to introduce resistance: HYVs of wheat, rice, etc.

Mutation breeding uses physical mutagens (X-rays, gamma rays — Co-60, neutrons) or chemical mutagens (EMS — ethyl methane sulphonate, colchicine, sodium azide) to artificially induce mutations in plant material and then screen for useful variants. Gamma rays from Co-60 are the most commonly used mutagen. Famous mutant varieties: NP-836 (Pusa Lerma) wheat, Sharbati Sonora wheat (gamma ray mutant), Atomita-2 rice. India has developed 350+ mutant crop varieties — second highest globally after China.

Variety release in India follows a multi-stage process: (1) Breeder develops the variety and conducts preliminary trials; (2) Coordinated trials through ICAR (All India Coordinated Research Projects — AICRPs) for 3–4 seasons across locations; (3) Central/State Variety Release Committee evaluates performance; (4) Released varieties are notified under the Seeds Act 1966 in the Gazette of India; (5) Registered under PPVFRA (Protection of Plant Varieties and Farmers' Rights Authority, 2001) for IP protection.