(a) What do you mean by gene pool concept and genetic erosion ? Classify the gene pool of a crop. 10 (b) Describe the advantages…

(a) Gene pool, genetic erosion and classification of a crop gene pool

The gene pool is the sum of all genes and alleles in a crop species and its relatives, the raw material for breeding. Genetic erosion is the loss of this genetic diversity, caused by replacement of landraces with a few uniform high-yielding varieties, monocropping, habitat destruction, urbanisation and climate change. It narrows the genetic base and reduces adaptability to new pests and stresses; the loss of many local rice landraces after the Green Revolution is a well-known example.

Harlan and de Wet classified the gene pool by crossability: the primary pool (GP-1) comprises cultivated forms, landraces and wild forms of the same biological species that cross freely; the secondary pool (GP-2) comprises related species that cross with difficulty and give partly sterile hybrids; and the tertiary pool (GP-3) comprises distant relatives, usable only through embryo rescue, bridge crosses or genetic engineering. Conservation is through gene banks such as NBPGR in New Delhi.

(b) Mass, simple recurrent and clonal selection: advantages and disadvantages

Mass selection chooses superior plants by phenotype and bulks their seed, mainly in cross-pollinated crops such as maize. Advantages: simple, quick, cheap and keeps variability. Disadvantages: selection is on phenotype alone with no progeny testing, so environmental effects mislead; pollen parent is uncontrolled, and gain is slow for low-heritability traits.

Simple recurrent selection selects superior plants, inter-mates them and repeats the cycle, raising the frequency of favourable alleles. Advantages: progressive gain through additive gene action and variation retained for further cycles. Disadvantages: several long cycles, little help for traits dominated by non-additive action and a risk of inbreeding with few parents.

Clonal selection selects superior clones in vegetatively propagated crops such as potato and sugarcane. Advantages: it fixes the whole genotype, including dominance and epistasis, immediately, and the variety is uniform. Disadvantages: it depends on existing variability, the genetic base is narrow, and virus and disease accumulate through successive vegetative generations.

(c) Importance of somatic hybridisation in agriculture

Somatic hybridisation fuses protoplasts of two different cells, using polyethylene glycol or electrofusion, and regenerates plants. It overcomes sexual incompatibility between distant species and combines whole genomes, as in the potato-tomato 'pomato'.

Importance: transfer of disease resistance, such as potato leafroll virus resistance from wild Solanum brevidens to potato; creation of cybrids that carry the nucleus of one parent and the cytoplasm of the other, used to introduce cytoplasmic male sterility, for instance into Brassica napus for hybrid seed production; transfer of cytoplasmic traits, new allopolyploids and tolerance to stresses. Its limits are poor regeneration of fusion products, chromosome loss, sterility, and the technical difficulty of protoplast culture, so it complements rather than replaces conventional breeding.

(d) Intellectual Property Rights (IPR) in agriculture

IPR in agriculture covers plant variety protection, patents and geographical indications. TRIPS Article 27.3(b) requires plant variety protection by patents or an effective sui generis system; India chose sui generis, enacting the Protection of Plant Varieties and Farmers' Rights (PPV&FR) Act, 2001, and the Patents Act excludes plants and seeds. The Act gives breeders exclusive rights and registers extant varieties, but also protects farmers: they may save, use, sow, exchange and sell farm-saved seed (other than branded seed), and have rights to benefit sharing and recognition as conservers.

The sensitivity arises from the conflict between breeder incentives and farmers' seed sovereignty, and from biopiracy, as in the neem and basmati patent disputes. Conclusion: strong protection is needed to encourage private research, but must be balanced with safeguards for small farmers' access to seed and germplasm and benefit sharing.

(e) Short notes

(i) Asexual reproduction is propagation without fusion of gametes, either vegetatively (tubers, cuttings, runners, bulbs, grafting) or by apomixis (seed without fertilisation). It preserves a superior genotype exactly, as in banana, potato and sugarcane.

(ii) Progeny test evaluates a parent's breeding value from the performance of its offspring (half-sib or full-sib families). It is used in recurrent selection and in animal breeding.

(iii) Seed bank is an ex-situ gene bank storing seeds at low temperature and humidity to conserve germplasm, for example NBPGR's National Gene Bank, New Delhi, and the Svalbard Global Seed Vault.

(iv) Genetically modified crop carries a transgene introduced by genetic engineering, for example Bt cotton, India's only commercially approved GM crop (2002). GM mustard (DMH-11) was cleared for environmental release by GEAC in 2022, and the Supreme Court in July 2024 delivered a split verdict and asked the Centre to frame a national GM policy. Biosafety is regulated by GEAC.