(a) Give an account of cytoplasmic genetic male sterility and its utilization in plant breeding. Also discuss its limitations…

(a) Cytoplasmic Genetic Male Sterility (CGMS)

CGMS results from mitochondrial genes inducing pollen sterility (S-cytoplasm) unless suppressed by dominant nuclear restorer genes (R_), whereas normal cytoplasm (N) yields fertile plants. Commercial hybrid seed production exploits this through a three-line system: the male-sterile female A-line (S-rr), its isogenic male-fertile maintainer B-line (N-rr), and a male-fertile pollinator R-line (N-RR or S-RR). Crossing A × B multiplies the sterile line, while A × R produces fertile F₁ hybrid seed. In India, CGMS revolutionized hybrid breeding, yielding landmark releases in sorghum (CSH series via CK-60A), pearl millet (HB series via Tift 23A), and rice (the first Indian hybrids of 1994 such as APHR-1 and KRH-1, and later Pusa RH-10 on the WA-cytoplasm line Pusa 6A), alongside transgenic barnase-barstar alternatives in mustard (DMH-11).

However, CGMS faces serious limitations: narrow cytoplasmic uniformity causes extreme genetic vulnerability, exemplified by the 1970 Southern corn leaf blight epidemic in US Texas-cytoplasm maize; scarcity of effective nuclear restorer genes restricts parental choices; sterility expression is often unstable under temperature and humidity fluctuations; the sterile cytoplasm can carry a yield penalty; and seed production needs isolation, synchronised flowering of A and R lines and good outcrossing, which is poor in self-pollinated crops such as rice and wheat. Two-line systems using environment-sensitive genic male sterility (EGMS) avoid the maintainer line.

(b) Distant Hybridization

Distant hybridization involves inter-specific or inter-generic crosses designed to introgress alien genes for biotic and abiotic stress resistance into cultivated crops. Pre- and post-fertilization barriers are overcome through in vitro embryo rescue, bridge crosses, reciprocal pollinations, and chromosome doubling via colchicine. Globally, it yielded the synthetic amphiploid cereal Triticale (Secale cereale × Triticum spp.) and resynthesized Brassica napus. Significant milestones include introgressing grassy stunt virus resistance into cultivated rice (at IRRI) from an Indian accession of the wild ancestor Oryza nivara, The wheat–rye 1BL·1RS translocation spread rust resistance worldwide. In India, nobilisation of sugarcane at the Sugarcane Breeding Institute, Coimbatore (Saccharum officinarum × S. spontaneum) produced the 'Co' canes (e.g., Co 205, and later Co 0238) with vigour, ratooning ability and stress tolerance, and Varalaxmi (1972) was the first commercial interspecific cotton hybrid (Gossypium hirsutum × G. barbadense); wild species have also supplied late blight resistance in potato.

Key limitations encompass cross-incompatibility, F₁ hybrid inviability or sterility, severe linkage drag where deleterious wild alleles persist alongside target traits, and exceptionally long breeding cycles required to restore normal agronomic architecture through recurrent backcrossing.

(c) Seed Production Planning and Organization

Planning begins with estimating demand (indents from states and agencies) and fixing the class and quantity of seed of each variety to produce, working back from certified to foundation to breeder seed needed. The area and season chosen should have a climate favourable for seed set and low disease pressure (for example, seed potato in the hills or in Punjab's low-aphid winter), assured irrigation, and land free of volunteer plants of the same crop in the previous season. Seed growers are organised through contracts or seed villages, with assured source seed, inputs, supervision, buy-back and prices. The programme also plans processing, storage, testing and distribution in time for sowing. Organisation then requires precise spatial and temporal isolation distances to prevent cross-pollination and physical contamination. Mandatory roguing must be executed across vegetative, pre-flowering, flowering, and pre-harvest stages to eliminate off-types, diseased plants, and pollen shedders. Seed multiplication follows a strict generation system: Breeder seed produced by the originating plant breeder is multiplied into Foundation seed by public or private agencies, which is subsequently multiplied into Certified seed distributed to farmers.

This process is institutionally regulated by the Central Seed Committee, State Seed Certification Agencies, and notified seed testing laboratories under the statutory framework of the Seeds Act 1966, the Seed Rules 1968, the New Policy on Seed Development 1988 and the National Seeds Policy 2002.