(a) Describe the history of plant breeding in India. Write the objectives of plant breeding and methods for creation of…

(a) History, objectives and methods of creating variability in plant breeding

History in India. Farmers practised selection of landraces for millennia, and old texts such as the Vrikshayurveda describe seed and plant care. Scientific breeding began with the Department of Agriculture (1871) and the Imperial Agricultural Research Institute, Pusa (1905), where Albert Howard developed rust-resistant Pusa wheats; T.S. Venkataraman and Barber's work at the Sugarcane Breeding Institute, Coimbatore (1912) gave the Co canes, and ICAR was set up in 1929. After independence came the All India Coordinated Crop Improvement Projects (from 1957), hybrid maize (1961), hybrid sorghum (CSH-1, 1964) and pearl millet (HB-1, 1965), the first hybrid cotton (H-4, 1970), and the Green Revolution from 1966–67 with semi-dwarf wheats (Lerma Rojo, Sonalika, Kalyan Sona) and rice (IR8, then Jaya), led by Swaminathan. NBPGR (1976) conserves germplasm; hybrid rice (1994), Bt cotton (2002) and molecular breeding followed.

Objectives: higher yield and stability; resistance to disease, insects and abiotic stress; better quality and nutrition; earliness and adaptation to agro-climatic zones; and suitability for mechanisation and processing.

Creating variability: introduction and germplasm collection; hybridisation (intervarietal, interspecific, intergeneric); mutation breeding with radiation or chemicals (BARC's Trombay groundnuts, Sharbati Sonora wheat); polyploidy and alien gene transfer; somaclonal variation, protoplast fusion and embryo rescue; and recombinant DNA technology (Bt cotton).

(b) Systemic acquired resistance, sources of resistance and advantages of resistance breeding

SAR is an induced, whole-plant, long-lasting and broad-spectrum resistance that follows a local infection or necrosis, discovered by Ross (1961) in tobacco infected by TMV, which later resisted TMV and other pathogens. A mobile signal (methyl salicylate) raises salicylic acid, NPR1 activates defence genes, and pathogenesis-related (PR) proteins (chitinases, glucanases) and cell-wall strengthening follow. Chemical inducers such as benzothiadiazole (BTH) and other elicitors mimic SAR, and it differs from induced systemic resistance, which is jasmonate- and ethylene-dependent.

Sources of disease resistance: the crop's own cultivars and landraces; wild relatives and related species (Oryza longistaminata with Xa21 for bacterial blight; O. nivara for grassy stunt; Aegilops for wheat rusts); induced mutants; other breeding material; and transgenes or engineered genes.

Advantages: the most economic and environment-friendly control; it cuts fungicide and pesticide costs and residues; it needs no extra effort from farmers; it gives durable protection when genes are pyramided or horizontal resistance is used; and it stabilises yields and suits disease problems that chemicals cannot control, as with viral diseases.

(c) Graft incompatibility

Graft incompatibility is failure of a scion and stock to unite and grow normally as one plant, though they are grafted correctly.

Symptoms: poor union or callus and low graft take; early yellowing and defoliation of leaves, sometimes with premature autumn colour; poor shoot growth and dieback; overgrowth or bulging above or below the union; a weak, brittle union that breaks at the joint; stunting, poor fruiting and eventual death, sometimes years after grafting (delayed incompatibility).

Causes: lack of close taxonomic affinity; anatomical mismatch of cambium and vascular tissue; physiological and biochemical differences, such as toxic metabolites (prunasin, a cyanogenic glycoside, in pear on quince) and differences in hormone or phenol levels; and pathogens, especially viruses and phytoplasmas transmitted through the stock.

Examples: pear on quince (pear decline phytoplasma and prunasin); sweet orange on sour orange rootstock with citrus tristeza virus (quick decline); apricot on peach in some combinations; and cherry or plum on certain stocks.