Plant Breeding

Plant breeding is the deliberate, purposeful manipulation of the heredity of crop plants, aimed at producing new varieties that are genuinely superior to the varieties already in cultivation. Because it applies scientific principles to a living, evolving system, plant breeding sits at the intersection of several disciplines — genetics (to understand and control inheritance), taxonomy (to correctly identify and use related wild and cultivated species), physiology and pathology (to understand what makes a plant productive or vulnerable), agriculture (to actually grow and evaluate the new varieties) and, increasingly, rDNA technology (to engineer traits directly). It is fair to call plant breeding both an art and a science: an art, because recognising a genuinely promising plant among thousands of others is still partly a matter of trained judgement, and a science, because every step from crossing to selection is grounded in genetic principles.

The overarching aim of any breeding programme is to produce a new variety that outperforms the existing type across every character that matters for that crop — but because different crops are grown for different purposes (a cereal is bred mainly for grain yield, a fodder crop mainly for biomass, a vegetable mainly for taste and shelf life), the specific objectives of a breeding programme vary from plant to plant. Even so, certain objectives recur across almost every crop: higher yield, better quality (nutritional or otherwise), resistance to pathogens, tolerance of insect pests, tolerance of environmental stresses (drought, salinity, extreme temperature) and a life-cycle span appropriate to the region's growing season.

The Green Revolution. The Green Revolution was the outcome of a chain of scientific breakthroughs and development work that fought hunger by raising food production: seed of superior quality, the use of chemical pesticides and fertilizers, multiple-cropping systems, modern farm machinery and proper irrigation together made it possible to develop and grow high-yielding, disease-resistant varieties of wheat, rice, maize and other crops.

Plant breeding is not a modern invention. Farmers have been selecting and improving crop plants for roughly 10,000 years, and virtually every crop grown today is itself the end product of millennia of unconscious and, later, deliberate domestication and acclimatization — long before Mendel's laws or the science of genetics existed to explain why the process worked. What has changed in the last century is the range of deliberate methods available: introduction of superior varieties from elsewhere, selection within existing populations, hybridization (crossing different parents), mutation breeding (using induced or natural mutations), polyploidy breeding (manipulating chromosome number), molecular/marker-assisted plant breeding, tissue culture and rDNA (genetic engineering) technology. This chapter develops hybridization and mutation breeding in detail, since these two methods underpin the Green Revolution and most of the named Indian crop varieties described below.