Classical Agriculture and Animal Husbandry

All products of agriculture and animal husbandry of 10,000 years are genetically modified and so they are Genetically Modified Organisms (GMOs) and Living Modified Organisms (LMOs).

Wild plants and animals evolved undergoing genetic modification basing on natural variation existing at a given time and Natural Selection acting upon it. On the other hand, cultivated plants and domesticated animals came into being by conscious human effort, initially from farmers and later on from professional scientists.

Human or artificial selection:
The guiding force in the development of cultivated plants and domesticated animals is human or artificial selection, the process of intentional or unintentional genetic modification of a species through human actions favouring the breeding of certain traits over others.

Experimental induction of variation:
Till the beginning of the last century, human selection was confined to taking advantage of the genetic variation that naturally existed in the populations, from which beneficial traits were chosen. Subsequently, several experimental procedures were devised to induce variation, providing for a larger pool of beneficial traits.

a) Induced mutations: In nature beneficial gene mutations can only be detected randomly and sporadically and there was never an adequate pool of mutants to select from. In course of time techniques have been developed to induce mutations. Mutations may be induced by physical means such as exposure to ultraviolet, alpha, beta, gamma, and X- rays, or by extreme changes in temperature, and by chemical mutagens such as nitrous acid, nitrogen mustard, and chemical substitutes for segments of nucleotide sequences of genes. These methods provided an enormous pool of mutants affording a very wide choice for beneficial traits.

Physical and chemical mutagens also provided a fund of information to understand gene expression and modification. At the same they threw up monstrosities that warned of the risks involved in the method, and the need to choose mutants with caution.

b) Experimental hybridization: Natural hybrids among the cultivated plants and domesticated animals were used initially but their utility was limited on account of poor understanding of their nature and difficulties in identifying the few useful traits, in a plethora of others.

In 1715, Thomas Fairchild produced the first recorded man made hybrid of two garden plants—the carnation (Dianthus caryophyllatus) and the Sweet William (Dianthus barbatus). In 1780, Josef Kolreuter successfully crossed tobacco plants. Gregor Mendel discovered the principles of inheritance through hybridizing pea varieties in 1865 and this work formed the foundation for the science of genetics. Between 1870 and 1890, plant breeders produced hundreds of cotton hybrids with improved qualities. The area of experimental hybridization emerged in due course, when methods were devised to overcome most barriers to hybridization by artificial fertilization by hand pollination. Animal husbandry expanded by developing artificial insemination. Agricultural scientists took full advantage of hybrid vigour or heterosis and produced superior varieties. The only impediment remained was the presence of genetic or physiological barriers and/or absence of genetic relationship.

c) Induced polyploids: Induction of polyploidy became crucial not just for the advantages of some polyploids, but to restore fertility in hybrids, aneuploids and chromosomal aberrants, by producing amphidiploids. Among the several methods developed to induce polyploidy, the use of colchicine, a plant alkaloid used to treat gout, proved to be the most versatile.

d) Tissue culture: Tissue culture is the general term for the technique of culturing cells, tissues, organs or whole organisms, in the laboratory. Since the 1950s elaborate protocols have been developed to grow almost anything thing in the labs, leading to cloning of plants and animals.

Tissue culture is versatile technique, on account of totipotency, which is the ability of a single cell, to divide and produce all the differentiated cells and tissues of an organism, because all the cells of an organism contain the complete genetic information needed to develop the whole organism.

Starting from small bits of tissues from the growing points of plants (explants), whole plants can be developed. This method, called micropropagation, is now extensively used to produce plantlets on a commercial scale for cultivation, where raising plants from the seed is fraught with difficulties.

When embryos of hybrids fail to develop, the immature embryos can be excised and grown on artificial media to complete their development, and to raise plants from them, by a technique called embryo rescue.

Taking advantage of such developments in different areas of biology, classical agricultural scientists devised methods to introduce variation, to take advantage of it and to over come difficulties in developing improved varieties of crops and domesticated animals, long before the advent of modern agricultural biotechnology.

November 21, 2005