Biotechnology and methods of conservation of plant genetic resources

Journal Article

Development

The loss of biological diversity is of major environmental concern at the present time. Whether this relates to the destruction of the tropical rain forests, for instance, or the threat which faces natural ecosystems as climates change due to global warming (Jackson et al., 1990), it is important that in order to survive and continue to evolve, plant and animal species must contain an ample reservoir of genetic diversity. One aspect of this process is the continuing loss of genetic diversity in the crops upon which world agriculture is based. Scientists throughout the world are rightly engaged in developing better and higher yielding cultivars of crop plants to be used on increasingly larger scales. But this involves the replacement of the generally variable, lower yielding, locally adapted strains grown in traditional farming systems, by the products of modern agriculture. Nowadays every major crop has a relatively narrow genetic base, aild so under such situations, diversity in farming systems is replaced by genetic uniformity. However, in order to be able to respond to the various stresses that threaten modern agriculture, plant breeders are dependent upon the availability of a pool of diverse genetic material. The significance of genetic uniformity can be highlighted by several crop exampies, one of historical importance and two others of more recent times. The history of the potato in Europe illustrates the necessity for utilizing genetic resources to broaden the genetic base of crop plants. The narrow genetic base of the potato crop was recognised during the last century following the devastating epidemics of late blight disease, caused by Phytophthora infestans, in the 1840s in Ireland Masswe destruction of the corn crop came about m the United States in 1970 with the southern corn leaf blight epidemic (caused by the fungus Helmmthosportum maydls ). Modern plant breeding had led to the use of a cytoplasrmc gene which conferred suscepnbllity to a particular race of this fungal pathogen. A more recent, but less publicised case of genetic vulnerablhty was caused not by plant disease, but by cold weather. By 1972 tn the Soviet Union the wheat variety 'Bezostaja' was grown on almost 15 million hectares. It had been moved beyond its ongmal area of cultivation into the Ukraine during a period of relatively mild winters. Then in 1972 a very severe winter occurred, causing losses of millions of tons of winter wheat (Fischbeck, 1981). In relation to this example, we can ask whether global warrmng will lead to similar crop losses in the future (Jackson and Ford-Lloyd, 1990). Plant genetic resources (germplasm) is a term used to describe the total genetic diversity of cultivated species and their wild relatives, much of which may be of value to breeders. Although commercial and obsolete varieties, breeders' lines and induced or natural mutations may be included under this term, it is much more usual to describe plant genetic resources as landraces or primitive forms, weed races which are closely related to the cultivated species, and related wild species. Landraces are populations of crops, often collected from remote areas, where the new, highly bred cultlvars have not been introduced. They are highly diverse genetically, and have often been grown as mixtures of species, as well as diverse populations of one species. Such materials are closely allied genetically to modern varieties and are extremely important genetic resources, and as such have received top priority for conservation.