Using genetic diversity for disease resistance in agricultural production

The three main germplasm resource bases used for genetic diversity in disea se resistance are commercial varieties, landraces and wild ancestral specie s. Cultivar mixtures with landraces have traditionally been used by subsist ence farmers to keep disease epidemics at low levels. These subsistence far mers Live mainly in developing countries and produce up to 20% of the world 's food. Landraces have been a valuable source of disease resistance to the m because of their already high adaptations in appropriate agronomic backgr ounds. Mixtures with improved varieties are now being advocated as an alter native strategy for disease control in many crops. Wild germplasm are also being used to transfer new and valuable genes of disease resistance to cult ivated crops. Continuous efforts are being directed at broadening the genet ic base of crops by a search for sources of disease resistance, which remai n the most practical and environmentally sound means for the control of mos t major diseases in agricultural crops.