World food production is limited primarily by environmental stresses. It is very difficult to find ‘stress free’ areas where crops may approach their potential yields. Abiotic environmental factors are considered to be the main source (71%) of yield reductions (Boyer, 1982). In past decades, the primary approach for alleviation of environmental stress focused on modification of the environment through irrigation, soil amelioration, fertilizer use, etc. Economic and ecological constraints on environmental amelioration make the approach of genetic improvement of stress resistance a viable alternative for closing the gap between actual and potential crop yields in marginal areas. The world’s cereal production requires a sustained increase of 3% in developing countries to maintain the current levels of nutrition to the year 2000 and beyond.