Breeding for Drought Resistance

Drought may be defined as a period during which soil or plant water deficiencies affect growth and yield. Such moisture deficiencies may occur through a reduction in the moisture supply or through an increase in demand. Drought is a recurrent problem of rainfed agriculture throughout the world. Marginal and submarginal lands in semiarid and arid regions, characteristically depending on rains for their cultivation, are particularly prone to such water deficit problems. The intensity and duration of droughts faced by these lands may, however, vary considerably over time and between climatic zones. These so-called drought-prone zones, including desert regions, bestowed with low precipitation, high ambient temperature, and drought-induced secondary stresses, are commonly known for dismally poor agricultural productivity. The rainfed zones subject to droughts are vast with global occurrence. Arid and semiarid regions, under the serious threat of drought, occupy almost 6 billion hectares of land in more than 100 countries. For instance, out of 1,474 million hectares (Mha) of cultivated lands worldwide, rainfed lands occupy 1,247 Mha. These rainfed lands are found predominantly in Asia (309 Mha), followed by North America (248 Mha), the former Soviet Union (233 Mha), Africa (174 Mha), South America (133 Mha), Europe (123 Mha), and Australia (47 Mha) (Ghassemi et al., 1995). Thus, 84 percent of the world’s cultivated lands are rainfed and this has major implications for the global economy and trade. The occurrence of drought depends on soil, climate, social factors, and cropping intensity; and severity and time of occurrence may not easily be predicted. Throughout the world, however, drought is considered to be the main agricultural menace limiting the successful realization of land potential and consequently reducing crop productivity.