L. Krishnamurthy, M. Zaman-Allah, R. Purushothaman,

M. Irshad Ahmed and V. Vadez

International Crops Research Institute for the Semi-Arid Tropics (ICRISAT),

Patancheru 502 324, Andhra Pradesh

India

1. Introduction

1.1 Prevalence of abiotic stresses in SAT agriculture

The semi-arid tropics (SAT) include parts of 48 countries in the developing world: in most of India, locations in south east Asia, a swathe across sub-Saharan Africa, much of southern and eastern Africa, and a few locations in Latin America (Fig 1). Semi-arid tropical regions are characterized by unpredictable weather, long dry seasons, inconsistent rainfall, and soils that are poor in nutrients. Sorghum, millet, cowpea, chickpea, pigeonpea and groundnut are the vital crops that feed the poor people living in the SAT.

Environmental stresses represent the most limiting factors for agricultural productivity. Apart from biotic stresses caused by plant pathogens, there are a number of abiotic stresses such as extremes temperatures, drought, salinity and radiation which all have detrimental effects on plant growth and yield, especially when several occur together (Mittler 2006).

salinization, as a result of sparse and seasonal rainfall and mismanagement of the natural resource base for agriculture (Evans, 1998). Expansion of irrigation does not seem feasible in many countries in Asia, the Middle East, and North Africa, where most of the available and easily accessible water resources have been already utilized. Furthermore, irrigated soils are affected by salinity with significant subsequent yield losses. Desertification may be aggravated by both extensive farming due to demographic pressure and the regional climatic changes. Hence, there is a need for the breeding programs to assign high priority for the development of crops with tolerance to both drought and salinity stress. The genetically complex control of these stresses in the plant genome may be facilitated through the manipulation of specific genes governing the component characteristics needed to achieve tolerance to salt or drought in plant crops.