Recent advances in breeding barley for drought and saline stress tolerance

Abstract

Barley is the most tolerance cereal crop for drought and salinity and is an ideal model crop for genetic study of drought and salinity tolerance because of its early maturity, diploid and self-pollination. Selection for drought tolerance in convention breeding programs has achieved significant progress to improve yield and yield stability under drought through direct selection or indirect selection for early vigour, coleoptile length or "stay green". A large number of Quantitative Trait Loci (QTL) were mapped for drought and salinity tolerance related traits, including physiological biochemical traits such as osmotic adjustment capacity, proline content, stomatal conductance, water-soluble carbohydrates, relative water content, leaf turgor, ABA content, transpiration efficiency, water use efficiency and carbon isotope discrimination; and developmental/morphological traits such as height, leaf emergence, leaf area index, tiller development, flowering time, maturity rate and root characteristics. QTLs for yield and yield components were also identified under drought. Extensive research has been devoted to the characterization of genes induced or up-regulated by drought or salinity. Numerous candidate genes were identified to associate with tolerance to drought or salinity and some of the candidate genes co-located with the QTLs for drought tolerance. Wild barley (Hordeum spontaneum) was demonstrated as a key genetic resource for drought and salinity tolerance. QTLs from the wild barley increased yield by 12-22% under drought. New germplasm and molecular tools make it possible to develop better barley variety faster for drought or salinity tolerance, but challenges still remain due to complexity of drought and salinity tolerance. Barley (Hordeum vulgare L.) is the fourth largest cereal crop in the world with annual production over 140 million tonnes. It has been used as a staple food for humans, feed for animals, and a key ingredient in beer and whiskey production. Barley has a wider ecological range than any other cereals and is widespread in temperate, subtropical and artic areas, from sea level to heights of more than 4,500 m in the Andes and Himalayas (Bothmer et al., 1995). Barley can be grown on soils unsuitable for wheat, and at altitudes unsuitable for wheat or oats. Because of its salt and drought tolerance, barley thrives in nearly every corner of the earth including extremely dry areas near deserts. Barley is a short-season, early maturing, diploid and self-pollinating crop, thus it is also an ideal model plant for genetic study of drought and salinity tolerance. Several papers have summarized research on barley abiotic stress tolerance including drought and salinity tolerance (Cattivelli et al., 2002; Stanca et al., 2003). In this chapter, we will review recently progress on molecular breeding for saline and drought tolerance in barley © 2007 Springer.