The development and application of molecular markers for abiotic stress tolerance in barley

This article represents some current thinking and objectives in the use of molecular markers to abiotic stress tolerance. Barley has been chosen for s tudy as it is an important crop species, as well as a model for genetic and physiological studies. It is an important crop and, because of its well-st udied genetics and physiology, is an excellent candidate in which to devise more efficient breeding methods. Abiotic stress work on cultivated gene po ols of small grain cereals frequently shows that adaptive and developmental genes are strongly associated with responses. Developmental genes have str ong pleiotropic effects on a number of performance traits, not just abiotic stresses. One concern is that much of the genetic variation for improving abiotic stress tolerance has been lost during domestication, selection and modern breeding, leaving pleiotropic effects of the selected genes for deve lopment and adaptation. Such genes are critical in matching cultivars to th eir target agronomic environment, and since there is little leverage in cha nging these, other sources of variation may be required. In barley, and man y other crops, greater variation to abiotic stresses exists in primitive la ndraces and related wild species gene pools. Wild barley, Hordeum spontaneu m C. Koch is the progenitor of cultivated barley, Hordeum vulgare L. and is easily hybridized to H, vulgare. Genetic fingerprinting of H. spontaneum h as revealed genetic marker associations with site-of-origin ecogeographic f actors and also experimentally imposed stresses. Genotypes and collection s ites have been identified which show the desired variation for particular s tresses. Doubled haploid and other segregating populations, including landr ace derivatives have been used to map genetically the loci involved. These data can be used in molecular breeding approaches to improve the drought to lerance of barley. One strategy involves screening for genetic markers and physiological traits for drought tolerance, and the associated problem of d rought relief-induced mildew susceptibility in naturally droughted fields o f North Africa.