Euphytica 121: 81–86, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 81 Tolerance to paraquat is correlated with the traits associated with water stress tolerance in segregating F 2 populations of barley and wheat Ahu Altinkut 1 , Kemal Kazan 2 , Zeliha Ipekci 1 & Nermin Gozukirmizi 1,3∗ 1 Tubitak, Marmara Research Center, Research Institute for Genetic Engineering and Biotechnology, P.O. Box 21, 41470, Gebze-Kocaeli, Turkey; 2 Cooperative Research Centre for Tropical Plant Pathology, The University of Queensland, John Hines Building, St. Lucia, Brisbane, Queensland 4072, Australia; 3 The University of Istanbul, Faculty of Science, Department of Biology, Vezneciler-Istanbul, Turkey; ( ∗ author for correspondence) Received 26 October 1999; accepted 20 October 2000 Key words: drought tolerance, Hordeum vulgare, Triticum aestivum, paraquat tolerance Summary To identify scorable marker traits that can be used in cereal breeding programs for selecting drought tolerant individuals, we investigated the correlation among the drought-associated traits in two F 2 populations derived from the crosses made between drought tolerant and sensitive barley and wheat parental genotypes. The parental genotypes of these crosses also differed by at least three other traits – paraquat tolerance, leaf size, and the relative water content. These three traits were scored in two F 2 populations of 80 individuals for each barley and wheat cross. Analysis of results indicated that the enhanced tolerance to paraquat was correlated with reduced leaf size and increased relative water content, two traits associated with water stress phenotypes of the drought tolerant barley and wheat parents. Our results suggested that the selection based on paraquat tolerance is technically less demanding and thus useful for rapid screening of individuals for enhanced drought tolerance in segregating populations. Abbreviations: PQ – Paraquat; RWC – Relative Water Content Introduction One of the most serious problems encountered in semi-arid and arid climatic regions is lack of water to obtain sufficient product from crop plants. Drought is a multi-dimensional stress, which causes various physiological and biochemical effects on plants. Such effects may include reduction in cell division and thus retardation of cellular growth, decrease in pho- tosynthesis, closure of stomata and changes in the amount of chlorophyll (Turner, 1986; Tanaka et al., 1990; Irigoyen et al., 1992; Smirnoff, 1993; Bohnert & Jensen, 1996; Jamaux et al., 1997; Tabaeizadeh, 1998). The other cellular alterations such as decreased protein content, increased ribonuclease activity, pro- tein hydrolysis, hydrogen peroxide concentration and dissociation of polyribosomes are also known to oc- cur in plants exposed to water stress (Levitt, 1980; Mukherjee & Choudhuri, 1983). Evidence from different lines of research suggests that water deficit also causes oxidative stress in plants (Moran et al., 1994; Foyer et al., 1994). Limitation of photosynthesis and exposure to high irridance dur- ing water stress can increase the rate of active oxygen formation in chloroplasts or hinder the activity of an- tioxidant defenses (Smirnoff & Colombe, 1988). This effect of water stress on the physiology of plants is very similar to the stress caused by PQ (a bypridlium herbicide), which leads to the production of highly toxic free radicals generated by reaction of molecu- lar oxygen with PQ radicals formed in the chloroplast during photosynthesis (Dodge, 1971). Therefore, a close correlation is expected between the plant’s tol- erance to stresses imposed by water and PQ. It is also possible that drought tolerant plants can be selected based on their response to PQ in segregating breeding populations if an association between drought/water stress associated traits and PQ tolerance could be