Euphytico 57: 13H40, 1991. 0 1991 Kluwer Academic Publishers. Printed in the Netherlands Variation in response to infection with Erysiphe graminis hordei and Pucciniahordei in some wild barley populations in a centre of diversity S. Jana’ & E. Nevo’ l Department of Crop Science and Plant Ecology, University of Saskatchewan, Saskatoon, S7N OWO, Canada; 2 institute of Evolution, University of Haifa, Mount Carmel, Haifa 31 999, Israel Received 2 March 1991; accepted I& September1991 Key words: germplasm, in situ preservation, wild barley, Hordeum spontaneum, powdery mildew, leaf rust, centre of diversity The Near East Fertile Crescentextending from Iran to Israel is the centre of origin of cultivated barley and a region of great genetic diversity in wild barley, Hordeum spontaneum C. Koch (syn. H. vulgare ssp. spontaneum (C. Koch Thell)). Wild barley accessions collected from different parts of this region were evaluated for their reactions to infection with three isolates of Erysiphegruminis hordei and two of Pucciniu hordei. One culture of each pathogen was isolated in Israel and the others, either in Japan or the United States. Out of a total of 330 wild barley accessions collected from 14 sitesin Iran, Turkey and Syria, only 18.8% were resistant to the Israeli culture, and 14.8% were resistant to a composite of the Japanese and American cultures of E. graminis hordei. Out of 105accessions collectedfrom sixsitesin Iran and Turkey, none was found to be resistantto the Israeli culture and 34.3% were resistantto the American culture of P. hordei. Considerable variation was observed both within and among sitesfor reactions to infection with different cultures of each of the two pathogens. The results of this study were compared with those of an earlier study involving wild barley accessions from Israel to illustrate the relative importance of different subregionsin the Near East Fertile Crescentassources of new genesfor resistance to E. gruminis hordei and P. hordei. Implications of these studies for in situ conservation of genetic diversity in wild barley are discussed. Introduction Wild barley, Hordeum spontaneum C. Koch (syn. H. vulgare L. ssp.spontaneum (C. Koch) Thell.), the immediate evolutionay progenitor of cultivated barley, H. vulgare L., is a predominantly self-ferti- lizing diploid (2n = 14) annual which colonizes primary and secondary habitats from eastern Af- ganistan to the Atlantic North Africa, with high concentrations along the Near East Fertile Cres- cent (Harlan & Zohary, 1966). In the latter region, the wild species usuallyoccupies areasbelow 1,500 metres elevation, where a wide variety of ecolog- ical and morphological forms are found (Zohary, 1969; Zohary & Hopf, 1988). Populations of wild barley, growing in their natural habitats in some parts of the Near East Fertile Crescent, have been found to be genetically highly polymorphic for large number of isozyme markers, and the level of polymorphism varied greatly among sites (Brown et al., 1978a,1978b; Jana & Pietrzak, 1988; Nevo et al., 1986a,1986b,1986~; Nevo et al., 1979a, 1979b). Worldwide, both powdery mildew, Erysiphe gruminis DC. Ex Merat. f. sp. hordei em. Marchal,