Remains of barley (Hordeum vulgare) grains found at archaeological sites in the Fertile Crescent indicate that about 10,000 years ago the crop was domesticated there from its wild relative Hordeum spontaneum. The domestication history of barley is revisited based on the assumptions that DNA markers effectively measure genetic distances and that wild populations are genetically different and they have not undergone significant change since domestication. The monophyletic nature of barley domestication is demonstrated based on allelic frequencies at 400 AFLP polymorphic loci studied in 317 wild and 57 cultivated lines. The wild populations from Israel-Jordan are molecularly more similar than are any others to the cultivated gene pool. The results provided support for the hypothesis that the Israel-Jordan area is the region in which barley was brought into culture. Moreover, the diagnostic allele I of the homeobox gene BKn-3, rarely but almost exclusively found in Israel H. spontaneum, is pervasive in western landraces and modern cultivated varieties. In landraces from the Himalayas and India, the BKn-3 allele IIIa prevails, indicating that an allelic substitution has taken place during the migration of barley from the Near East to South Asia. Thus, the Himalayas can be considered a region of domesticated barley diversification.

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On the Origin and Domestication History of Barley (Hordeum vulgare)

The development of new barleys tolerant of abiotic and biotic stresses is an essential part of the continued improvement of the crop. The domestication of Introduction barley, as in many crops, resulted in a marked trunca- The improvement of abiotic stress tolerance in the barley tion of the genetical variation present in wild popula- crop (Robinson et al., 2000) depends on understanding tions. This process is significant to agronomists and the range of genetic variation possessed by cultivated scientists because a lack of allelic variation will pre- barley (Hordeum vulgare subsp. vulgare L.) and wild vent the development of adapted cultivars and hinder barley (H. vulgare subsp. spontaneum C. Koch.). In turn, the investigation of the genetic mechanisms under- the rate of progress depends on the occurrence of genetic lying performance. Wild barley would be a useful variation desirable for crop development and the availabsource of new genetic variation for abiotic stress toler- ility of precise methods of gene transfer and selection. ance if surveys identify appropriate genetic variation The development of dense chromosome maps, based and the development of marker-assisted selection on molecular markers, has permitted the detection of allows efficient manipulation in cultivar development. quantitative trait loci (QTL) (Hayes et al., 1997; Thomas There are many wild barley collections from all areas et al., 1998) for a range of characters in cultivated barley. of its natural distribution, but the largest are derived This gives potential for the study of genetic mechanisms from the Mediterranean region. The results of a range underlying field performance and reveals the need for of assays designed to explore abiotic stress tolerance new genetic variation. Even in the relatively benign envirin barley are reported in this paper. The assays onments experienced in Scotland, where spring barley included; sodium chloride uptake in wild barley and a crops have higher yield potential than in southern mapping population, effects for d13C and plant dry England ( Ellis and Kirby, 1980), periodic drought can weight in wheat aneuploids, effects of photoperiod and depress yield (Russell and Ellis, 1988). While such cycles vernalization in wild barley, and measurements of root

Wild barley: a source of genes for crop improvement in the 21st century?

Randomly amplified polymorphic DNA (RAPD) markers were used to analyse genetic diversity within and between Hordeum spontaneum populations sampled from Israel. Nei's index of genetic differentiation was used to partition diversity into within and between population components. Fifty-seven per cent of the variation detected was partitioned within 10 H. spontaneum populations. Using principal component and multiple regression analysis, part of the variation detected between populations was seen to be associated with certain ecogeographical factors. Fifty-eight per cent of the distribution of the phenotypic frequencies of three RAPD phenotypes detected using a single primer in 20 H. spontaneum populations could be accounted for by four ecogeographical variables, suggesting adaptive variation at certain RAPD loci.

Detection and analysis of genetic variation in Hordeum spontaneum populations from Israel using RAPD markers

Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.

Detection of quantitative trait loci for agronomic, yield, grain and disease characters in spring barley (Hordeum vulgare L.).

Thirty-nine genotypes of Hordeum spontaneum were selected from three geographically separated areas (southwestern, northern, and southeastern) of the Fertile Crescent. The lines were subject to AFLP (amplified fragment length polymorphism) analysis from which a similarity matrix was produced. A dendrogram of the data showed, with two exceptions, that the genotypes grouped together according to area of origin. This was confirmed by principal coordinate analysis in which the first principal coordinate separated the genotypes of the southwestern area from the other two areas, which in turn could be separated by the second principal coordinate. While genotypes from the same site of origin can exhibit very similar AFLP profiles, sharp genetic differences were detected between genotypes separated by relatively short distances. Thirty of the 39 genotypes were subjected to hydroculture salt tolerance tests. These were analysed for shoot Na+ content and carbon isotope composition (δ13C) after 4 weeks of treatment ...

AFLP variation in wild barley (Hordeum spontaneum C. Koch) with reference to salt tolerance and associated ecogeography

Grain isozyme and ribosomal DNA (rDNA) variability was examined in Hordeum spontaneum populations sampled from 27 geographical sites in Israel. Considerable phenotypic variability was observed with variants of ADH1, EST3, EST10, BMY1 and WSP detected, which are not available in the H. vulgare gene pool. Seven new rDNA phenotypes were detected in the H. spontaneum populations. Shannon's index of diversity was used to partition the total phenotypic variation into between and within population components. Most of the variation occurred between H. spontaneum populations. The distribution of both grain isozyme and rDNA phenotypes was non-random and correlated with a range of ecogeographical factors. In particular, the G phenotype of BMY1 was restricted to the Negev Desert and Dead Sea regions of Israel. Over 78% of the variation in the frequency of this particular phenotype could be explained by the number of rainy days per year and mean temperature in January. This suggests that variation at this locus or at loci linked to it may be of adaptive significance and of value in the introgression of genes controlling abiotic stress tolerance from H. spontaneum into the H. vulgare gene pool.

Grain isozyme and ribosomal DNA variability in Hordeum spontaneum populations from Israel.

Water-soluble proteins (WSP-2 and WSP-3) and β-amylase (β-AMY-1) were extracted from mature endosperms of 44 spring and 39 winter barley genotypes. The protein and enzyme isoforms were separated in isoelectric focusing gels with a pH gradient of 4-6.5. The Wsp-3 and β-Amy-1 loci were located to chromosomes 4H using the wheat/barley chromosome addition lines. Segregation analysis of F2 and doubled haploid populations showed Wsp-2 and β-Amy-1 to be tightly linked, with a map distance of 11 cMorgans. Isoforms of WSP-2 possessed similar pIs to that of WSP-3 and overlapping bands were observed in the gels. These bands segregated independently in F2 and doubled haploid populations, implying two unlinked genes. All three loci were found to be polymorphic: two alleles were detected at the Wsp-2 locus, three at Wsp-3 and two at β-Amy-1. The frequency of alleles at all three loci was found to be different in winter and spring genotypes. Spring genotypes possessed a wider range of phenotypes than winter genotypes. Spring and winter genotypes could be distinguished on the basis of WSP-3 and β- AMY-1 phenotypes. The linkage between Wsp-3 and β-Amy-1 loci and genes controlling spring/winter habit on chromosome 4H is discussed. It is concluded that Wsp-3 and β-Amy-1 can be used as genetic markers for spring/winter habit in barley genetic research and breeding.

J. Watters

Papers

Grain isozyme and ribosomal DNA variability in Hordeum spontaneum populations from Israel.

Water-soluble proteins of mature barley endosperm: genetic control, polymorphism, and linkage with β-amylase and spring/winter habit.