For phosphogluconate dehydrogenase isozyme of barley, the Pgdl and Pgd2 loci are detected. At the Pgd2 locus, two alleles are designated as Ps allele for 'Pallas' and Tn for 'Tern' (Nielsen and Johansen, 1986), and the locus is located in the long arm of chromosome 5 (Jensen, 1990). Meanwhile, at the Pgdl locus, Brown et al. (1978) found genetic variation in natural populations of wild barley (Hordeum spontaneum), but Kahler et al. (1980) and Nielsen and Johansen (1986) could not find any allelic variation in cultivated barley. Recently, Konishi and Yoshimi (1993) found a few barley accessions to carry a new variant allele which is named as Tj allele from Thomje 1, while the other or normal one is designated as Ak allele from 'Akashinriki' of a Japanese cultivar. Among more than 3,000 accessions of cultivated and wild barleys examined, only three accessions of cultivated barley were detected to possess the Tj allele. They were, Thomje 1 and Tomlung collected from Central and Eastern Nepal, respectively, and K 12 sent from India.
From the result that the Pgdl locus was found to be located on chromosome 1 using wheatbarley addition lines (Shepherd and Islam, 1987), K 12 carrying the Tj allelewas crossed with three linkage testers, OUL 135 (gl5, br, n, and 1), OUL 126 (f5), and OUL 003 (fc), respectively. Segregation for the marker genes was investigated in their F2 populations. The results are shown in Table 1. The Pgdl locus is independent of two markers, n (naked caryopsis) and 1 (dense spike), in the long arm of the chromosome 1, while the Pgdl locus is linked with the following markers in the short arm of the chromosome: gl5 (glossy seedling), br (brachytic plant), f5 (chlorina seedling-5) and fc (chlorina seedling of Colsess V). From the recombination values shown in Table 1, the f1ve loci are arranged in the order of gl5-br-fc-Pgdl-f5 (see editor's note) from the proximal to the terminal of the short arm of chromosome 1, as illustrated in Fig. 1.
References:
Brown, A. H. D., E. Nevo, D. Zohary, and O. Dagon. 1978. Genetic variation in natural populations of wild barley (Hordeum spontaneum). Genetica 49:97-108.
Jensen, J. 1990. Coordinator's report: Chromosome 5. BGN 20:78-80.
Kahler, A. L., S. Heath-Pagliuso, and R. W. Allard. 1981. Genetics of isozyme variants in barley. II. 6-phosphogluconate dehydrogenase, glutamate oxalate transaminase, and acid phosphatase. Crop Sci. 21:536-540.
Konishi, T., and R. Yoshimi. 1993. Geographical distribution of isozyme alleles for phosphogluconate dehydrogenase in barley. Genome 36:512-516.
Nielsen, G., and H. B. Johansen. 1986. Proposal for the identification of barley varieties based on the genotypes for 2 hordein and 39 isoenzyme loci of 47 reference varieties. Euphytica 35:717-728.
Shepherd, K. W., and A. K. M. R. Islam. 1987. Cytogenetic manipulation of barley chromosomes in a wheat background. Barley Genetics V:375-387.
Wettstein-Knowles, P. von. 1992. Cloned and mapped genes: Current status. pp. 73-98. In P. R. Shewry (ed.), Barley: Genetics, Biochemistry, Molecular Biology and Biotechnology. Alden Press, Oxford.
Editor's note - The f5 loci may be located between gl5 and br because the suggested arrangement would place f5 beyond the telomere in the molecular map for chromosome 1S.