IV. 6. Coordinator's Report: Chromosome 5.
Jens Jensen, Agricultural Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark.
A gene designated Mdh-Hl coding for malate dehydrogenase was associated with the long arm of crhomosome 5 and another gene designated Pgi H1 (probably a misprint of Pgi-Hl), coding for phosphoglucose isomerase was associated with the short arm of chromosome 5 (Powling et al. 1981). Both associations were done by means of electrophoresis on wheat-barley addition lines, where chromosomes of barley were added to the wheat genomes, and of a wheat line, in which the short arm of barley chromosome 5 was translocated to wheat chromosome 2A. Powling et al. (1981) also used this method to associate genes that were coding for two proteins, separated by electrophoresis and thought to be prolamins, with the short arm of chromosome 5 (they are probably loci Horl and Hor2). One more band occurring in the electrophoresis and thought by them to be glutelin was genetically controlled by the long arm of chromosome 5. This controlling factor may be the same as that referred to by Miflin and Shewry (1981) as locus Hor3.
Previously described alleles as well as several additional alleles in the Horl and Hor2 loci were associated with 60 varieties (Linde-Laursen and Doll 1981).
The data used for testing recombination between alleles in the Ml-a powdery mildew resistance locus (or region of genes) (Giese et al. 1980) referred to in last year's coordinator's report were further verified (Giese et al. 1981). Of the four previously reported recombinants in the Ml-a locus, three were ruled out and the one remaining was questioned. It was indicated (Giese et al. 1981) that the Ml-a4 gene is identical with Ml-k, and it was proposed that only the Ml-k symbol should be used in the future. Furthermore, Giese et al. (1981) reports a number of recombination percentages between the Ml-k and the Ml-a loci (see below).
In a review (Giese 1981), the occurrence of and recombination between powdery mildew resistance genes at loci Ml-k and Ml-a were collected.
A map of chromosome 5 identical with the one prepared for the last coordinator's report was presented at the Barley Genetics Symposium at Edinburgh by the coordinator; in addition, standard deviations regarding all possible distances on the map were given in a table.
A linkage map (Figure 1) is estimated as usual by the map estimation procedure previously described. All the data used to estimate the map in last year's report were utilized. In addition, the following recombination percentages between loci Ml-k and Ml-a reported by Giese et al. (1981) were utilized: 5.40 + 1.16, 5.52 + 1.16, 7.51 + 1.21, 8.82 + 1.06, and 8.94 + 1.18, whereas that of 9.98 + 1.36 did not fit the map and was omitted. The data providing the recombination percentage of 11.69 + 1.29 have been considered previously and were not considered anew.
As gene Ml-a4 is now considered to be gene Ml-k (Giese et al. 1981) and based on conclusions attained by Giese (1981) the following recombination percentages in older literature can now be considered as recombination percentages between Ml-k and Ml-a. Of those the following fitted into the map and were thus utilized in the map estimate: 6.0 + 2.6, 6.2 + 1.3, 6.4 + 1.5, 6.5 + 1.6, 6.8 + 1.6, 7.6 + 1.1, 8.1 + 1.4, 9.1 + 3.4, and 16.7 + 6.9 (Wiberg 1974). The following recombination percentages between Ml-k and Ml-a did not fit into the map and were not utilized in the map estimate: 1.3 + 0.8, 4.2 + 0.9, 14.8 + 2.2, 15.2 + 3.4 (Wiberg 1974), and 4.87 + 1.00 (Jørgensen and Moseman 1971). Furthermore, Wiberg (1974) reports four crosses with expected 15:1 segregation between Ml-at and M1-(1063) which is now considered as Ml-k. Linkage was reported in one of the crosses. A combined estimate of the recombination percentages from the four crosses of 44.7 + 2.7 calculated by the coordinator did not fit into the map and was therefore not utilized in the map estimate.
The estimated map is drawn in Figure 1. The inclusion of the above-mentioned data in the map estimate introduces only small changes; its main contribution is to improve the estimate of the distance between Ml-k and Ml-a, which is now 7.43 + 0.29 cM. More than half of the information regarding this distance comes from recombination percentages considered for the first time this year, but even before these data were included this distance was the one determined most precisely on the map. The distances from Ml-k and Ml-a to the five loci that control hordein are also well determined, whereas this group of seven loci is not too well positioned in relation to the loci that control morphological characters in lower positions on the map. The other loci that control disease resistance reactions on the short arm of chromosome 5 are those having the poorest localization of the mapped loci.
References:
Giese, H. 1981. Powdery mildew resistance genes in the Ml-a and Ml-k regions on barley chromosome 5. Hereditas 95:51-62.
Giese, H., H. P. Jensen, and J. H. Jørgensen. 1980. Allelism of genes in the Ml-a locus. BGN 10:22-24.
Giese, H., J. H. Jørgensen, H. P. Jensen, and J. Jensen. 1981. Linkage relationships of ten powdery mildew resistance genes on barley chromosome 5. Hereditas 95:43:50.
Jørgensen, J. H. and J. G. Moseman. 1971. Two new genes at the Ml-a locus in barley for resistance to Erysiphe graminis f. sp. hordei. Z. Pflanzenzuchtg. 66:67-75.
Linde-Laursen, I. and H. Doll. 1981. Alleles present in loci Horl and Hor2 in a pedigree of European barley. BGN 11:43-45.
Miflin, B. J. and P. R. Shewry. 1981. The genes for the storage proteins of barley. Abstr. XIII Int. Bot. Congress, Australia, 1981.
Powling, A., A.K.M.R. Islam, and K. W. Shepherd. 1981. Isozymes in wheat-barley hybrid derivative lines. Biochem. Genet. 19:237-254.
Wiberg, A. 1974. Genetical studies of spontaneous sources of resistance to powdery mildew in barley. Hereditas 77:89-148.
