GrainGenes
A Database for Triticeae and Avena
Jensen and Jorgensen, pp. 37-40
II. 18. Location of the yellow rust resistance gene Yr4 on barley chromosome 5.
Jens Jensen and J. Helms Jorgensen, Agricultural Research Department, Research Establishment Riso, DK-4000 Roskilde, Denmark "R"
The short arm of barley chromosome 5 possesses at least six powdery mildew resistance loci and one leaf rust resistance locus. In addition, a yellow rust resistance gene denoted Yr4 (Moseman 1961), or Rps 4d (Johnson and Finch 1976), is reported to be linked to the powdery mildew resistance gene Ml-a with 30 + 3.1 percent recombination (Johnson et al. 1969). The Yr4 gene has also been reported to be linked with gene ms and not linked with genes trd, B and at (Finch and Simpson 1975).
A three-point linkage test was set up by crossing the variety Abed Deba, which has gene Yr4 (Moseman 1971), with a line having genes nec 1a (necrotic leaf spots) and Ml-a, which was selected from the cross 5 x 7 described by Jensen and Jorgensen (1975b). The genotypic F2 segregation was obtained by two progeny tests on F3 seedlings. The material in the first test was inoculated with powdery mlldew culture 59.11 (cf. Jensen and Jorgensen 1975b) and was classified for Ml-a and nec 1a. The segregation for nec 1a was verified in the material in the second test, which was inoculated with a culture of yellow rust, race 23 D (kindly provided by Dr. Eva Fuchs, Braunschweig, FRG) and classified for Yr4.
The segregation and the maximum likelihood linkage estimates are given in Table 1 as the pooled data originating from two F1 plants.
Table 1. Genotypic F2 segregation and linkage estimates from the cross Yr4 x nec 1a Ml-a
The number of F2 plants is not large, and several genotypes are not represented or only represented by one plant. The conditions for calculating a X2 value are thus not fulfilled, which may explain the highly significant X2 values obtained. The recombination percentages show that Yr4 is close to Ml-a, far from nec 1a, and apparently located between Ml-a and nec 1a. On assuming this order of the genes, we estimated the recombination percentages for nec 1a, Yr4 to 47.6 + 3.6 and for Yr4, Ml-a to 6.2 + 1.3; furthermore, we transformed these recombination percentages to map distances in cM (cf. Jensen and Jorgensen 1975a, b). The third distance, nec 1a, Ml-a, is in agreement with that on the current linkage map.
Our data confirm that the Yr4 locus is located on barley chromosome 5, and they suggest that it is between nec 1a and Ml-a, close to Ml-a. This is in agreement with the finding (Finch and Simpson 1975) that Yr4 is linked to the gene ms, which is supposed to be in the centromere region not far from nec 1. The limited number of F2 plant progeny tested, the significant X2-values, and also some heterogeneity between the segregations from the two Fl's used, indicate that our distance estimates may be somewhat biased. However, this possible bias does not explain the discrepancy between our estimate of the distance Yr4, Ml-a of 6.2 percent recombination and that of 30.1 reported by Johnson et al. (1969).
References:
Finch, R. A. and E. Simpson. 1975. In: Annual Report 1974. Plant Breeding Institute Cambridge, p. 136.
Jensen, J. and J. H. Jorgensen. 1975a. The barley chromosome 5 linkage map. I. Literature survey and map estimation procedure. Hereditas 80:5-16.
Jensen, J. and J. H. Jorgensen. 1975b. The barley chromosome 5 linkage map. II Extension of the map with four loci. Ibid. 80:17-26
Johnson, R. and R. A. Finch. 1976. In: Description of Genetic Stocks. Barley Genetics Newsletter 6:130.
Johnson, R., Wolfe, M. S. and P. R. Scott. 1969. In: Annual Report 1968. Plant Breeding Institute Cambridge, p. 122.
Moseman, J. G. 1971. Studies of inheritance of resistance in barley to pathogenic organisms, 1963-1969. Barley Genetics II: 535-541.