In mapping leaf rust resistance genes using Wolfe's multiple marker stocks (Wolfe and Franckowiak, 1991), linkage data among some of the markers were obtained (Table 1). These linkage data were mostly in agreement with the reported linkage relations (Sogaard and Wettstein-Knowles, 1987). The discrepancies found in this study concerned the relations of br1---gs3 and n---lk2 for linkage distance, and e---msg2---v for gene order. The linkage distance is shorter for br1---gs3 and longer for n---lk2 compared with the reported estimates. Also, a more precise placement of the msg5 locus in chromosome 3 is possible based on these data.

The reported gene order among the three gene loci, e, msg2, and v, was e---msg2---v(Hockett and Nilan, 1985; Tsuchiya, 1991). Based on telotrisomic analysis, Tsuchiya (1973) placed the e locus in the short arm and the msg2 in the long arm of chromosome 2. According to this linkage relationship, the phenotypes of E-msg2msg2V- and eeMsg2-vv would be expected in the lowest frequencies of a F₂ population since these phenotypes represent double crossovers. However, the lowest frequencies were Msg2-eeV- and msg2msg2E-vv with frequencies of 4 and 0, respectively, from a population of 687 F₂ plants. The three-point linkage data suggest that the phenotypes of Msg2-eeV- and msg2msg2E-vv should be the phenotypes due to double crossovers, and that the gene order should be msg2-e-v.

References:

Hockett, E.A., and R.A. Nilan. 1985. Genetics. pp. 187-230. In: D.C. Rasmusson, ed., Barley. Madison, USA.

Sogaard, B., and P. von Wettstein-Knowles. 1987. Barley: genes and chromosomes. Carlsberg Res. Commun. 52:123-196.

Tsuchiya, T. 1973. Further information on telotrisomic analysis in barley. BGN 3:75-78.

Tsuchiya, T. 1991. Current linkage maps of barley. BGN 20:92.

Wolfe, R.I., and J.D. Franckowiak. 1991. Multiple dominant and recessive genetic marker stocks in spring barley. BGN 20:117-121.