II. 9. Assignment of mutants in Morex to chromosomes.
R.T. Ramage and J.L.A. Eckhoff, U.S.D.A. and Plant Sciences Department, University of Arizona, Tucson, Arizona 85721, U.S.A. "R"
We treated the cultivar Morex, C.I. 15773, with diethyl sulfate and obtained several mutants that promise to be good genetic markers. In an attempt to assign them to chromosomes, we crossed some of them with a tester set of male sterile genes that are closely linked to the centromeres of the 7 chromosomes. The tester set consists of msg10 on chromosome 1, msg2 on 2, msg5 on 3, msg24 on 4, msg1 on 5, msg6 on 6 and msg19 on 7. This tester set has been used to assign genes to chromosomes (Eckhoff and Ramage, 1984a, 1984b). The procedure is to cross a mutant onto each of the 7 male sterile testers, grow the F1's and F2's and classify the F2's for both mutant and male sterility. If a recessive mutant is located close to one of the centromeres, the F2 involving that chromosome should show a deficiency of mutant male sterile plants and the other 6 F2's should show about a 3 male fertile : 1 male sterile ratio in the mutant class.
The F2 classifications involving the critical male sterile genes for 5 mutants that we are assigning to chromosomes are shown in Table 1. For each of the mutants listed in Table 1, the other 6 F2 populations indicated independent inheritance of the mutant and male sterility.
Table 1. Classifications of F2's of crosses of mutants in Morex with male sterile markers.
The short awn mutant that we are assigning to chromosome 1 is a semi-dominant mutant that was described last year (Ramage, 1984). In Table 1, the long awn and medium awn length classes have been combined into one class. The F2 data indicate about 9% recombination between msg10 and the short awn mutant. Tsuchiya (1962) reported a semi-dominant short awn mutant and Tsuchiya and Singh (1972) suggested that it was probably located on either chromosome 1 or 2. We have crossed our mutant with the one reported by Tsuchiya to determine allelism.
We are assigning a light green mutant to chromosome 2. The data in Table 1 does not represent a complete F2. The light green plants were marked with ribbons at flowering and just before harvest a severe wind storm blew off some of the ribbons. We classified the remaining ribboned (light green) plants for male sterility and all male sterile plants for ribbons (light green) and did not find a recombinant plant. A. chlorina mutant, f, and a light green mutant, lg1 have been previously assigned to chromosome 2 (cf. Tsuchiya, 1974, who reported the two mutants to be allelic). We will cross our light green mutant with the chlorina mutant f to determine allelism.
The dwarf mutant that we are assigning to chromosome 2 may be at the same locus as a dwarf gene induced in the cultivar Glacier (Ramage and Ronstadt-Smith, 1983). They reported recombination percentages of 22 between dwarf and row number (Vv), 39 between row number and male sterility (msg2) and 51 between dwarf and male sterility. Corresponding recombination percentages obtained in this study were 16, 13 and 24. Although the recombination percentages are different, the genes are in the same order and relative positions. Ramage and Ronstadt-Smith (1983) stated that large variations in recombination values in this region of chromosome 2 are common and considered the ones that they reported to be overestimations. As all 7 male sterile testers are two-rowed and Morex is six-rowed, we could obtain the percent recombination between row number and plant height in all 7 F2 populations. The recombination percentages in populations involving male steriles on chromosomes 1 to 7 were 14, 16, 10, 19, 19, 15 and 20. The percent recombination between row number and plant height was 17 ± 0.8 for the total (2480 plants) of all 7 F2 populations. We will cross the two dwarf mutants to determine allelism.
The glossy leaf mutant that we are assigning to chromosome 4 has glossy leaf blades and normal leaf sheaths. The data in Table 1 shows a deficiency of male fertile, glossy leaf plants. Glossy leaf plants were marked with ribbons at flowering and just before harvest a severe wind storm blew off some of the ribbons. As a result, some of the glossy leaf plants may have been classified as normals. Four glossy leaf mutants have previously been reported on chromosome 4 (cf. Tsuchiya and Haus, 1973, who reported that g11 and g12 were allelic, as were g13 and g14, and that both loci were on chromosome 4). We will cross our mutant with both g11 and g13 to determine allelism.
The necrotic leaf spot mutant that we are assigning to chromosome 5 may be at the same locus as the necl gene described by Jensen (1971). The data in Table 1 indicate about 10 percent recombination between our mutant and msg1. This is within the range expected between necl and msg1 (Jensen and Jorgensen 1973). We will cross our mutant with necl to determine allelism.
We also crossed a recessive short awn mutant onto the male sterile tester set and classified the F2's. Based on the F2 data, the mutant was not closely linked with any of the 7 male sterile genes, but appeared to be associated with msg24 on chromosome 24. A short awn gene, lk5, has been reported to be on chromosome 4 and several mutants have been reported at that locus (cf. Tsuchiya and Hall, 1978). Also, Eckhoff and Ramage (1984b) have reported a short awn mutant, lk,,f, that may be at the lk5 locus. We will allele test our mutant with both lk5 and lk,,f.
We will grow F3 rows from mutant male fertile F2 plants to confirm linkages. Segregating F3 rows will provide male sterile mutant plants to facilitate allele testing. Also, male sterile mutant plants will be crossed with appropriate genetic markers to obtain multi-point linkage data.
References:
Eckhoff, J.L.A. and R.T. Ramage. 1984a. Use of male sterile mutants linked with centromeres to assign genes to chromosomes. Barley Newsletter 27:41.
Eckhoff, J.L.A, and R.T. Ramage. 1984b. Assignment of a short awn mutant to chromosome 4. BGN 14:20-21.
Jensen, J. 1971. Mapping of 10 mutant genes for necrotic spotting in barley by means of translocations. Barley Genetics II:213-219.
Jensen, J. and J.H. Jorgensen. 1973. Locating some genes on barley chromosome 5. BGN 3:25-27.
Ramage, R.T. 1984. A semi-dominant short awn mutant in Morex. BGN 14:19-20.
Ramage, R.T, and R.S. Ronstadt-Smith. 1983. Location of a light green dwarf mutant on chromosome 2. BGN 13:62-64.
Tsuchiya, T. 1962. Radiation breeding in two-rowed barley. Seiken Ziho 14:21-34.
Tsuchiya, T. 1974. Allelism of f for chlorina and lg for light green (chlorina) in chromosome 2S in barley. BGN 4:79.
Tsuchiya, T. and L.B. Hall. 1978. Telotrisomic analysis of four mutant genes in barley. BGN 8:104-107.
Tsuchiya, T. and T.E. Haus. 1973. Allelism testing in barley. I. Analysis of ten mapped genes. J. Hered. 64:282-284.
Tsuchiya, T. and R.J. Singh. 1972. Trisomic analysis of a short awn
mutant in barley. BGN 2:99.
