GrainGenes

II.28 Linkage studies in barley.

Ryuhei Takahashi, Jiro Hayashi and Isamu Moriya, The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki 710, Japan.

1. (cer-) gs₈ for a glossy sheath in a cultivar Okaiku 3 (chromosome 2)

Okaiku 3 is characterized by absence of a waxy coating on the upper leaf-sheaths only, differing from the ordinary glossy sheath mutants which lack wax coating on stems and spikes as well as leaf-sheaths. Like other similar mutants this glossy sheath character proved to be controlled by a single recessive gene, named (cer-) gs₈ (previously this was denoted gs₇ in Barley Newsletter 9). A linkage study was made using five crosses made between Okaiku 3 and five genetic marker stocks. The gene gs₈ is regarded to be independent of n and l (chromosome 1), uz, a_n and a_c (3), K and Hs (4), B and trd (5), o (6) and s (7). This suggests that gs₈ might be on chromosome 2. In Table 1 are shown interrelationships between gs₈ and four genes, Pr for colored leaf-tip, v for six-row, e for elongated outer glume and li for ligule-less, all of which are known to be on chromosome 2. The result shows that the gene gs₈ is located very close to e, but far apart from li. In order to determine the distances to gs₈ from v and Pr more accurately, a further test was made with F3 progenies derived from a cross between Okaiku 3 and Nigrinudum. The weighted average values of p among these three genes, estimated from F2 and F3 data, are given in Table 2.

Table 1. Interrelationship between gs₈ for glossy sheath of Okaiku 3 and Pr(Clt) for colored leaf tip, v, e and li in F2 of the crosses with five marker stocks.

Table 2. Weighted average values of p among three genes, gs₈, v and Pr (or Clt) for colored leaf-tip.

Rasmusson and Lambert (1965) have shown that gs₅ is located 2.5 map units from e on chromosome 2. A close proximity of the two loci, gs₅ and gs₈, suggests that these two might be the same one. However, if the glossy sheath character of Jotun (gs₅) is just as is given at the beginning of their paper, namely, waxless on both stems and leaf-sheaths, these two genes may be different. A map of this area of chromosome 2 is shown in Figure 1.

Figure 1. Proposed arrangement of genes on chromosome 2.

References:
Rasmusson, D. C. and Lambert, J. W. 1965. Crop Sci. 5:251-253.
Takahashi, R., Hayashi, J., Moriya, I. and Hirao, Ch. 1966. Barley N. L. (1965) 9:68.
Takahashi, R. and Hayashi, J. 1969. Barley N. L. (1969) 12:59.
 

2. The second gene for six-row - v₂ - on chromosome 7 (KMUT 27)

Dr. Tsuchiya obtained a six-rowed mutant by X-ray irradiation of a two-rowed barley, Svanhals. This appears almost similar to the ordinary six-rowed barley, but the upper- and lowermost two or three lateral spikelets are somewhat underdeveloped in general and often become awn-less and sterile.

The genetic behavior of the mutant six-rowed character was found to be different from that of the ordinary six-rowed character. When the mutant was crossed to a two-rowed form, the resultant F1 plant had two-rowed heads, indicating complete dominance of two-rowed condition. In the F2 generation of such a cross two-rowed and six-rowed plants appeared in a 3:1 ratio (Table 3). On the other hand, a cross with the ordinary six-rowed form gave F1 plants with intermedium heads and in the F2 generation non-six-row and six-row plants appeared in a 9:7 ratio (Table 3). As the result, a gene symbol v₂ was assigned to the new six-rowed mutant gene. This is epistatic to V for 2-row.

Table 3. Segregation of non-six-row and six-row phenotypes in F2 of the crosses of the "six-row" mutant with the ordinary two-row and six-row varieties.

Linkage of v₂ gene was studied using five crosses between the six-rowed mutant and five testers with two-rowed or six-rowed heads. Table 4 shows the relationships between the "six-rowed" head (v₂) and various markers. It is apparent in this table that the "six-row" is inherited independently of n (1), li (2), uz (3), K (4), B and trd (5), and o (6), but is in linkage with s on chromosome 7. In the crosses with 2-rowed forms, excessive numbers of parental character combinations were evident and X²_L's were sufficiently large to conclude the linkage between V₂v₂ and Ss (crosses B and C), although the observed numbers in F2 of the crosses with the ordinary 6-rowed forms (cross E and F) fitted to the calculated numbers on the bases of both independent inheritance and linkage of V₂v₂ with Ss. An F3 progeny test was made further for the cross with Nigrinudum (cross B). Number of F3 families tested were 183 for AB class, 130 for Ab class and 84 for aB class. From the F2 and F3 data, the weighted average values of recombination between v₂ and s were calculated to be 18.98 + 1.457 (%).

Table 4. Interrelationships between non-six-row vs. "six-row" (V₂v₂) and marker character pairs on chromosome 1 - 7 in F2 of the crosses with 6-row mutant.
 

3. Locating of the three mutant genes, gl₃, br₂ and f_k, on chromosome 4.

We have reported in Barley Newsletter Vol. 5 and 11 that three mutant genes, br₂, br₂ and f_k (later amended as f₉ by D. W. Robertson) are all on chromosome 4. The characteristics of the mutants are as follows:

gl₃....a mutant with glossy leaves which occurred spontaneously in a Japanese naked variety of uzu type, called Goseshikoku. The gene was shown to be different from gl and gl₂ by allelic tests.

f₉ (formerly f_k)....an X-ray induced mutant (KMUT 174) found by Tsuchiya is characterized by chlorina leaves from seedling to adult stage throughout, irrespective of whether it is grown under low or high temperature conditions.

br₂....a mutant with short awn, compact head and short culms, which was obtained by X-ray irradiation of a two-rowed variety, Svanhals. This is very similar to the brachytic mutant from "Himalaya" and also uzu type plant, but is distinguished from the latter type by its longer coleoptile without the peculiar projection at its apex.

Interrelationships among these three mutant genes, and K for hooded character and Bl for blue aleurone were studied further by growing F2 and F3 of the following three crosses in all of which a K-gl₃ tester was commonly used as one of the parents.

1. K-gl₃ x Dai-o-byo (blue aleurone)
2. K-gl₃ x Ko A (f9)
3. K-gl₃ x brachytic 2 from Svanhals

Table 5, 6 and 7 show numbers of F2 plants or F3 families of different genotypes used in these three crosses, and the recombination percentages estimated from the data obtained in the respective F2 or F3 tests. A weighted average value of recombination between each character pairs is given in these tables. The results clearly indicate that the five genes, f₉, K, br₂, gl₃ and Bl are arranged on chromosome 4 in this order. A chromosome map is given in Figure 2.

Table 5. Linkage data for f₉ (=f_k), K and gl₃

Table 6. Linkage data for gl₃, Bl and K.

Table 7. Linkage data for br₂, K and gl₃.

Fig. 2. Map of genes on chromosome 4.
 

4. Location of the gene nld for narrow leaved dwarf.

It has already been demonstrated by means of trisomic analysis that a gene for narrow leaved dwarf involved in "Nagaoka Dwarf" mutant is on chromosome 7. The data, together with description of the mutant characteristics, were given in Ber. Ohara Inst. Agric. Biology Vol. 13, pp. 185-198, 1966.

A further study was made thereafter of the interrelationships of the gene nld with several chromosome markers in F2 and F3 of the four crosses with this mutant by means of conventional genetic method. The results shown in Table 8 indicate that nld, s and r are arranged in this order on chromosome 7. It was known also that nld was independent of n (1), v, Pr (2), K, Hs (4) and o (6).

Table 8. Linkage data for nld, r and s on chromosome 7.

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