IV.2. Information of linkage and mapping of genes on chromosome 3.

Ryuhei Takahashi. Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Japan

Since the report by Robertson in Barly Genetics II, seven new genes have been shown to be located on chromosome 3.

1. se3 for shrunken endosperm determined by use of several translocations (Jarvi, A. J. and R. F. Eslick, 1971)

2. Est-1 for esterase isozyme activity identified by use of a set of trisomics. (Nielsen, G. and O. Frydenberg, 1971)

3. Sogaard (1971) has reported that three eceriferum mutants are on chromosome 3. Two of them, cer-zn and cer-zd, are on its short arm, and cer-r on its long arm. The relative position of cer-zd, located close to uz, and cer-r proximal to ert-c, in this report is reversed from those shown in the previous report by Fester and Sogaard (1969), probably because the break-point of T3-7 c which was used for tester stock has been moved from the short arm to the long arm.

4. Linkage of bachytic growth in a mutant (B2526) was studied by Holm (1969). It is characterized by a marked reduction in awn and straw lengths, which is conditioned by a recessive gene br_x. Linkages of br_x with the break-points of the four translocations involving segments of chromosome 3 was established. He assumed that the gene might be located distal to x_s, based on the fact that the distance between uz and br_x (42% or independent) was found to be larger than it between uz and x_s, which was suggested by other authors.

5. Takahashi et al. (1966) have indicated that the gene cu2 for curved stems, leaves and awns in a mutant Chôshirô-hen is located on chromosome 3. Interrelationships of cu2 with two genes, als and x_s, which had been known to be located on the distal ends of the short and long arms of chromosome 3, respectively, were studied using crosses of the mutant with two marker stocks, als and Smyrna X_sx_s. The F2 and F3 data below clearly indicate that cu2 is located at the distal end of short arm farther apart than als, but independently inherited of x_s. The suggested arrangement of the four genes are cu2 - als - uz - x_s. An F3 test for the cross between the mutant and als is now in progress.

6. Locations of the gene or genes for resistance to Rhynchosporium secalis (Oudem) Davis and Yd2 for resistance to barley yellow dwar virus disease.

Dyck and Schaller (1961) and Schaller et al. (1964) have determined the locations of Rh3 and Rh4 for scald resistance in relation to x_c for xantha seedling and l_c for dense spike as given in the following map (Fig. 1).

Fig. 1. A map of the genes, Yd2, and Rh3 and Rh4 or Rh. Recombination percentages shown in the lower part of the map are cited from Schaller et al., (1964) and those shown in upper part from Habgood and Heyes (1971).

Recently, Habgood and Hayes (1971) have obtained data as to the genetics and linkage of scald resistance. According to them, there are five alleles at the Rh locus; two are completely dominant (Rhl and Rh2), two incompletely dominant (Rh3 and Rh4) and one recessive (rh5). Moreover, linkage of Rh with uz and st for streak was studied, which gave 12.1-8.3% and 7.7% linkage intensities, respectively. Since the distance of Rh-uz is apparently smaller than the value expected from the data of Schaller et al. (1964), this suggests a possibility that Rh may be located left of a_n.

From the data of Schaller et al., it may be adequate to place Yd2 in the vicinity of uz, although Robertson (1970) placed it between yst2 and l_c. Furthermore, I think l_c must be located between x_c and wst, because Webster (1949) has shown that it is 1.3 unit apart from x_s.

It is regretted that I can find no reliable information reported about the mutant having st and its location. I hope to hear about these, and if possible whether st* and wst are the same gene.

* The gene st was found to be the same as wst (Personal communication from G. W. R. Walker to T. Tsuchiya, February 16, 1972).

7 Are wst and wst3 allelic?**
** See T. Tsuchiya, 1972, BGN 2:103-104

The question was asked me by Tsuchiya. My answer is: We have so far some evidence inconsistent with each other pertaining to this problem, and must await some time until we find a consistent solution of the problem.

Affirmative evidences:
a. Like the Okina-like mutant (wst3), U.S. 163, C.I. 11767 (wst) always segregates about 3% of albino seedlings and pattern of stripes are somewhat different between these two mutants.

b. The mutual cross between these two mutants gives F1 plants with white-striped leaves, almost similar to U.S 163. Similar evidence, though indirect, has been raised by Tsuchiya (personal correspondence).

c. In the F2 population of the same cross are found only striped plants, together with about 11% of albino plants, but no green plants.

Negative evidence:
a. Robertson (1967) has indicated that wst is located between x_c and a_n, 8.8 units apart for a_c. We have found evidence to support the fact that wst is not allelic to wst3 in our preliminary experiment with a U.S. 163 x uz-al cross: several double recessive (recombinant) plants were found among about 600 F2 plants (in repulsion phase).

b. As reported before (Takahashi and Moriya, 1969), wst3 is completely linked with uz; not a single recombinant type plant was found among 1143 F2 plants from two crosses between Okina-like mutant (uz-wst3) and two normal-green varieties (coupling phase). This was confirmed by a further test made using about 4000 F2 plants from these two crosses.

8. A map of the genes on chromosome 3 is given in Fig. 2.

Fig. 2. Map of genes on chromosome 3. The positions in the map of the genes in parenthesis are tentative. The following genes are known to be on this chromosome: ert-c, ert-ii, ari-a, cer-r, cer-zn, cer-zd, se3 and Est-l.

References:

Dyck, P. L. and C. W. Schaller. 1961. Association of two genes for scald resistance with a specific barley chromosome. Can. J. Genet. Cytol. 3:165-169.

Fester, T. and B. Sogaard. 1969 The localization of eceriferum loci in barley. Hereditas 61:327-337.

Habgood, R. M and J. D Hayes. 1971 The inheritance of resistance to Rhynchosporium secalis in barley. Heredity 27:25-37.

Holm, E. 1969. A gene on chromosome 3 in barley leading to brachytic growth. Hereditas 62:419-421.

Jarvi, A. J. and R. F. Eslick. 1971. Linkage studies of shrunken endosperm mutants. Barley Genetics Newsletter 1:22-24.

Nielsen, G. and O. Frydenberg. 1971. Chromosome location of Est-l by analysing F1 trisomic plants BGN 1:35-36

Osler, R. D. Inheritance of rachis length in crosses of accordion rachis. M. Sc. thesis, Colorado A & M. College. Cited from Robertson, D. W. et al 1955 A summary of linkage studies in barley: Supplement II. Agron J 47:418-425.

Robertson, D. W. 1967. Linkage studies of various barley mutants (Hordeum species). Crop Sci. 7:41-42.

Robertson, D. W. 1970. Recent information of linkage and chromosome mapping. Barley Genetics II:220-242.

Schaller, C. W., C. O. Qualset, and J. N. Rutger. 1964 Inheritance and linkage of the Yd2 gene conditioning resistance to the barley yellow dwarf virus disease in barley. Crop Sc. 4:544-548.

Takahashi, R. and Hayashi, J. 1966. Inheritance and linkage studies in barley. II. Ber. Ohara Inst. landw. Biol. 13:185-198.

Takahashi, R. and I. Moriya. 1969. Inheritance and linkage studies in barley. Ber. Ohara Inst. landw. Biol. 15:35-46.

BGN 2 toc
BGN Main Index