1) Agric. Experiment Farm, Hokkaido University, Sappro, 060 Japan
2) Kamikawa Agr. Exp. Station, Nagayama, Hokkaido, 079 (Presently, Hokkaido Green-Bio Institute, Naganuma, 069-13 Japan)
A striped-leaf mutant was found in the M\2\ population of Shimahikari, a Hokkaido rice variety, treated with EMS. This mutant line, called Shimahikari Mu-26, showed fine white stripes in the leaf blades and leaf sheaths throughout the growing period, and also in lemma and palea. When it was crossed with normal strains, the F1 plants were normal and the F2 segregated into 1203 normal and 381 striped (3 crosses pooled), giving a good agreement with the 3:1 ratio. Thus, the striped leaf is controlled by a recessive gene.
Shimahikari Mu-26 was then crossed with linkage testers carrying different leaf-stripe genes, fs-1 (linkage group 6), st-1 (6), st-2 (5), st-4 (4) and st-5 (4). All the F1 plants showed normal chlorophyll development, demonstrating that the mutant gene was not allelic to any of these leaf-stripe genes. When the mutant line was crossed with line No. 283-a carrying the drooping leaf gene (dl) located on linkage group 3, the F2 Showed linkage of the mutant gene for striped leaf with dl. Then, a tester strain MA-89663 having dl and the new leaf-stripe gene was selected from the F2 of Shimahikari Mu-26 X No. 283-a, and was crossed with linkage testers carrying Hg (hairy glume) and bc-1 (brittle culm-1), respectively, in order to determine the location of the new leaf-stripe gene on linkage group 3. The new leaf-stripe gene was linked with dl, Hg and bc-1 with recombination values 14.5, 32.6 and 36.9%, respectively (Table 1). Gene st-3 is known to belong to linkage group 3, but it is closely linked with bc-1 with a recombination value of 1.1% (Iwata et al. 1979). The striped-leaf gene we have found, linked with
Table 1. Linkage relations estimated among st-6(t) and three markers genes in linkage group 3, dl (drooping leaf), Hg (hairy glume) and bc-1 (brittle culm-1)
================================================================ Genes F2 plants with phenotype Recombi- combined Phase of ========================Total nation X2 ========= linkage value (df=3)a A/a B/b AB Ab aB ab (%) ================================================================ st-6 dl Coupling 599 58 65 175 897 14.5+-1.3 1.5 st-6 Hg Coupling 251 45 65 45 406 32.6+-2.9 3.7 st-6 bc-1 Coupling 250 111 111 19 491 36.9+-3.8 1.4 bc-1 dl Repulsion 263 98 104 26b 491 44.4+-3.6 0.6 Hg dl Coupling 270 46 27 63 406 20.2+-2.3 4.9 Hg bc-1 Coupling 232 93 68 34b 427 47.1+-3.5 5.5 ================================================================a-For deviation between observed number and expected number computed from recombination value estimated; all non-significant.
b-The observed numbers did not differ significantly from 9:3:3:1.
Fig. 1. Mapping of linkage group 3 with st-6 and other three genes.
bc-1 with a recombination value of 36.9%, may be considered non-allelic to st-3, but allelism test has not been conducted. It is then symbolized st-6(t). From the result of linkage analysis, the order of the four genes studies is estimated as: bc-1 st-6-dl-Hg as shown in Fig. 1.
References
Iwata, N., H. Satoh and T. Omura, 1979. Linkage studies in rice. New genes belonging to the 11th linkage group. Jpn. J. Breed 29 (Suppl. 2): 182-183. (in Japanese)