II. 22. Trisomic analysis of a fragile stem mutant found in Kobinkatagi 4.
J. Hayashi and I. Moriya. Institute for Agricultural and Biological Sciences, Okayama University, Kurashiki (710), Japan.
A spontaneous mutant characterized by fragile stems and leaves was found in a Japanese naked barley, Kobinkatagi 4. Another feature of this mutant is its dwarf growth: it is only about 70% in height of the original variety at all stages from seedling to adult. Since the mutant character was found to be controlled by a single recessive gene, the linkage of the gene was studied by means of trisomic analysis. In F2 of the crosses between the mutant and Tsuchiya's seven types of trisomics derived from H. spontaneum nigrum, the segregation of the normal and fragile stem characters was examined. The results are shown in Table 1.
It is apparent in this table that the gene for fragile stem is not located
in any of the chromosomes 2 to 7: segregation of the normal vs. fragile
stem character in both the disomic and trisomic classes in F2 of these
six crosses occurred in a 3:1 ratio. On the other hand, in F2 of the cross
with Bush having chromosome 1 in excess, the mutant type plants were found
far less from the expected number for independent segregation, and the
observed counts in the disomic class fitted well to the expected number
for trisomic segregation ratio of 8:1. Therefore, it is doubtless that
the gene for fragile stem mutant occurring in Kobinkatagi 4 is located
on chromosome 1. Since two other known genes for the similar fragile stem
a character, fs in Kamairazu and fs-2 in Oshiehi-hen, are
known to be on chromosomes 7 and 5, respectively, the new gene in this
mutant can be designated as fs-3.
