II. 21. Association of a mildew resistance gene JM1h in Hanna 906 with chromosome 6.
J. Hayashi and H. Heta. Institute for Agricultural and Biological Sciences, Okayama University, Kurashiki (710), Japan.
According to Hiura (1960), Hanna 906 is resistant to race IX, but is susceptible to 10 other races of barley mildew distributed in Japan, and the reactions to these mildew races are controlled by a dominant gene JM1h. In spite of his extensive studies, the location of the gene has not been determined as yet. The present experiment was performed to solve this question by means of trisomic analysis.
Since Tsuchiya's trisomic series, derived from Hordeum spontaneum nigrum, carry a gene JM1sn in common and are resistant to all of the Japanese mildew races, a set of trisomics devoid of the resistant gene JM1sn is needed as the material. Therefore, crosses were made between seven types of Tsuchiya's trisomic plants and a cultivar Shiroto, the latter of which is susceptible to all the mildew races, and from each of the F2 populations of these crosses, a trisomic plant which is susceptible to various mildew races including race IX was selected. Then, these susceptible trisomic plants thus obtained were crossed each with Hanna 906, and the reactions of the F2 seedlings from these crosses to the mildew race IX, innoculated onto them, were examined. Table 1 shows the numbers of the resistant and susceptible plants without classifying them into disomic and trisomic types, because of difficulty of accurate identification of two types at their seedling stage.
As is apparent in this table, in F2 of the cross with Purple trisomic
for chromosome 6 the resistant plants appeared in excess for independent
segregation ratio of 3:1, and the observed counts fitted to a 5:4 ratio
for linkage. On the other hand, independent segregation was confirmed for
other six crosses. This evidence supports the view that the gene JM1h
in
Hanna 906 is located on chromosome 6.
