II.4. A test for allelism of 32 induced six-rowed mutants.
Toshinori Fukuyama, Jiro Hayashi, Isamu Moriya and Ryuhei Takahashi. The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki 710, Japan.
Dr. Tsuchiya obtained two six-rowed mutants, named "Kmut 27 and Kmut 213", from two-rowed cultivars, Svanhals and Hakata 2, respectively by irradiating with X- and gamma ray. They are both somewhat different in their appearance of head from the ordinary six-rowed forms. Kmut 27 is less fertile in the upper and lower lateral spikelets with relatively short awns, and Kmut 213 is characterized by underdeveloped lateral spikelets only in the lower 1/4 of a head, and often by deformed rachilla.
The crosses between these two mutants and a six-rowed cultivar, Natsudaikon Mugi, gave Fl plants with slightly pointed lateral lemmas, while the F1 plants of the crosses with their respective original two-rowed cultivars developed round tipped laterals. Furthermore, the mutual cross between these two mutants resulted in an F1 plant with a two-rowed head, and in the F2, two-rowed and non-two-rowed plants occurred in a 9:7 ratio (Table 1). These facts suggest that the six-rowed characters in these two mutants are controlled by two different recessive genes which are independent of each other. This view may be supported by another fact that the "six-rowed" character of Kmut 213 is independently inherited of the gene s and r on chromosome 7 (Table 2), as Kmut 27 has already been known to involve v2 on chromosome 7 (Takahashi and Hayashi, 1971). A gene symbol v3 is then assigned to the six-rowed character of Kmut 213.
Table 1. Segregation of two-rowed and non-two-rowed plants in F2 of a Kmut 213 X Kmut 27 cross.
Table 2. Interrelationships between "six-rowed" and smooth awn, or short-haired rachilla in F2 of the cross of Kmut 213 with "439", a two-rowed, Syrian local form.
Since a total of 30 other "six-rowed" induced mutants were kindly provided by the courtesy of Dr. A. Möes in Belgium, Dr. E. Pollhamer in Hungary and Dr. F. Scholz in Germany, they were all subjected to the allelic test by crossing with two mutants, Kmut 27 and 213, a six-rowed variety, Natsudaikon Mugi, and their two-rowed parents. Also, a large number of diallelic crosses were made among these new mutants. The shape, size, fertility and awn development of the lateral spikelets of the resultant F1 plants were compared with those of the parental strains or varieties. From the results, at least three types could be classified. The first type, which gave normal six-rowed plants in Fl of the cross with Natsudaikon Mugi, amounted to 23 out of 30 mutants tested. Seven of them, however, had somewhat more elongated pedicels and shorter awn than the other mutants in this group, constituting a subgroup of type 1. Four other mutants behaved almost the same as Kmut 213 and were classified as the second type. The remaining 3 mutants constitute the third group which resemble closely the first group in appearance, though somewhat shorter in lateral awn, but their genetic behavior was different from either of the types 1 or 2: All of them gave F1 plants with intermedium-like heads from the cross of Natsudaikon Mugi, and the crosses with Kmut 27 and Kmut 213 gave F1 with normal two-rowed head. A gene symbol v4 may be given to these new six-rowed mutants. No mutant allelic to v2 in Kmut 27 (class 4) was found among these 30 mutants.
In conclusion, 32 "six-rowed" mutants including Kmut 27 and Kmut 213, were classified into the following four groups and a subgroup.
1. Ordinary six-rowed type controlled by v on chromosome 2, with a subgroup with v'.
2. "Kmut 213" type controlled by v3.
3. The third type controlled by v4.
4. "Kmut 27" type controlled by v2 on chromosome 7.
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