II.13 Reverse mutation at the ligule-less locus (li) of barley.
Takeo Konishi. The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Japan.
A ligule-less mutant is serviceable as a favorable material for reverse mutation study with the following three merits: (1) a qualitative change which is easily and clearly identifiable at the early seedling stage, (2) a large number of individuals can be treated for a higher plant, and (3) a viable change which can be further pursued as to its genetic behavior.
The mutagen-treated M1 individuals and their original ligule-less strains were grown in the isolated field, and before anthesis, each of four spikes per plant were bagged for preventing outcross. Thirty seedlings per M1 spike progeny were examined for appearance of a reverse mutant in M2. The mutation frequency was represented by the proportion of reverse mutants to total seedlings observed.
1) Spontaneous reversion frequencs in six ligule-less strains.
A test of allelism indicated that the ligule-less genes in the six strains hitherto preserved in our institute are at the same li locus on chromosome 2. Nevertheless, two strains, OUM 1 and Chikurin li, differed markedly in spontaneous revertibility from the other four strains in which no mutant was observed (Table 1). It is noteworthy that such high frequencies of the reversion in these two strains have never been observed in any other cases of barley.
Table 1. Spontaneous reversion frequency in six ligule-less strains.
2) Mutagenic effects of gamma-rays and EMS treatments on reversion in OUM 1.
Dry seeds of revertible OUM 1 were divided into two parts and treated each by three doses of gamma-rays and EMS, respectively, and mutagenic effects of the two agents on reversion were compared in M2 seedlings.
According to Table 2, both treatments seem to be effective of increasing the reversion frequency to an extent, though the increment from the control was not statistically significant. It is pointed out in the result that EMS-treatment gave more than one revertant per M1 spike progeny, simply called here "multiple" event, occurring 6 times. However, in the gamma-rays treated plots, and the control as well, no multiple, but only a "single", event was found.
A progeny test revealed that some of the mutants, derived from multiple events, bred true to the normal (reverted) type, while all others, including revertants from single events, were heterozygous for the mutant gene, segregating the normal and ligule-less types in a ratio of 3 : 1.
As shown in Table 3, segregation of normal and ligule-less types in the hybrids of two revertants with OUM 1 and its original variety, Akashinriki, indicated that the reversion was controlled by a single dominant mutant gene at the same li locus.
The tentative conclusions from these results are: (1) there exist iso-alleles in the ligule-less mutants, (2) treatments with mutagens, especially with EMS, promote the reversion from the ligule-less mutation, (3) the reversion is due to a single dominant mutation at the li locus and (4) whenever a mutation occurred, the revertant can be easily detected, even if it is heterozygous for the gene.
