GrainGenes

II.21. Realization of mutations in M2-families due to diplont and haplont selection.

M. R. Kozachenko. Ukrainian Institute of Plant Industry, Plant Breeding and Genetics, Kharkov, U.S.S.R.

The investigations of mutation variability in the progeny of each M1-plant grown from spring barley seeds treated with chemical supermutagens and gamma-rays have shown that, as a rule, one of all M2-families (M1-ear progenies) was mutant. More than one mutant M2-family in the progeny of the same M1-plant has been observed only rarely. A single mutant family usually possesses only one mutation. Several types of mutations have been observed with some M2-families (2-3 pigmentary ones; 2-3 mutation groups; pigmentary, open-flowering sterile, morphophysiological ones).

It has been found during these investigations that all plants (with no exceptions) in one of M2-families in the progeny of some M1-plants had mutation phenotypically of the same type (pigmentary, open-flowering sterile). It should be noted here that dominant mutations have not been observed in any M1-plant, and thus all mutations under study were recessive ones.

Some cases have been observed when all M2-families (the progeny of the same M1-plant) had the same mutation (pigmentary, open-flowering sterile or morphological one). Some authors tend to explain the latter phenomenon by crossing-over effects.

However, all the above mentioned phenomena seem to be attributed to mutations of one or more factors and phenotypical realization of mutations in the process of development of mutant variation and also in the process of haplont & diplont selections during M1- and M2-plant development and reproduction. Really those changes in M2 may be found, which arose in the apical point of embryos in treated air-dried seeds. When separate tissues giving rise to reproductive organs of individual spikelets of M1-plants arose from mutant cells, then each stem and inflorescence on it may be heterogeneous (chimaerous) by this mutation. Therefore, with no further diplont or haplont selection, a certain number of seeds homozygous for the mutation will be formed in the inflorescence (1:3 ratio, theoretically), and the mutant variation may be observed in all M2-families (the progeny of the same M1-plant). In the cases of one or several embryonic stalks being chimaerous by mutation, mutants may be found in one or several M2-families, respectively. Moreover, when different mutant cells have arisen, the progeny of the same M1-plant may involve different mutant families; and with several mutating factors in one cell, several mutations in the same M2-family may arise. When the haplont selection or homozygotization by mutation happens in all spikelets on one of M1-plant stalks, then all kernels formed in these spikelets and, therefore, all plants of M2-family will have the mutation of the same type.

The determination of mutation frequencies in M2 should be performed with the view of such a realization of mutations in the process of M1-plant development. In this case the most objective method of estimation of realized mutability seems to be counting the number of all M2-mutations cases per 100 progenies of M1-plants.

References:

Kozachenko, M. R. and V. T. Manzyuk. 1972. Mutation variability in barley as depending on chemical supermutagens, their concentrations, cultivar genotypes and realization of mutation in M1- and M2-plant ontogenesis. In: "Nauchnye trudy kharkovskogo otdeleniya VOGIS im. N.I. Vavilova. Kharkov, U.S.S.R. (In press).

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