Relationships between sensitivity of inbred lines to NMU and their mutability

Nine inbreds of maize significantly differing in their physiological response to NMU in M1 were taken for study. Two hundred seeds of each inbred were treated for 24 hours with water solutions of the mutagen at 9 concentrations, over a range from 0.005 mM to 3.2 mM. M3 mutations were selected visually. Mutation frequency was estimated on the basis of the number of M1 selfed plants.

It was found that the inbreds displaying minimum and maximum sensitivity to a depressive action of the mutagen proved more stable against the inbreds of moderate resistance. Curvilinear relationships between unit depression per mM, (DH/Hc)/C, in plant height and mutability (v) was most evident in the variants with optimal frequency of mutation (Fig.).

Similar regularities were shown by E.M. Witkin (1969) in classical experiments with E. coli Strs In our experiment the most sensitive inbreds, Hy2 and Gb834, and the most resistant inbreds, T22 and Gb146, were quite like the supersensitive Uvr+ Rec+ and wild Uvr+ Rec+ strains, and A344 and W23 looked similar to the highly mutable Uvr- Rec+ strain. The similarity in reaction to the mutagen suggests a common universal mechanism of protection and mutability.

Figure.

A. S. Mashnenkov


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