In a continuing effort to induce changes in maize, kernels were treated with sodium azide (NaN₃). Maize kernels were pre-soaked in distilled water for 10 hrs. at room temperature. Sodium azide concentrations of 0.001M and 0.01M and a control were used in a phosphate buffer that was adjusted to a pH of 3.0. The treatments were carried out in a hood to vent the fumes. Ninety kernels were treated in 100 ml of the sodium azide solution for 2 hrs. Kernels were then rinsed twice and let stand in distilled water for approximately 1 hr. They were planted in trenches in the field, watered and then covered with moist soil (Briggs, MNL 51:5-6, 1977).

A common measure of effectiveness of a chemical mutagen and apparent genetic effect is to record the amount of physiological damage to the plant. Approximately 30 days after planting the material was rated for plant damage. A rating of 1 indicates no damage, a rating of 9 indicates extreme damage. A. Kleinhofs et al. (Genetic Engineering in Eukaryotes, Plenum, 1983) summarized some of their work on sodium azide in obtaining nitrate reductase mutants in barley. Also see Kleinhofs et al. (Mut. Res. 51:29-35, 1978) for seed treatment procedures and precautions in handling this mutagenic agent. In their paper they used a NaN3 concentration of 10-3M.

Five inbreds were used both in 1984 and 1985 (Table 1); four of these inbreds agree rather well in the plant damage ratings, i.e. within two ratings from year to year. However, there was considerable variability of the mutagen effect from inbred to inbred. In an attempt to explain this variability, the material was classified into germplasm source as Stiff Stalk and Lancaster lines (since all of the lines are proprietary except B73) and also classified by maturity. However, this did not explain the sensitivity of the different lines. Therefore, it appears that there are other factors that determine the sensitivity of each inbred to sodium azide.

If a rating of 6 is considered to show significant damage or effectiveness the 0.01M concentration of NaN3 gave 58% of the inbreds rated 6 or above in 1984 and 60% in 1985. In both years the 0.001M concentration gave 33% of the lines rated 6 or above. Therefore, it is concluded that these doses of NaN3 are in the range of acceptability as based on physiological damage and should be a good starting point for someone wanting to use NaN3 seed treatments.

TABLE 1A. Inbred, dose of NaN3 and Rating for Physiological Damage Associated with the Treatment (1984 Data)

TABLE 1B (1985 Data)

Robert W. Briggs and Andrew R. Bettendorf
 
 

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