Nilan, Kleinhofs, and coworkers (Mut. Res. 17:143, 1973) have demonstrated that azide is an effective mutagen in barley. In maize and other crops, azide treatment of seeds presents several potential advantages over other chemical mutagens. Azide is not classed as a serious mutagen, therefore it is safer than other commonly used chemicals like nitrosoguanidine and ethyl methanesulfonate. Another reported advantage is that seeds have been dried after azide treatment, stored, and planted at a later time without serious physiological damage. This report describes preliminary observations concerning the effectiveness of azide to create mutations in maize.
Inbred A619 seeds were presoaked in aerated water at 28 C in experiment 1 and at 25 C in experiment 2. The duration of the presoak time varied from 4 to 16 hours as shown in the tables. The seed from each presoak time was then treated at the same temperature for 2 hours with 10-3 M sodium azide in 0.1 M phosphate buffer at pH 3.0. Vigorous aeration was maintained during the presoak and treatment periods. Control seed was treated for 2 hours in phosphate buffer without azide. After the treatments were completed the seed was air dried at room temperature and planted within one month.
The M1 plants obtained from treated seed were self pollinated whenever possible and the remainder were crossed to control plants. From each M1 cob, 2 seeds were selected for the M2 generation and were planted in separate plots and reported as replications I and II in the tables. All M2 plants were self pollinated.
Physiological damage observed in M1 plants increased with the length of the presoak time. With 8 hours presoak-azide treatment, the ears on many M1 plants either did not form or ear emergence was delayed. These plants did tassel well. Most 12 and 16 hour presoak-azide treated plants were severely stunted. These plants formed tillers but generally did not form normal ears or tassels.
Kernel mutations were observed in seed from M2 plants including abortive, various defectives, brittle, pale yellow, and viviparous types. A confirmation of the numbers of mutants shown in the tables will be made by demonstrating their heritability in an additional generation. Combined frequencies in experiment I gave kernel mutations of 1% in controls, 6% for 4 hours, and 9% for 8 hours. In experiment II, the frequencies were 3% for controls, 4% for 4 hours, 6% for 8 hours and 15% for 12 hours.
M3 seedling mutations included albino, virescent, yellow, light or yellow green, dwarf, glossy, and photosynthetic types. The frequencies of seedling mutants were 0% for controls, 4% for 4 hours, and 6% for 8 hours in experiment I, and 6% for control, 3% for 4 hours, 8% for eight hours, and 17% for 12 hours in experiment II.
Our preliminary conclusions are that azide treatment of seed does increase the frequency of mutations recovered in maize, but the effectiveness is dependent on the length of the presoak period before azide treatment. Other factors such as the pH of the treatment buffer or the azide concentration may be varied to further improve mutation induction conditions for azide in maize.
Kenneth Hibberd and C. E. Green
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