Studies on the induced variability of maize plants following the radiation of the female gametophyte --Romanova, IM, Krivov, NV, Lysikov, VN Radiation mutagenesis one of the promising breeding techniques. Mutations can result from the radiation of maize seed or pollen with different types of radiation. Radiation of female generative structures will make it possible to solve a number of theoretical and practical problems, including the increase of genotypical diversity, the development of the initial genetic stock or donors with improved characteristics. The availability of X-ray units of the Reis type allowed the radiation of plants under field conditions. The power of the exposure dose was 2000 r/min. In our experiments, the radiation was carried out at a distance of the focus objective of 20 mm.

The female gametophyte of maize plants was exposed to the radiation dose ranging between 5 and 70 Gr in 15 treatments. The experimental material produced was soun in the field and the quantitative and qualitative traits of maize plants were studied during the vegetative period in M1. In practical breeding, an appropriate selection of doses, as well as the effect on germinating and producing capacity of plants, are of paramount importance for induced mutagenesis.

Our experiments have shown that the dose curve of the grain content of maize plants exposed to the x-ray radiation of 5-70 Gray at the 3-4 leaf stage has a typically expressed exponential pattern, i.e. the grain content of the maize ear falls with the dose increase by 8-12 times.

The experiments were carried out to analyze the grain content in M2, germinating capacity of the plants in M1.

It has been established that the dose curve of the grain content in M2 changes significantly, acquiring a distinctly expressed peak pattern (Table 1). The one factor dispersion analysis has shown that the grain content per ear in M2 reaches maximum values at the radiation dose of 20 Gray and makes 148.4 ±12.6 and 40 Gray - 135.9 ±10.5 . This increase is statistically significant (P<0.5) and differs from the control values of the grain content making 101.6 ± 9.6. The tendency towards the appearance of peaks on the dose curve is observed in other ranges of x-ray radiation, in particular at the doses of 10 Gray, however, such deviation of the control values is statistically insignificant at the significant level of 95%.

It is noticeable that the dose curve of the M1 germinating capacity is characterised by a trend towards the formation of extrema in the same ranges of the x-ray radiation (Table 1). Thus, one factor dispersion analysis has shown that at the dose of 20 Gray the germinating capacity of plants reaches 62.1 ± 7.3 at 40 Gray it is 47.7 ± 6.4, while in the control it makes 56.9 ± 2.6. However, it should be mentioned that these data at the significant level of 95% differ from the control ones statiscally insignificantly, though such significance at the dose of 20 Gray is already revealed at the significant level of 95%.

The frequency and mutation type arising due to the action of the x-ray radiation on the female gametophyte have been evaluated (Table 2). The highest number of mutations has been found at the radiation doses of 10 Gray (5.7%) and 60 Gray (11.1%), respectively both in the plants and families. At the radiation doses of 20 and 40 Gray, upon which the peaks of germinating capacity in M1 and grain content in M2 are observed, the number of mutations appears to be significantly lower in plants and families and makes 2.9% and 1.7% respectively. The processes of repair are more intensive under these doses.

The experimental data have led us to the conclusion that the exposure of the female gametophyte to the x-ray radiation within the range of 20 - 40 Gray might significantly intensify repair processes in the maize plant resulting in the increase of seed germinating capacity and grain content of ears. The application of target radiation doses might lead to a maximum number of mutations, which is observed at the doses of 10 and 60 Gray, as well as to a desired type of mutation using experimentally established exact doses of x-ray radiation. All these make it possible to significantly reduce the duration needed to obtain desired results, as well as to carry out a target breeding of plants with a maximal possible efficacy.

Table 1. The grain content and germinating capacity after treating female gametophyte with x-ray radiation
 
Treatment Doses (Gr) Grain content per ear Coefficient variation (%) Germinating capacity Coefficient variation (%)
control 101.6 + 9.6 55.6 56.9 + 2.6 14.6
5 97.7 + 11.0 66.7 52.1 + 5.5 41.8
10 129.0+ 8.0 52.7 46.4 + 3.3 34.2
15 84.8 + 9.0 53.1 37.5 + 9.9 95.2
20 148.4 + 12.6 45.0 62.1 + 7.3 43.8
25 131.4 + 12.4 49.1 53.9 + 3.9 36.2
30 115.2 + 8.7 62.9 44.5 + 4.6 51.2
40 135.9 + 10.5 36.3 47.7 + 6.4 42.4
50 105.8 + 12.1 69.8 29.7 + 4.7 73.5
60 99.7 + 11.5 58.9 34.2 + 3.6 43.6
70 80.9 + 10.2 74.7 25.0+ 4.0 69.6

Table 2.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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