It is well known that the percentage of mutations appearing during maize radiation mutagenesis is comparatively low due to high elimination of seedlings and young plants in the first generation. It is an explanation relating to comparatively high mutation doses--varying within the range of so called crucial i.e. LD50-60 doses.

For increasing maize radiation mutation yields and expansion of their variability spectrum an experiment was carried out for studying the elimination or decreasing of g-ray damaging effects during irradiation of dry maize seeds.

For obtaining the contrasting effect the paternal form of "Début" hybrid bred by S. T. Chalyk and distributed over districts in Moldova was used, which possessed a slightly lower viability as well as higher radiosensivity. For these aims the routinely used (LD50-60) dose of ionizing irradiation was not taken but a slightly higher dose was used instead in the range of 60-70% LD. The maize dry seeds were irradiated by RHM-g-20 installation with 60Co isotope.

For eliminating the 60Co g-ray damaging effect the decision was made to use a number of chemical and physical factors of impact. As the chemical factors 12 substances were utilized: biologically active substances, growth hormones, biostimulators, antioxidants etc. Temperature, U.V. laser hydroelectrolytic products � acidic and basic, i.e. the anodic and cathodic fractions, electromagnetic field of electric current with the industrial frequency and SHF served as factors of physical impact.

Before sowing the maize irradiated seeds were imbibed in solutions of the chemical substances in conventionally used doses and treated with the physical factors also in plant stimulating doses. It is worth noting in addition that LGI-21 U.V. laser on molecular nitrogen was used in the treatment with laser.

The seeds treated in such a way were sown immediately in a field in three-fold replications. In the next field the non-irradiated control was sown as well as the g-irradiated control but with no treatments with chemical or physical factors.

The results of the experiment were determined by counting initial and total appearance of seedlings in all the treatments. Then during the first month of growing plant counting was carried out weekly since it was in this period that the 60Co g-ray negative damaging effect occurred and great elimination of plants weakened by the irradiation happened to take place.

Immediately after seedling appearance it became clear that the real protective effect was shown only by a single chemical substance and two physical factors. But the really highest protection was provided by only one biological stimulator known in our country as "Crossing" ( a patent of the Institute of Plant Physiology AS MR � professor Atimoshae M.V.). The electromagnetic field of electric current with the industrial frequency gave a weaker but still real protection and the effect of SHF was still slightly weaker.

The effect of "Crossing" was remarkable not only due to the fact that the number of seedlings provided by it was 2.5-fold greater, but it caused the least percentage of plants to perish in the first period of their growth. Therefore a 6-fold greater number of plants was maintained in the treatment with "Crossing" than in the irradiated control. It is also of interest to note such a peculiarity: the total number of plants maintained after the "Crossing" treatment was very close to the plant number in the irradiation � free control.

As was mentioned above the effect of the two physical factors electromagnetic field of current with the industrial frequency and SHF were weaker than that of "Crossing" but were still rather significant. Thus the effect of these factors caused a 2-fold greater appearance of early seedlings than in the irradiated control. This difference was slightly less but still significant for the total seedlings.

After elimination of the weakened plants during the first month of their life the electromagnetic field of current with the industrial frequency maintained a 2-fold greater number of plants and the one by SHF was 1.5-fold greater than in the irradiated control.

Though these results are obtained for the first time and demand a thorough verification and a more precise definition, already at present they witness that elimination of the g-ray damaging effect during maize radiation mutagenesis seems to be quite possible.
 

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