Results

1. Radiobiological investigations

The following criteria of the irradiated material and of the X₁-plants were studied :

- the germination of the treated seeds,
- the number and length of culms,
- the number of caryopses per plant,
- the germination of the seeds of the X₁-plants.

Let us first consider the situation within the same level of ploidy. There are great differences in the response of the diploid species T. boeoticum and T. monococcum preferably after having used relatively low dosages. The variety rufinigrum of T. boeoticum turned out to be much more susceptible than T. monococcum var. macedonicum considering seed germination after irradiation. Corresponding observations were also made within the tetraand hexaploid group. T. durum var. valenciae for instance showed a markedly less susceptibility as compared with T. durum var. africanum and T. polonicum var. rubrovesticum. That means, that there are not only differences within the same group but already within the same species. Analogous findings were obtained by MATSUMURA and FUJII (1955) and by MATSUMURA (1956) studying different varieties of the diploid T. monococcum.

According to these findings we cannot expect to obtain a generally valid relation if we consider the response of species or varieties belonging to groups having different chromosome numbers. This can clearly be seen from Figure on the cover. In the left-hand part of this figure, T. boeoticum var. rufinigrum (2n), T. polonicum var. rubrovesticum (4n) and T. aestivum ssp. vulgare var. lutescens (6n) are compared with one another as far as the relations between seed germination and X-ray dosage are concerned. An increasing resistance with increasing degree of ploidy was found. But the opposite situation is illustrated in the right-hand part of the figure. The tetraploid T. durum var. valenciae is more resistant than the hexaploid variety tschermakianum of T. aestivum. Moreover, the variety macedonicum of the diploid T. monococcum does not show the high susceptibility from the diploid material; on the contrary, it is nearly comparable with the hexaploid variety used for this comparison. These findings were confirmed in a second series of investigations.

In general, it can be stated that the varieties valenciae of T. durum (4n) and lutescens of T. aestivum (6n) behaved more resistant to X-rays than all other varieties proved. This regularity became also discernible with regard to the degree of tillering and the culm length in relation to the X-ray dosage. Moreover, the X₁-plants of these two varieties showed a less reduction of their seed production after irradiation than the other ones. Their relatively small susceptibility was also revealed in the low proportion of completely sterile X₁-plants. Finally, the same tendency could be observed with regard to the germination power of the seeds of the X₁-plants.