Effets radiobiologiques de l'irradiation des gametophytes chez l'orge et le ble dur

Spikes of barley and durum wheat were acutely irradiated in the Casaccia field ( 60 Co source) at different developmental stages of their gametophytes. M 1 plants were raised following irradiation of (i) male gametophytes, (ii) female gametophytes and (iii) both male and female gametophytes. The total exposure was 1500 R, 93 R/hr in all cases, while only on both gametophytes for durum wheat, four total exposures were used (750, 1500, 2250 and 3000 R). The radiobiological parameters considered were: M 0 spike fertility, M 1 seed germinability, M 1 seedling and plant abnormality and M 1 spike fertility. The results show that: (1) the female gametophyte is more radioresistant than the male one; (2) the gametophyte radiosensitivity of the two species is very similar; (3) the tetraploidy of the durum wheat allows many altered plants to go through the following generation, moreover these plants show a reduced fertility; in barley, altered genotypes are more precociously eliminated; (4) the developmental stage of the male gametophyte is determinant of the radiosensitivity, even when both gametophytes are irradiated together; (5) the radiosensitivity strongly decreases with progressive gametophyte development; (6) several chromosome aberrations are induced by this type of treatment; those induced during the mononucleate stage very rarely reach the fertilization while those induced during the bi- and trinucleate stages can persist in the successive generation. This is due to the absence of an efficient haplontic selection among the gametes and to the absence of any competition after fertilization, being only one cell: the zygote.