Effect of Ionizing Radiations and Chemical Mutagens on Chiasma Frequency in Sorghum

抄録

The effect of ionizing radiations (X- and gamma rays) chemical mutagens (EMS, MMS, DES and NEU) and combination treatments on chiasma frequency was studied in the M₁ plants of three varieties (Co 11, Co 12 and Co 18) of Sorghum (2n=20) raised from the treated seeds. All the treatments caused a decrease in chiasma frequency compared to control. There was a marked reduction in the number of bivalents with three chiasmata, while the number of bivalents with one chiasma increased following mutagen treatments. There were differences in the action of different mutagen agents on one hand and a differential response of the varieties on the other. The treatments with chemical mutagens caused a higher reduction in chiasma frequency than radiation treatments. The combination treatments of gamma rays and DES caused a higher reduction, while X-rays+NEU increased the chiasma frequency compared to the single treatments. The factors namely the terminalisation, structural changes, univalent formation and the process leading to chiasma formation are discussed in the light of the present results.