Chromosome aberrations and the frequency and spectrum of mutations induced by ethylmethane sulphonate in barley and wheat

1. Seeds of diploid and autotetraploid barley and diploid, tetraploid and hexaploid wheat were treated with four different concentrations of ethyl methane sulphonate (EMS). Decreased survival, occurrence of chlorophyll deficient streaks in the leaves and varying degrees of seed sterility were among the prominent changes observed in the M, generation. 2. Mitosis was studied in root-tips fixed 24 hours after treatment from 2x barley and 4x and 6x wheat treated with 400 ppm. of EMS. Chromosome and chromatid breaks and iso-chromosomes occurred in many cells. Interchanges were few. Nearly 15 per cent of the breaks in barley and 50 per cent in 4x and 6x wheat were at the region of the’ primary and secondary constrictions. The high incidence of breaks in EMS treatments at the centric region was also clear from the presence of iso-chromosomes, pseudo-iso-chromosomes and secondary trisomic configurations in the microsporocytes. Disjunctional abnormalities among iso-chromosomes led to the formation of gametes containing deficiencies for whole chromosome arms and consequently to considerable seed sterility. 3. Chlorophyll mutations were abundant in the M2 generation. Viable mutations also occurred at a high frequency in 2x barley but were rare or absent in the wheat species. The relative incidence of different types of chlorophyll mutation varied in EMS and X-ray treatments; also types of chlorophyll mutations never seen in radiation experiments were seen in EMS treated material. 4. It seems possible that the response obtained from EMS treatments may vary from species to species. Polyploids may be less affected than diploids and genes located near the centromere more affected than those farther away. EMS induced mutations may hence provide information on the location of genes within a chromosome. Enhanced variation for quantitative traits may also be generated by EMS through increased recombination in the chromosome segments proximal to the centromere