Effect of x-ray irradiation on maize inbred line B73 tissue cultures and regenerated plants

In order to enhance variation induced by the tissue culture process and to obtain agronomically desirable mutants, friable embryogenic tissue cultures of maize (Zea mays L.) inbred line B73 were x-ray irradiated with 11 doses [0-8.4 kilorads (kR)]. Reductions in callus growth rate and embryogenic callus formation occurred with increasing x-ray doses 20 d and 3 months after irradiation. Callus irradiated with 0.8 kR showed a significant increase in growth rate and a 20% increase in embryogenic callus 9 months after irradiation. A total of 230 R0 plants were regenerated for evaluation. Pollen fertility and seed set of R0 plants decreased with increasing x-ray dosage. Days to anthesis and plant height of R0 plants varied among x-ray treatments but were generally reduced with higher dosages. The number of chromosomal aberrations increased with x-ray dosage. The R1 seeds taken from R0 plants were also grown and tested for mutant segregation. Plants regenerated from irradiated calli had a two- to 10-fold increase in mutations over plants regenerated from unirradiated control callus. Germination frequency of seeds from R0 plants decreased with increasing x-ray dosage. Although chlorophyll mutants were most frequently observed, a number of vigorous plants with earlier anthesis date were also recovered