Gamma rays emitted by radioactive particles of Co60″, are highly mutagenic. It can not only induce gene mutation but also act as a powerful agent in chromosome and chromatid breakage. A balery plant with 53% pollen and 71% ovule sterility was obtained in the progeny grown from seeds irradiated with 15,000r. Subsequently, this plant produced fewer mature seeds. Meiotic analysis of the microsporocytes collected from this plant showed two isochromosomes, more frequently associated with a ring of four chromosomes than without it. Cytological study of the somatic metaphase, prepared from leaf sheath meristems of the same heterozygous plant revealed a few centromeric breaks adding support to the occurrence of isochromosomes.