X-ray Induced Chromosomal Aberrations in <i>Hordeum</i>

Abstract

X-ray treatment was applied to dormant seeds of Hordeum spontaneum C. Koch var. transcaspicum Vav. by Matsuda's Type KXC-17 apparatus at 180kVp, 3mA, no filter. The dose was about 13, 500r units. Seventy eight plants in X2 generation which were raised from semi-fertile (fertility less than 50%) X1 plants were cytologically investigated. The results are summarized as follows:1. Chromosome interchanges were observed in 13 plants from 9 head progenies. One ring of eight, 2 ring of four, and one ring of four were observed in 1, 2, and 9 diploid plants, respectively (Tab. 1).2. One of two trisomic plants showed the chromosome associations of 1V+5II and 1III+6II at diakinesis and MI, indicating the tertiary nature of the trisomics (Tab. 2).3. Nucleolus-chromosome relationships were determined in all plants with reciprocal translocations (Tab. 2). The ring of eight (Figs. 4a, b), one of the two rings of four in one of the 2 (4)+(4)-plants and the ring of four in 4 (4)-plants (Figs. 1, 2) were attached to the nucleolus, which showed that a member of the interchange was the nucleolus chromosome (chromosome 6 or g-chromosome).4. In one plant a complete failure of pairing was observed, almost all of the chromosomes being univalents at diakinesis and MI. The meiotic process was very irregular followed by complete sterility on both female and male sides.5. The results of Burnham and Hagberg (1956) indicating that the breakage frequency of a certain chromosome varies according to the variety are confirmed.6. The occurrence of trisomic plants in the progeny of interchange heterozygotes is mentioned.