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Comparison of radiosensitivities of seven different
genomes of Aegilops, Triticum and Hordeum in terms
of growth inhibition Sadao ICHIKAWA Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Kyoto, Japan Great numbers of radiobiological studies have been carried out in the genus Triticum and some of its relative genera mostly to investigate the relationship between polyploidy and radiosensitivity. However, not many workers have examined the radiosensitivity of each of the various genomes found in these genera. Radiosensitivities of seven different genomes of diploid Aegilops. Triticum and Hordeum species were compared in terms of X-ray-induced growth inhibition. The seven genomes (all n=7) examined were S genome of Aegilops speltoides TAUSCH (KU 2-1), C of Ae. caudata L. (KU 6), Cu of Ae. umbellulata ZHUK. (KU 8-1), M of Ae. comosa SIBTH. et SM. (KU 17-2), D of Ae. squarrosa L. (KU 20-2), A of Triticum monococcum L. (KU 104-2), and the genome of Hordeum distichum L. (cv. Schwanhals). Seeds of these seven species were soaked for 12 hrs. at 20C in dark prior to irradiation, and then exposed to 0.5 and 1 kR of 200 kV X rays at an exposure rate of 95 R/min. For each treatment and for each control 100 seeds were employed. The irradiated and control seeds were sown in wooden flats filled with steamed soil about six hrs. after irradiation (or after about 18-hr. soaking for controls) and placed in a greenhouse. The length of the first leaf was measured 10 and 16 days after irradiation on every seedling emerged. The results obtained are presented in Table 1. At 10 days after irradiation, no very clear differences were found in the responses of the seven species after 0.5 kR treatment. However, obviously different responses to 1 kR of X rays were observed between species. That is, the postirradiation growth of Triticum monococcum was most greatly inhibited while that of Hordeum distichum least affected. Relative growths of five Aegilops species fell between them in the order of Ae. speltoides, Ae. umbellulata, Ae. caudata, Ae. comosa and Ae. squarrosa. More or less recovery of the postirradiation growth is evident for each species from the data taken 16 days after irradiation. Based on these results, it is concluded that the seven genomes have specific radiosensitivities different from each other. The most sensitive genome among them is A, and the sensitivity decreases in the order of S, Cu. C, M, and D, with the Hordeum genome as the least sensitive (most resistant) one. It seems possible to say that the genomes which are believed to be closer to each other cytogenetically than to others show similar sensitivities. An evident correlation is found between the sensitivities of some of these genomes and their interphase chromosome volumes reported earlier (ICHIKAWA and SPARROW 1967, WIS 23/24: 18-20). Namely, the interphase chromosome volumes measured for Triticum monococcum (A), Aegilops speltoides (S), Ae. squarrosa (D) and Hordeum vulgare (having the same genome with H. distichum) were 17.9, 16.7, 15.8 and 13.4 micro3, respectively. These values are obviously correlated with the order of sensitivity determined in the present study, supporting our earlier demonstration that the plants with larger interphase chromosome volumes are more radiosensitive (SPARROW et al. 1965, Radiation Botany 5, Suppl.: 101- 132; ICHIKAWA and SPARROW 1967, Radiation Botany 7: 429-441). (Received November 28, 1968) |