| Development of reciprocal translocation homokaryotypic
lines by X-rays irradiation of polyhaploid in wide cross hybrid N. Nakata, Y. Yasumuro and M. Sasaki Faculty of Agriculture, Tottori University, Tottori 680, Japan X-rays irradiation is well known to be useful in inducing chromosomal translocation. In wheat breeding Sears (1956) and Knott (1968) used X-rays irradiation to translocate alien genes into wheat chromosomes. However in the case of X-rays irradiation of disomic plant the induced translocations are mostly heterozygous. Therefore a translocation homozygote must be selected from the selfed progeny of a heterokaryotype. We propose the following procedures using polyhaploids for the development of reciprocal translocation homozygotes; (1) irradiating polyhaploid materiai seeds or calli with X-rays to induce translocations, (2) treating the irradiated polyhaploid materials with colchicine solution to obtain fertile plants. As a result, any chromosomal changes induced in the polyhaploid cells should be present in a state of homokaryotype due to chromosome doubling. As an example, the scheme of the development of reciprocal translocation homozygotes from wheat x rye polyhaploids is shown in Fig. 1. An experiment was made on wheat-rye polyhaploid hybrids. The polyhaploid seeds between the common wheat variety Chinese Spring and inbred rye lines were irradiated with X-rays (15-40 kR) and then the plants from the irradiated seeds were treated with 0.05% colchicine solution at the 2-3 tiller stage in order to recover seed fertility. In the progenies (X2C2) of the fertile plants obtained chromosomal structural changes were cytologically identified by the modified method of acetocarmine-Giemsa staining (Nakata et al 1977) where the Wright solution was used instead of the Giemsa solution. As the result, 44 translocated chromosomes were identified in 19 out of 65 X2C2 lines examined and were present as homokaryotype. 77.3% (34 chromosomes of 17 pairs) of 44 translocated chromosomes were the products of reciprocal translocations. Most of translocations were noncentric translocations, that is, most of translocated positions were located on interstitial regions of chromosome arms. 10 out of 17 pairs of reciprocal translocations occurred between chromosomes of rye and of wheat. However only two pairs (5B-5R and 6B-6R) were between homoeologous chromosomes. The result indicates that in the procedures using polyhaploid the reciprocal translocations occur independently from homoeologous group, and translocated chromosomes become homozygous in the fertile progeny obtained. If in remote crossing a hybrid is scarcely obtained, reciprocal translocations can be induced in the calli initiated from particular organs (young spike segments, embryo and so on) of the polyhaploid hybrids. In our Laboratory the polyhaploid calli between three Aegilops species and rye were irradiated with X-rays of 625, 1250, 2500 and 5000 R. These calli were induced from young spikes of the respective hybrid. X-rays of 5000R inhibited the growth and regeneration of calli. However X-rays of other doses did not noticeably affect the growth and regeneration of the calli and induced chromosomal structural changes in the callus cells. And, a plant was obtained having reciplocal translocation between chromosomes of Ae. umbellulata and rye among regenerated plants from the irradiated calli. Thus the procedures that combine polyhaploid as material, X-rays irradiation for induction of translocation and colchicine treatment for chromosome doubling are useful in developing a reciprocal translocation homozygote in wide cross hybrid. Reference Knott, DR (1968) Translocations involving Triticum chromosomes and Agropyron chromosomes carrying rust resistance. Can J Genet Cytol 10: 695-696 Nakata N, Yasumuro Y and Sasaki M (1977) An acetocarmine-Giemsa staining of rye chromosomes. Jpn J Genet 52: 315-318 Sears ER (1956) The transfer of leaf-rust resistance from Aegilops umbellulata to wheat. in "Genetics in Plant Breeding", Brookhaven Symp Biol 2: 1-22 |