| Identification of the genomes involved in reciprocal
translocations in the wild tetraploid wheats Taihachi KAWAHARA and Masatake TANAKA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Mozume, Muko, 617 Japan Several reciprocal translocations of chromosomes have been found among strains of the two wild tetraploid wheats, Tritcum dicoccoides Korn. and T. araraticum Jakubz. (KAWAHARA & TANAKA 1977, 1978, 1981, TANAKA et al. 1979). Of these reciprocal translocation chromosome types, E1 of T. dicoccoides and T1 of T. araraticum were assumed to be the original chromosome structures of the two species, respectively (KAWAHARA & TANAKA 1981). The other types differ from the original ones by one or two translocations. In order to compare the degree of structural differentiation of chromosomes belonging to the different genomes, chromosomes involved in these translocations were identified through crossing experiments with wild diploid wheats, T. boeoticum Boiss. Materials used were nine strains of T. dicoccoides of types E1, E2, E3, E4 and E6, one of T. timopheevi (T1) and nine of T. araticum (T1, T2, T3, T4, T5 and T8). They were crossed by diploid wheats and the chromosome pairings in F1 hybrids were observed. Of nine hybrids of T. dicoccoides with diploid wheats (AAB hybrids), one hybrids involving E6 type formed a quadrivalent per cell. Since no quadrivalent was formed in hybrids of E1 type, this indicates that the translocation between E1 and E6 type are located on two different chromosomes belonging to the A genome. Similarly, identification of genomes involved in other translocations was made by comparing the occurrence of multivalents in PMCs of hybrids with original E1 types with that of hybrids with the other types. Two translocations between E1 and E2 or E3 Were considered to be those between chromosomes of the B genome. The translocation between E1 and E4 possibly involve chromosomes of the A genome and that of the B genome. In hybrids of T. timopheevi or T. araraticum with diploid wheats (AAG hybrids), more multivalents were formed in PMCs than in AAB hybrids. Because chiasma frequencies of AAG hybrids were similar to those of AAB hybrids, this would indicate that the A genome of T. timopheevi and T. araraticum is structurally differentiated from that of diploid wheats. One or two translocations were found between original T1 and the other types. But there was little difference in the occurrence of multivalents between hybrids of T1 type and those of the other types. Probably, these translocations involve no chromosome belonging to the A genome. Based on the present observation and the occurrence of multivalents among translocation types, chromosomes involved in several translocations in T. dicoccoides or T. araraticum were identified. The present results show that the chromosomes of the B or G genomes are more frequently involved in translocations in the tetraploid wheats than those of the A genome. Of five translocations in T. dicoccoides, three were between chromosomes of the B genome, one was between those of the A genome and one was between the A and B genomes. In T. araraticum, all the eight translocations identified were between chromosomes of the G genome. It is concluded that both of the B and G genomes of the tetraploid wheats show higher degree of variability in chromosome structures than that of the A genome. References KAWAHARA, T. & TANAKA, M. 1977. Jpn. J. Genet. 52, 261-267. KAWAHARA, T. & TANAKA, M. 1978. Wheat Inform. Serv. 45-46, 29-31. KAWAHARA, T. & TANAKA, M. 1981. Wheat Inform. Serv. 52, 33. TANAKA, M., KAWAHARA, T. &SANO, J. 1979. Proc. 5th Intern. Wheat Genet. Symp., 73-80. |