GENETIC DIVERSITY OF THE CYTOPLASM IN TRITICUM AND AEGILOPS. III. ON THE ORIGIN OF THE CYTOPLASM OF TWO HEXAPLOID AEGILOPS SPECIES

Genetic characteristics of the cytoplasms in two hexaploid Aegilops species, i.e., Ae. crassa (genome formula DDD2D2McrMcr) and Ae. juvenalis (CuCuDDMjMj), were investigated, by comparing the 18 characters of the normal and cytoplasm substitution lines of two tester cultivars, Chinese Spring and Jones Fife, of commoh wheat (AABBDD). For comparison, the cytoplasms of Ae. squarrosa (DD), Ae. umbellulata (CuCu), Ae. biuncialis (CuCuMbMb) and Ae. ovata (CuCuMoMo) were also studied. The genetic relationships among all these cytoplasms were estimated by two numerico-taxonomical methods. The results indicated that the cytoplasm of hexaploid Ae. crassa is highly similar to that of Ae. squarrosa. The Ae. juvenalis cytoplasm was most closely related to the crassa cytoplasm, and its relation to the squarrosa cytoplasm was not so close. The present results can best be interpreted by assuming that both the Ae. crassa and Ae. juvenalis cytoplasms were derived from Ae. squarrosa. Based on this and other information, evolutionary processes leading to the origin of these two hexaploid species were discussed.