GENETIC DIVERSITY OF THE CYTOPLASM IN TRITICUM AND AEGILOPS

V. CLASSIFICATION OF 23 CYTOPLASMS INTO EIGHT PLASMA TYPES

Abstract

We are attempting to produce nucleus-cytoplasm hybrids in all possible combinations between the nuclei of twelve strains of common wheat covering the wide range of its genetic variation, and the cytoplasms of 22 species of Triticum and Aegilops (including one synthetic amphiploid) representing almost all basic genome types known in the two genera. Though their production is still far from completion, comparative studies of the hybrids under development indicated that great genetic diversity of the cytoplasm exists among the species of the two genera, and their cytoplasms can be classified into several major plasma types. The results of the studies were reported here. First, brief description was given to individual cytoplasms as to their genetic effects on the character expression of common wheats. Second, genetic similarities between the cytoplasms were evaluated in two ways, (1) from their effects on 15 characters of CS and (2) from their effects on the self ed seed fertility of twelve common wheats; both evaluations were made in the form of genetic distance, based on which the cytoplasms were clustered. From these results, the following eight major plasma types were distinguished: (1) A type-the cytoplasm of T. boeoticum (haploid genome constitution A), causing growth depression, severe winter killing, variegation in winter and severe male sterility, (2) C type-the cytoplasm of Ae. caudata (C) causing pistillody, male sterility and haploid formation, (3) C^u type-the cytoplasms of Ae. umbellulata (C^u), Ae. triuncialis (CC^u), Ae. biuncialis (C^uM^b), Ae. columnaris (C^uM^c) and Ae. triaristata (C^uM^tM^t2), causing growth depression, variegation in winter, male sterility and haploid formation, (4) D type-the cytoplasms of Ae. squarrosa (D), Ae. cylindrica (CD), Ae. juvenalis (C^uDM^j), Ae. crassa (DD²M^cr), and Ae. vavilovii (DM^crS^p), causing no remarkable effects, (5) G type-the cytoplasms of T. dicoccoides var. nudiglumis (AG) and T. timopheevi (AG) causing anther malformation and male sterility, (6) M type-the cytoplasm of Ae. ovata (C^uM^o) causing extreme delay of heading and male sterility, (7) S type-the cytoplasms of Ae. speltoides (S), Ae. kotschyi (C^uS^v), Ae. variabilis (C^uS^v), T. dicoccoides var. spontaneo-nigrum (AB), T. dicoccum (AB), and common wheat (ABD) with no remarkable effects, and (8) S¹ type-the cytoplasm of Ae. sharonensis (S¹) causing growth depression and male sterility. Five additional cytoplasms studied by previous workers were also classified according to these types. From the genetic similarities observed, descents of the cytoplasms in polyploid species were clarified, , tracing their origin back to one of their parental species.