| I. Research Notes Cytoplasmic relationship between Triticum boeoticum and T. urartu H.S. DHALIWAL Department of Plant sciences, University ot California Riverside, CA 92502, U.S.A. The nucleus of one species can be substituted into the cytoplasm of another related species by repeated backcrossing. Information on male fertility/sterility interactions from such nuclear substitution lines has been used to establish cytoplasmic relationships among various Triticum and Aegilops species (MAAN and LUCKEN 1970, 1971 and SUEMOTO 1973). The cytoplasmic relationship between the diploid wheats T. boeoticum and T.urartu, based upon nucleo-cytoplasmic interaction, has not been reported thus far. In spite of the fact that T. urartu is reproductively isolated from T. boeoticum throughout the range of their sympatric distribution in Transcaucasia, Turkey, Iran. Iraq and Lebanon ; it was not previovsly considered a distinct species but a different form of T. boeoticum. Recently,T. urartu; has also been considered as the B genome donor to the tetraploid wheats (JOHNSON 1975, DHALIWAL and JOHNSON 1976). This paper reports a study of the cytoplasmic relationship between T. boeoticum (2587) and T. urartu (1545) following development of nuclear substitution lines. To substitute the T. urartu genome into T. boeoticum cytoplasm, T. boeoticum was used as the female parent and T. urartu as the pollen parent. The boeoticum x urartu F1 hybrid was completely male sterile. The sterile F1 hybrid was used as the seed parent and backcrossed with its parental urartu line. The first backcross progeny (BC1F1) segregated for sterility with plants ranging from completely sterile to a few partially fertile. The completely sterile BC1F1 plants were backcrossed with T. urartu. The BC5F1 plants resembled T. urartu on several morphological characters e.g. glabrous leaves, glabrous leaf sheath, glabrous glumes, presence of a third awn in the spikelet, short and divergent awns, and dense spike indicating that the T. urartu genome was almost completely reconstituted in the boeoticum cytoplasm. Theoretically 98.43% of the urartu genome should have been substituted after five backcrosses. Three plants obtained in the BC5F1 were morphologically uniform and were completely male sterile in spite of normal meiosis with seven bivalents at metaphase I. Anthers were irregularly developed and never protrude from the florets. The plants were, however, female fertile as partial seed set was obtained on backcrossing with either T. urartu or T. boeoticum. The complete male sterility of plants produced by substituting the T. urartu genome into T. boeoticum cytoplasm suggested that the two speceies have different cytoplasms. Male sterility of the urartu genome in boeoticum cytoplasm may be due to the failure of boeoticum cytoplasm to translate or to activate a fraction of the urartu genome responsible for male gametophyte development as effectively as that of the urartu cytoplasm. These results are consistent with the observed difference in behaviour of reciprocal crosses involving T. boeoticum and T. urartu JONSON and DHALIWAL, in press. When T. boeoticum is used as the female parent and to urartu as the pollen parent, the F1 hybrid seeds are extremely reduced in size but are viable whereas in the reciprocal cross, the F1 seeds are of normal length but are shrivelled and non-viable. Frequently such differential phenotypic effects in reciprocal crosses of related species are attributed to differences in their cytoplasms. A few plants of the hybrid involving T. urartu (1545) as the female parent and T. boeoticum (1195) as the male parent were obtained by embryo culture. The sterile urartu x boeoticum hybrid is being backcrossed with T. boeoticum in order to substitute the boeoticum genome into urartu cytoplasm. The second backcross progeny from this substitution is only partially male sterile. Literature Cited DHALIWAL, H.S., and B.L. JOHNSON. 1975. Anther morphology and the origin of the tetraploid wheats. Amer. J. Bot. (in press). JOHNSON, B.L, 1975. Identification of the apparent B genome donor of wheat. Can. J. Genet. CytoL 17 : 21-39. MAAN, S.S. and K.A. LUCKEN. 1970. Interaction of Triticum boeoticum cytoplasm and genomes of T. aestivum and T. durum : Restoration of male fertility and plant vigor. Euphytica 19 : 498-508. MAAN, S.S. and K.A. LUCKEN. 1971. Nucleocytoplasmic interactions involving Aegilops cytoplasm and Triticum genomes. J. Hered. 62 : 149-152. SUEMOTO, M, 1973. The origin of cytoplasm of tetraploid wheats. Proc. 4th Int. Wheat Genet. Symp. Columbia, Missouri, U.S.A. pp. 109-113. (Received December 28, 1975) |