Interacting Nucleo-Cytoplasmic Systems

Common wheat with the cytoplasm of T. boeoticum, Ae. umbellulata, or S. cereale had reduced fertility and plant vigor. R5 and R6 restored male fertility and plant vigor to wheat with T. boeoticum cytoplasm (MAAN and LUCKEN 1970). R5 and R6 restored partial fertility and plant vigor to wheat with the cytoplasm of Ae. umbellulata or cereale. R4 (a common wheat with male-fertility-restoring genes from amphidiploid T. timopheevi- Ae. squarrosa) restored fertility and plant vigor to wheat with S. cereale cytoplasm. But R4 did not restore fertility or plant vigor to wheat with T. boeoticum cytoplasm. Also, one S. cereale chromosome added to the wheat genome restored fertility to common wheat with rye cytoplasm. This rye chromosome did not restore fertility to common wheat with the cytoplasm of Ae. umbellulata or T. boeoticum. These nucleo-cytoplasmic interactions clearly indicate cytoplasmic differences among T. boeoticum, Ae. umbellulata, and S. cereale (Table 1).

Similarly, differential fertility-sterility interactions of the F₁ hybrids from crosses with R5 and R6 indicated that T. timopheevi and T. Zhukovskyi differed cytoplasmically from T. araraticum, T. dicoccoides var. nudiglumis, and Ae. speltoides. T. timopheevi with the cytoplasm of Ae. speltoides had complete male sterility and reduced plant vigor. But T. timopheevi with the cytoplasm of T. araraticum or T. dicoccoides var. nudiglumis had normal fertility and plant vigor, indicating that there are cytoplasmic differences between Ae. speltoides and T. araraticum or T. dicoccoides var. nudiglumis (MAAN and LUCKEN 1972).

The review of literature and the results presented in this paper show that in the Triticinae cytoplasmic differences among species can be detected by the substitution of the genome of one species into the cytoplasms of other related species. The cytoplasms of the newly established nucleo-cytoplasmic combinations may show differential effects on the expression of the substituted genome. The cytoplasmic effects become apparent due to the absence of certain nuclear genes in the substituted genome. Certain cytoplasms with similar effects on the expression of the substituted genome may differ in their interactions with certain nuclear genes from other related cytoplasm-donor species.

T. durum or T. aestivum genomes have now been substituted into cytoplasms of the following species: T. monococcum, T. boeoticum, T. timopheevi, T. Zhukovskyi, T. araraticum, T.dicoccoides var. nudiglumis, Ae. speltoides, Ae. squarrosa, Ae. bicornis, Ae. longissima, Ae. sharonensis, Ae. umbellulata, Ae. caudata, Ae. heldreichii, Ae. variabilis, Ae. ovata, Ae. cylindrica, and S. cereale. Among these species, 16 distinct cytoplasms have been demonstrated. Apparently, Triticum species with genomes AABB or AABBDD have the same or similar cytoplasms. The cytoplasms of the species including Ae. uniaristata, Ae. biuncialis, Ae. triuncialis, Ae. triaristata, Ae comosa, Ae. kotschyi, Agropyron elongatum, and Haynaldia villosa are currently under study. Apparently, cytoplasmic differences among species of Triticinae are common, and cultivated wheats with different cytoplasms are being developed to study possible economic use of cytoplasmic variability in wheat improvement.

(Received August 10, 1973)