I. Research Notes

Cytoplasmic variability in Triticinae¹⁾

S. S. MAAN

Department of Agronomy, North Dakota State University, Fargo, N. D. 58102, U.S.A.

In higher plants cytoplasmic inheritance is essentially maternal and cytoplasmic genes are seldom transmitted through the male gametes. Therefor, phenotypic differences in F₁ hybrids from reciprocal crosses (JONES 1912), and differential segregation in F₂ or backcross progenies from reciprocal crosses generally indicate cytoplasmic differences between the parents (BATESON and GAIRDNER 1921, CHITTENDEN 1927, CHITTENDEN and PELLEW 1927, GAIRDNER 1929). The study of allelism or linkage relationships cannot be done among the non-nuclear genes from different cytoplasmic sources in higher plants, because these genes predominantly show maternal inheritance. Therefore, research on cytoplasmic inheritance is limited to the study of cytoplasmic differences and inheritance of nuclear genes controlling cytoplasmic effects. The relative similarities and differences between the hereditary constituents of cytoplasms from different sources are inferred from their interactions with certain nuclear genes or genotypes (MICHAELIS 1954, KIHARA 1951, FUKASAWA 1959).

In the Triticinae, F₁ hybrids from reciprocal crosses involving the species of Triticum have not been reported to differ phenotypically, even when the parental species had different cytoplasms. Hybrids between these species are usually completely male sterile and have a high degree of female sterility. Therefore, differential segregation in the F₂ cannot be studied. Complete elimination of the nuclear genes or chromosomes of the cytoplasm-donor species by extensive backcrossing with the recurrent male parent is usually necessary to reveal cytoplasmic effects on the expression of the substituted genome, because of the aneuploidy and associated sterility in the early generations.

Therefore, cytoplasmic differences among the species of Triticum and Aegilops have been studied by the reciprocal-nuclear-substitution method (KIHARA 1951, FUKASAWA 1953). KIHARA and FUKASAWA selected Triticum and Aegilops species with no pairing homology between their chromosomes during meiosis in F₁ hybrids to prevent crossing over between the alien genomes. They reintroduced the Aegilops genome into Aegilops cytoplasm by backcrossing, to prove that Aegilops cytoplasm remained unaltered in malesterile wheats Aegilops cytoplasm. The cytoplasms of Ae. caudata and Ae. ovata affected the expression of the substituted wheat genome differently. The T. aestivum plants with Ae. caudata cytoplasm had male sterility and pistillody (KIHARA 1951), and T. durum plants with Ae. ovata cytoplasm had male sterility and delayed maturity (FUKASAWA 1953). WILSON and Ross (1962) reported that T. aestivum with T. timopheevi cytoplasm had male sterility.