| A triticale breeding strategy drawn from genetic analysis
of nucleo-cytoplasmic interaction Y. Yasumuro, N. Nakata and M. Sasaki Faculty of Agriculture, Tottori University, Tottori 680, Japan The wheat cytoplasm is euplasmic for wheat chromosomes but alloplasmic for rye chromosomes of triticale (TC), the converse being the case in TC with rye cytoplasm (Sasaki et al 1983). Thus both the wheat and rye cytoplasms suppress the expression of nuclear genes of TC in the way of various kinds of interaction. We have accumulated different cases of the genetic interactions between nuclear genes and cytoplasms using eu- and alloplasmic lines of Chinese Spring (CS) ditelosomics, rye and TC. Those interactions can be classified as shown in Table 1. Examples of the Genetic Interaction Types I. NN-type interaction' (1) Hybrid chlorosis between wheat and rye was controlled by complementary genes. Hch1 and/or Hch2, on the 1BS and 1DS of CS, and Hch3 on the 6R of inbred rye line IR14 (Sasaki and Yasumuro 1974, Nakata et al 1989). (2) Nucleolar organizer activity of the 6B of wheat was epistatic effect over the 1R of rye even in rye nuclei (Nakata et al 1986b). II. NC-type interaction (1) Ni x Ci: This type of interaction showed a strong affinity between nuclear and cytoplasmic genes of the same species. (i) Midget chromosome originated from rye chromosome 1R was found in the CS nucleus with rye cytoplasm. The midget chromosome was necessary for the endosperm development of the wheat line with rye cytoplasm, i.e., a strong interaction was found between the gene on the 1R and rye cytoplasmic genome (Nakata et al 1986c). (ii) The CS line with Agropyron intermedium cytoplasm had a chromosome of intermedium origin which had a recovering effect of the plant vigour (Tokiwa et al 1986). (iii) Chromosome 2D in TC lines with aestivum cytoplasm and chromosome 2R in TC lines with cereale cytoplasm were responsible for the high seed fertility(Yasumuro et al 1987). (2) Ni x Cj : This type of interaction showed deleterious effect contrary to Ni x Ci. (i) The chiasma frequency of a inbred rye line with aestivum cytoplasm ((aes)-IR115) was lower than that of the line with rye cytoplasm ((cer)-IR115), though the cytoplasmic differences were not found in chiasma frequency in the other IR lines (Nakata et al 1986a). III. CNN-type interaction (1) Hybrid weakness between wheat and rye was caused by complementary gene action and this effect was inhibited by speltoides cytoplasm. Complementary genes De1 on the 7BL of CS and De2 of the inbred rye line, IR 129 (chromosome not identified) caused weak plant growth in the wheat-rye hybrid lines with wheat, rye or some Aegilops cytoplasms (NN-type interaction) however, the line with speltoides cytoplasm showed normal plant growth, that is, this cytoplasm had the inhibitor (Ide) to the nuclear genotype De1-De2-, recovering normal plant vigour (Yasumuro et al 1983 ; Sasaki et al 1986). (2) Abnormal pollen tetrad formation was found at high frequency in the TC lines with timopheevi cytoplasm in the cross-combinations of CS with IR46 or IR129 (Yasumuro et al 1985). IV. NCN-type interaction (1) Wheat endosperm glutenin genes on the 1BL and 1DS of CS were suppressed by a complementary effect between the 1AS of CS and cytoplasmic genomes of aestivum or ovata (Yasumuro et al 1985). |
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