| Reduced Male Fertility and Reduced Plant Vigor T. aestivum and/or T. durum plants with the cytoplasm of Ae. bicornis, Ae. umbellulata, or Ae. cylindrica had complete or partial male sterility and reduced plant vigor (Table 1). In general, the T. durum genome was more sensitive to the alien cytoplasm than the T. aestivum genome. Fewer backcrosses were necessary to eliminate nuclear genes or chromosomes from the cytoplasm-donor species in the substitution-backcross series of T. durum than in the substitution-backcross series of T. aestivum. Therefore, the reduction in vigor of T. durum plants with alien cytoplasms was usually observed in early backcross progenies, and the reduction in vigor of T. aestivum plants with the alien cytoplasms became apparent only in advanced backcross progenies. The reduction in plant vigor was influenced by environmental factors. In the greenhouse, T. durum and T. aestivum in some alien cytoplasms had noticeably poorer growth during the fall growing season than during the spring season. Apparently the photoperiod and the light intensity during the growing season influenced plant vigor. However, under field conditions photoperiod and light intensity were not limiting factors, and reduced vigor under field conditions may have been due to cool nights and low soil temperatures during the spring season. T. durum and T. aestivum plants with T. boeoticum cytoplasm (MAAN and LUCKEN 1967, 1970) had stable male sterility under all environments tested. T. durum and T. aestivum plants with Ae. umbellulata (MAAN 1972) or S. cereale (MAAN and LUCKEN 1971b) cytoplasm had complete male sterility during the fall and partial fertility during the spring season in the greenhouse. The plants with Ae. umbellulata cytoplasm had normal anther extrusion and normal-appearing anthers; however, they did not dehisce, and seed set on bagged heads was poor. The manual bursting of anthers with forceps and hand pollination increased seed set on these comon-wheat plants. Similarly, T. aestivum plants with S. cereale cytoplasm set a few selfed seeds during the spring season, but anther extrusion was less noticeable in plants with S. cereale cytoplasm than in plants with Ae. umbellulata cytoplasm. T. durum and T. aestivum plants with Ae. bicornis cytoplasm (from amphidiploid Ae. bicornis- T. boeoticum) were reported to have normal fertility and plant vigor (MAAN and LUCKEN 1972). Now after 14 back-crosses, T. durum plants with Ae. biocrnis cytoplasm have complete male sterility and reduced plant vigor during the fall and partial fertility and near-normal vigor during the spring season in the greenhouse. T. aestivum plants with Ae. bicornis cytoplasm (after 10 backcrosses) have relatively less reduction in plant vigor and fertility than T. durum plants with Ae. bicornis cytoplasm. Also. T. aestivum with Ae. variabilis cytoplasm was reported to have normal fertility and plant vigor (MAAN and LUCKEN 1972). However, in subsequent backcross progenies a progressive reduction in plant vigor became apparent. T. durum and T. aestivum plants with the cytoplasms of Ae. cylindrica, Ae. longissima, Ae. sharonensis, and Ae. heldreichii had male sterility (Table 1), and T. durum plants with these cytoplasms also had reduced vigor. Additional backcrosses are necessary (in the substitution backcross series with T. aestivum) before valid conclusions can be made about the reduction in plant vigor in common wheat. MAAN and LUCKEN (1971a, 1972) reported that T. durum and T. aestivum with Ae. squarrosa cytoplasm had normal fertility and plant vigor. Additional backcrosses have now been made, and T. aestivum plants with Ae. squarrosa cytoplasm (Ae. squarrosd/12 T. aestivum) still have normal fertility and plant vigor. However, results from additional backcrosses with the T. durum recurrent parent indicated that complete substitution of the T. durum genome into Ae. squarrosa cytoplasm resulted in non-germinating seeds. All seedlings from the fourth and fifth backcrosses with T. durum pollen had 29 chromosomes (2n=14II+a complete or telocentric D-genome chromosome). The sixth backcross with T. durum pollen again resulted in plants with the maternal chromosome number (2n+29; 14II+1I or tI). However, seedlings were obtained by transferring the embroys from the mature non-germinating seeds to an artificial medium for embryo culture as described by SCHOOLER (1960). Apparently a growth factor in the embryo culture medium or an addition of a D-genome chromosome to the T. durum genome improved interactions between the T. durum genome and the Ae. squarrosa cytoplasum. |
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