THE SCS AND VI GENES CORRECT A SYNDROME OF CYTOPLASMIC EFFECTS IN ALLOPLASMIC DURUM-WHEAT

The nucleus of Triticum turgidum L. var. durum is incompatible with cytoplasms of Aegilops squarrosa L., Ae. cylindrica Host, Ae. uniaristata Vis., and Ae. longissima S. & M. However, durum lines with these cytoplasms were obtained by adding a telosome from Ae. uniaristata (un telosome) or a 1 DL telosome from T. aestivum L. 'Selkirk'. The Ae. squarrosa and Ae. cylindrica 29-chromosome plants with IDL telosome were partially fertile. While Ae. uniaristata or Ae. longissima 29-chromosome plants with IDL or un telosome were male sterile. The four alloplasmic lines set a few plump and a large number of shrivelled seed from crosses with euploid durum. Only plump seed germinated and produced 29-chromosome plants in successive backcrosses. The telosomes must have a species cytoplasm specific (scs) gene(s) that improved nucleocytoplasmic (NCC) and embryo-endosperm compatibility (EEC), but scs was not transferred to a durum chromosome because telosomes remained meiotically unpaired in 29-chromosome plants. However, a scs gene with similar effects was transferred from T. timopheevii Zhuk. to Ae. longissima euploid durum. The resulting plants were male sterile and set a 1:1 ratio of plump and shrivelled seed. This paper reports that a vitality gene (Vi) restored NCC, EEC, seed viability, fertility, and vigor to Ae. longissima euploid F1's with scs from T. timopheevii. F1 progeny had a 1:1 ratio of fertile plants of normal vigor and low vigor plants (LVP). Thus, Vi had xenia effect, improved EEC, and corrected a syndrome of cytoplasmic effects in 50% of the F1's where Vi was epistatic or dominant to scs. The F2 and sucessive selfed progeny segregated for LVP but true breeding fertile plants were not obtained. Either scs and Vi were alleles, heterosexual gametes with scs and Vi were incompatible, scs had preferential transmission through the heterosexual gametophytes, or Vi was inactivated or remained unexpressed. Thus, scs and Vi had an unorthodox manner of inheritance and expression.