GENETIC ANALYSES OF MALE-FERTILITY RESTORATION IN WHEAT .4. FERTILE LINE WITHOUT MAJOR RF GENES

Substitution of the common wheat (Triticum aestivum L.) nucleus into T. timopheevii Zhuk. cytoplasm results in cytoplasmic male-sterility. Two partially dominant Rf1 and Rf4 genes on chromosomes 1A and 6B, respectively, restore fertility. But lines with individual Rf1Rf1 or Rf4Rf4 genes are known to have unidentified recessive gene(s) that complement fertility restoration. In this study, expression of recessive genes was examined in the absence of major Rf genes. The procedure involved crossing male-sterile 'Chris' monosomic 1A (cms-Chris mono-1A) to a Rf1Rf1 rf4rf4 line, backcrossing cytologically identified F1 mono-1A to euploid Chris (rf1rf1 rf4rf4), selfing fertile backcross F1 mono-1A, and selecting fertile disomics in the selfed progeny. Thus, Rf1 was replaced by rf1 of Chris. Similarly, rf4 replaced Rf4 in monosomics of a second cross: cms-Chris mono-6B/rf1rf1 Rf4Rf4 line, F1 mono-6B//Chris. In the latter backcross progeny, monosomics were male steriles, but some mono-1A were fertile in the former backcross progeny. In their selfed progeny fertile disomics were selected. Thus, a true-breeding fertile line with T. timopheevii cytoplasm, but without the major Rf genes was obtained.