DISTORTED INHERITANCE OF STEM-RUST RESISTANCE OF TIMSTEIN WHEAT CAUSED BY A POLLEN-KILLING GENE

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Abstract
The approximate 9:7 ratio obtained for resistance to stem rust in the wheat cross Chinese Spring (susceptible) x Timstein (resistant) was found to be due to a single gene conditioning resistance (Srll) and a linked gene (ki) affecting pollen. Ki (pollen killer), present in Chinese Spring, causes the abortion of microspores carrying ki in Kiki plants. It is linked to srll with about 9% crossing over. This reduces male transmission of Srll to 9% and thereby changes the expected 3:1 ratio to about 9:7 in F2. Evidence was obtained that Kiki microspores abort in KiKiki trisomics but not in Kikiki. Apparently even ki pollen survives in Kikiki. In KiKikiki tetrasomics the high rates of abortion indicates that most or all Kiki pollen is killed. It appears that killing is an effect of maternal tissue on microspores and that its severity depends on the relative dosage of Ki and ki. Certain varieties tested showed virtually no pollen abortion in their hybrids with either Chinese Spring (KiKi) or Thatcher-6B (kiki). This suggests that there may be other alleles at the Ki locus.