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  1. Vol. 8 No. 6, p. 740-743

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Genetic Instability of Ottawa Wheat (Triticum aestivum L.)1

  1. Max A. Urich and
  2. E. G. Heyne2



Spontaneously occurring off-type plants susceptible to leaf rust race 9 were found at a high rate (2.61 per 1,000 seedlings tested) in the progeny of self-pollinated (bagged) spikes of ‘Ottawa’ wheat. They appeared to originate from three different events in a normal, disomic Ottawa population: (1) mutation of the gene for leaf rust race 9 resistance, (2) breakage and loss of a terminal portion of chromosome 6B, which included the gene for resistance, and (3) nonpairing of the two 6B homologues, which resulted in mono-6B and mono-6B telo-6BS aneuploids. A relatively high rate of 6B aneuploids occurred after one generation of self-pollination (1.58 per 1,000 seedlings) and after two generations of self-pollination (2.97 per 1,000 seedlings).

Spontaneously occurring white-glumed spikes ere found at the rate of 1.8 and 2.4 per 10,000 spikes in foundation and registered Ottawa, respectively. Those off-types had either a ditelo or di-iso constitution, indicating loss of an arm of chromosome lB. They probably originated from nonpairing of an 1B bivalent and subsequent misdivision and recombination of an 1B univalent.

Nonhomology did not appear to cause nonpairing which was not random but affected chromosomes 1B and 6B more frequently than other chromosomes. This study suggests that Ottawa has some type of genetic malfunction that prevents chromosomes 1B and 6B from pairing in all meiotic cells.

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