Meiotic instability of common wheat strains derived from Triticum timopheevi Zhuk. crosses

Summary Meiotic instability was studied in four strains of common wheat derived from crosses involving a Triticum timopheevi derivative, C.I. 13093, and the common wheat varieties Cheyenne and Minturki. A wide range in the percentage of normal cells at six stages of meiosis, MI, AI, dyad, MII, AII, and quartet, was found. The date of sporocyte sampling influenced meiotic irregularities at six stages of meiosis. Florets from the same spikes differed in the percentage of normal cells at all the meiotic stages except MII. Plants within strains differed significantly at the MI and quartet stages only. Except at AI stage, spikes collected on the same day did not differ significantly. Apparently, environment during premeiotic phase determined the extent and the pattern of meiotic instability in spikes of these strains.Chromosome counts were taken on 213 of the highly aberrant PMC at MI. Among these, 44 different chromosome numbers ranging from 4 to 76 per cell were recorded. Cells with deviating numbers from 22 to 28 were the most frequent (30.52 percent). Chromosome numbers 12, 17, 21, 22, 24, 26 and 28 occurred in 43.9 percent of the aberrant PMC, and the number of cells with these chromosome numbers ranged from 9 to 15.The metaphase 1 chromosome pairing in deviating PMC was not related to the number of chromosomes in these PMC. Apparently, deviating PMC had a random assortment of chromosomes. In aberrant PMC and others with apparently normal chromosome numbers (but irregular meiosis) homeologous chromosomes may pair. Functional gametes from such cells may perpetuate meiotic instability that had persisted in these three advanced generation common wheat strains of hybrid origin.