GENETIC VARIABILITY INAEGILOPS SPELTOIDESAFFECTING HOMOEOLOGOUS PAIRING IN WHEAT

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Abstract
Three Chinese Spring ditelocentric lines and four Agropyron telocentric addition lines were crossed with a single population of Aegilops speltoides. Chromosome pairing was studied in the hybrid plants. The mean chiasma frequencies per cell in different hybrid plants indicate the existence of three different genotypes in the population of Ae. speltoides each differing significantly in ability to suppress the diploidizing mechanism in polyploid wheat. Plants at the three levels of pairing showed means of 6.4, 10.4 and 15.0 chiasmata per cell, respectively.Agropyron telocentric chromosomes did not pair with their wheat homoeolgues at the lowest pairing level. At intermediate and high pairing levels they did pair with wheat chromosomes. The increase in pairing of Agropyron telocentrics paralleled the increase in chiasma frequency per cell.The action of genes controlling homoeologous synapsis is discussed and it is suggested that pairing affinity between chromosomes may result from the interaction between two factors: homology in nucleotide sequences at specific sites in chromosomes, and degree of activation of these sequences.