Comparative analysis of the meiotic effects of wheat ph1b and ph2b mutations in wheat x rye hybrids

Wheat-wheat and wheat-rye homoeologous pairing at metaphase I and wheat-rye recombination at anaphase I were examined by genomic in situ hybridization (GISH) in wild-type (Ph1Ph2) and mutant ph1b and ph2b wheat x rye hybrids. The metaphase-I analysis revealed that the relative contribution of wheat-rye chromosome associations in ph2b wheat x rye was similar to that of the wild-type hybrid genotype but differed from the effect of the ph1b mutation. The greater pairing promotion effect of the ph1b mutation appears to be relatively more on distant homoeologous partner metaphase-I associations, whereas the lower promoting effect of ph2b is evenly distributed among all types of homoeologous associations. This finding reveals that distinct mechanisms are involved in the control of wheat homoeologous pairing by the two Ph genes. The frequency of wheat-rye recombination calculated from anaphase-I analysis was lower than expected from the metaphase-I data. A greater discrepancy was found in ph2b than in ph1b wheat x rye hybrids, which may suggest a more distal chiasma localization in the former hybrid genotype.