Relationships between inbreeding, meiotic irregularity, and fertility in alfalfa

Fertility (seed production) in alfalfa (Medicago sativa L.) is severely depressed by inbreeding; however, little is known of the factors directly responsible for this depression. Irregularities in meiotic behavior could be partially responsible for the inbreeding depression in fertility observed. This study considered relationships between fertility, inbreeding, and irregularity in microsporogenesis. Fertility declined markedly with inbreeding in the materials examined (S0–S3). Irregularity in microsporogenesis, as measured by the percent irregular quartets, (i.e., quartets with micronuclei, supernumerary microspores, or irregular cytokinesis) increased significantly with inbreeding. Increases in quartet irregularity were associated with increases in the number of univalents per pollen mother cell observed at metaphase I. Considering all materials studied, the percentage of irregular quartets was negatively and significantly correlated with fertility as both a seed and a pollen parent. In more detailed analyses, it was observed that the percent irregular quartets was negatively associated with fertility as a pollen parent only when levels of irregularity were relatively high. No association was observed between the percent irregular quartets and fertility when levels of irregularity were relatively low.Key words: Medicago, microsporogenesis, seed production, breeding, fertility.

Substitution of rye chromosome 5R for its three wheat homoeologues

SUMMARYChromosome 5R of Secale cereale var. Imperial has been substituted for chromosomes 5A, 5B and 5D of hexaploid wheat. There is evidence of compensation, in terms of vigour, in all substitution lines. Chromosome 5R rectifies the male sterility of nullisomics 5A and 5D; however, it is unable to circumvent the meiotic irregularity and male sterility of 5B-deficient stocks. Another instance of wheat-rye chromosome pairing, in the absence of chromosome 5B, is reported. The data reported here demonstrate that the long arm of 5R is the more essential arm and indicate that chromosome 5R is homoeologously related to the group 5 chromosomes of wheat.