Genotypic frequencies of phosphoglucose isomerase allozymes in bean rust (Uromyces appendiculatus) populations estimated by densitometry

Phosphoglucose isomerase (PGI) is a dimeric enzyme in germinating urediniospores of Uromyces appendiculatus. Three distinct bands occur in heterozygous isolates after starch gel electrophoresis. Transmission densitometry was used to estimate the frequency of the homozygous slow (S), homozygous fast (F), and heterozygous (H) individuals in mixed preparations of urediniospores. Areas under each band peak were transformed to genotypic frequencies by comparison with standard 1:1 (F:S)and 100% H preparations. Estimated genotypic and allelic frequencies in prepared mixtures were linearly related to the actual frequencies. Correspondence of estimated with actual frequencies was high, generally differing by 10% or less. Three of 10 field collections examined were polymorphic for PGI allozymes, and two of these were apparently in Hardy-Weinberg equilibrium.